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HERBOLOGIA

An International Journal on Weed Research and Control

Vol. 7, No. 1, April 2006

Issued by: The Academy of Sciences and Arts of Bosnia and Herzegovina and The Weed Science Society of Bosnia and Herzegovina

Editorial Board Paolo Barberi (Italy) Shamsher S. Narwal (India) Vladimir Borona (Ukraine) Zvonimir Ostojić (Croatia) Daniela Chodova (Czech Republic) Danijela Petrović (B&H) Mirha ðikić (B&H) Marko Skoko (B&H) Aniko Farkas (Hungary) Lidija Stefanović (S&M) Azra Hadžić (B&H) Taib Šarić (B&H) Senka Milanova (Bulgaria) Dubravka Šoljan B&H) Ševal Muminović (BiH)

Editor-in-Chief: Prof. Dr. Taib Šarić Technical Editor: Dr. Mirha ðikić

Address of the Editorial Board and Administration Herbološko društvo BiH (Poljoprivredni fakultet) Sarajevo, Zmaja od Bosne 8, Bosna i Hercegovina Phone: ++387 33 653 033, Fax: ++387 33 667 429

E-mail: [email protected]

Published four times a year The price of a copy of the Journal: 15 €

Printed by

Štamparija GARMOND GRAPHIC, Sarajevo

CONTENTS

Page

1. A Jubilee……………………………………………………………...1 2. V. D. Mircov, I. ðalović, Z. Brocić: Results of weed control in

field potatoes…………………………………………………………3

3. Anikó Farkas: Soil management and tillage possibilities in weed control………………………………………………………………..9

4. B. Konstantinović, Maja Meseldžija, Dragana Šunjka: Resistance study of Amaranthus retroflexus L. species population to the herbicide imazethapyr……………………………………………….31

5. Tsvetanka Dimitrova, Senka Milanova: Influence of the adjuvant

Desh on the efficacy and selectivity of imazamox 40 a.i.l-1 (Pulsar 40)

in three perennial legume crops……………………………………..41 6. Z. Pacanoski: Herbicide-resistant crops - advantages and risks…...47 7. T. Šarić, I. ðalović: Production of allergenic pollen by ragweed (Ambrosia artemisiifolia L.) is increased in CO2-enriched atmospheres…………………………………………………………59 8. G. Malidža, V. Janjić, I. ðalović: Genetically modified herbicide–tolerant crops – state and perspectives............................67 Instruction to Authors in Herbologia………………………………….94

Herbologia Vol. 7, No.1, 2006.

A Jubilee

50 years of Prof. Taib Saric’s work in science and higher education

Professor Taib Saric, Editor of Herbologia, this spring celebrates 50 years of his fruitful and devoted work in agricultural science and university education. His contribution to agricultural profession, science and education has been immense. Although retired, as professor emeritus he continues to give his significant contribution, particularly in guiding M.S. and Ph.D. candidates, and in editting the International Journal for Weed Research and Control Herbologia.

By this modest article we wish to thank our respectable and prominent Professor for the tremendous work he has done during five decades and to wish him good health, to stay further with us for many years on the benefit of agricultural science and practice.

Short curriculum vitae

Profesor Taib Saric was born in Capljina (Bosnia and Herzegovina) in 1934. He took his B.S., M.S. and Ph.D. degrees in agronomy from the University of Sarajevo. He studied weed science and agroecology at post-master′s study at Kansas State University, Manhattan, Ks. and Bucknell University in Pennsylvania, U.S.A., and post-doctoral study in weed science at the Wageningen Agricultural University in the Netherlands. He joined the Indian Agricultural Research Institute in New Delhi for two years performing research on subtropical field crops.

From 1962 he has been working with the Faculty of Agriculture of the University of Sarajevo as an assistant, assistant professor, associate professor, full professor and professor emeritus in agroecology, soil management, weed science, and environmental protection, participating in education of 44 generations of students.

In the last 30 years he was Editor-in-Chief of three scientific journals, the last of them being Herbologia. He published more than 100 research papers, about 600 professional articles, and 24 books (with updated editions a total of 44 books) on soil management, agroecology, weed science, and environmental protection. His book Soil Management (four editions) was the major textbook for students of agronomy in Yugoslavia. His Weed Atlas (five editions), with nomenclature in nine languages, has been used in about 30 countries all over the world.

He was one of the founders of the Weed Science Society of Yugoslavia (in Sarajevo, 1973) and was its president. He was one of the founders of the European Weed Research Society (EWRS, in Paris, 1975) and a member of its Scientific Committee and Educational Committee. During 30 years he was National Representative of Yugoslavia, and latter on of Bosnia and Herzegovina, to the EWRS. He led the foundation of the Weed Science Society of Bosnia and Herzegovina.

A Jubilee

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In 1977 at the Faculty of Agriculture in Sarajevo he founded the first postgraduate study in weed science with teachers from Yugoslavia, Switzerland, Italy, etc.

He presented numerous papers with results of his research at Symposia and Congresses held in Uppsala, Moscow, Warshaw, Leipzig, Brno, Bratislava, Keszhtely (Hungary), Poznan, Brighton, Gent, Sydney, etc. He was chairperson at the EWRS Symposia in Uppsala, Paris and Lisbon. As a guest of the Indian Government he delivered the invited introductory lecture on the methods of promotion of field crop production on the 63rd Indian Science Congress, Section for Agriculture, in Vishakhapatnam in 1976. After that, he lectured at graduate studies at Agricultural Universities in New Delhi, Hyderabad and Bangalore.

He was a foreign peer-reviewer of several Ph.D. thesis at foreign universities and in electing full professors at them.

For his rich scientific opus and prolific profesional publications Prof. Saric was conferred the State Award „Veselin Maslesa“. He was twice nominated a laureate of the World Food Prize (known informally as the Nobel Prize for Food and Agriculture). He is a member of the Academy of Sciences and Arts of Bosnia and Herzegovina.

Contribution to weed science

In the course of 50 years, Professor Saric greatly contributed to weed science through his research, his numerous publications (papers and books) and through educating many generations of undergraduate, postgraduate and doctoral students. His research was particularly devoted to spreading of new, invasive weed species, various ways of weed control, herbicide testing and application, and crop-weed allelopathy. In studying the weed flora of Bosnia and Herzegovina he continued the research started by Komsa and Vaskovic in the first decades of the 20th century. He pioneered the introduction of herbicides in Bosnia. He was one of the pioneers of weed science in Yugoslavia. He took part in founding and work of the EWRS. He was among the organizers of the most of national and international Weed Symposia and Congresses held in Yugoslavia.

His great knowledge and very rich experience Prof. Saric has all the time readily transfered to us, his students and coworkers, to other agronomists, and to farmers. He will for long time remain an unparalleled coryphaeus of our weed science, as well as the science of soil management and agroecology.

Prof. S. Muminovic

Herbologia Vol. 7, No.1, 2006.

RESULTS OF WEED CONTROL IN FIELD POTATOES

Vlad Dragoslav Mircov1, Ivica ðalović2, Zoran Brocić3

1University of Agricultural Sciences and

Veterinary Medicine of Banat – Timisoara, Romania 2Faculty of Agronomy – Cacak, Serbia and Montenegro

3Faculty of Agriculturae, Belgrade – Zemun, Serbia and Montenegro

Abstract

Weed competition can reduce yield and potato quality, affecting tuber size, weight, and quantity. In this research paper it was compared the efficacy of 10 herbicide treatments for controlling prostrate pigweed, kochia, and Russian thistle in a low organic coarse–textured soil and to determine their effect on marketable potato yields.

Study results emphasize the need for good weed control for optimum potato yields. Metribuzin applied alone or in combination with metolachlor, pendimethalin, or trifluralin plus EPTC gave excellent broadleaf weed control and the highest marketable potato yields. Key words: weeds, weed control, field potatoes.

Introduction

Weed competition can reduce yield (VanGessel and Renner, 1990) and potato quality (VanGessel and Renner, 1990), affecting tuber size, weight, and quantity (Nelson and Thoreson, 1981; Wall and Friesen, 1990a, Rosales–Robles et. al., 1999). Weeds interfere with harvest, causing more potatoes to be left in the field and increasing mechanical injury (VanGessel and Renner, 1990). If a mixed population of annual weeds is allowed to compete with potatoes all season, each 10% increase in dry weed biomass causes a 12% decrease in tuber yield. One redroot pigweed (Amaranthus retroflexus L.) or barnyardgrass [Echinochloa crus–galli (L.) Beauv.] per meter of row reduced marketable tuber yield 19 to 33% (VanGessel and Renner, 1990; Baziramakenga and Leroux, 1998).

The critical period for weed removal in potatoes is about 4 to 6 weeks after planting. Weeds emerging 4 weeks after planting are suppressed by crop growth (Thakral et. al., 1989). These weeds may not reduce tuber yield through competition, but can interfere with harvest operations.

Mechanical cultivation does not remove weeds within the row and may damage potato plants and reduce yields (Nelson and Giles, 1989). Herbicides can reduce the number of cultivations required and enhance weed control particularly during the early season before hilling. Many herbicides are

V.D. Mircov et al.

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approved for use on potatoes grown on medium– and fine–textured, high–organic soils. Relatively little information is available regarding the effectiveness and safety of herbicides for potatoes grown in low–organic matter, coarse–textured soils.

The objectives of this research were to compare the efficacy of 10 herbicide treatments for controlling prostrate pigweed, kochia, and Russian thistle in a low organic, coarse–textured soil and to determine their effect on marketable potato yields.

Materials and methods

Field trials were conducted over a three–year period from 2002 to 2004 at the experimental station University of Agricultural Sciences and Veterinary Medicine of Banat – Timisoara in Romania. The soil was a chernozem. Soils were fertilized according to Timisoara recommendations based on soil tests (N=0.219 mg/100 g soil, P2O5=21.4 mg/100 g and K2O=31.6 mg/100g soil). Fields were plowed, disked, leveled, and hilled prior to planting.

A randomized complete block design with three replications was used. The distance between rows was 75 cm and the distance between the plants in a row was 33 cm, density being 40.000 plants per hectare. The seed of class A was used. Potato sowing on April 14, 2002 (cv. Desiree); April 20, 2003 (cv. Adora); and April 19, 2004 (cv. Adora).

Prostrate pigweed, kochia, and Russian thistle were broadcast seeded at a rate of 1.0 kg/ha–1 each and harrow incorporated prior to planting. The chemical designations for the proprietary herbicides evaluated were:

Common name Trade name metolachlor Dual EPTC Eptam fluorochloridone Racer (proposed) metribuzin Sencor pendimethalin Prowl trifluralin Treflan

Preplant incorporated (PPI) treatments were applied April 14, 2002;

April 16, 2003; and April 19, 2004 and immediately incorporated to a depth of 4 to 5 cm with a tractor–driven rotary tiller. Preemergence (PRE) treatments were applied April 30, 2002; April 24, 2003; and April 22, 2004 and immediately incorporated with 1–2 cm of sprinkler–applied water.

Visual evaluations of crop injury and weed control were made July 17, 2002; July 21, 2003; and June 23, 2004. Weed control was based on a 0–to–

Results of weed control in field potatoes

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100% scale, where 0 = no control and 100 = no living weeds. Infestations were light throughout the experimental area for all three weeds. Weeds were hoed from the weed–free controls as needed, beginning one month after planting and continuing through August.

Potatoes were mechanically harvested with a tractor–driven potato digger on October 2, 2002; September 22, 2003; and September 19, 2004 from 1,5 m of the center two rows of each plot. The harvested potatoes were graded to separate marketable tubers.

Tubers that were diseased, less than 28/55 mm were discarded. Previous research indicates that specific gravity is independent of weed density, so specific gravity was not measured. Values for weed control and marketable yield were subjected to analysis of variance, and treatment means were separated by Fisher’s LSD test at the 5% significance level. There was no significant year–by–treatment interaction, so data were combined for all three years.

Results and discussion

Fluorochloridone was the only treatment that injured potato plants during all three years (data not shown). At both rates, potato plants exhibited chlorosis along leaf veins, and plants were slightly reduced in size. As the season progressed, injury symptoms diminished, and there appeared to be no difference in foliar growth among all treatments at harvest.

All herbicide treatments controlled 100% of prostrate pigweed (table 1). Trifluralin, in combination with metolachlor or with EPTC, controlled less than 95% of kochia (an average of 89% and 88%, respectively). Adding metribuzin to trifluralin plus EPTC increased control to 100%. Pendimethalin alone or in combination with EPTC controlled less than 75% of Russian thistle.

Adding metribuzin to pendimethalin increased Russian thistle control to 95%. All other treatments controlled 90% or more of Russian thistle. The unweeded control yielded the least marketable potatoes of all treatments (table 1) and produced 61% less than the weed–free control. The greatest potato tuber yields were noted in plots treated with metribuzin alone or in combination with metolachlor or pendimethalin. Pendimethalin alone and in combination with EPTC failed to control Russian thistle, and marketable potato yields were lowest among treated plots. Adding metribuzin to pendimethalin increased Russian thistle control to 95%, and increased marketable tuber yields by 54% over pendimethalin alone. Previous research has indicated that pendimethalin may have a beneficial effect on potato yields beyond that of weed control, possibly by inducing deeper rooting (Nelson and Giles, 1989).

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Table 1. Prostrate pigweed, kochia, and Russian thistle control, and potato yields, averaged over three years (2002–2004).

Weed controla Treatments Timing Rate AMABL KCHSC SASKR

Marketableb potato yield

l/ha–1 % t/ha–1 Trifluralin+metolachlor PPI 0.75+1.5 100 89 95 40.6 Trifluralin+EPTC PPI 0.75+3.0 100 88 95 40.9 Trifluralin+EPTC+metribuzin PPI 0.75+3.0+0.25 100 100 100 42.5 Fluorochloridone PRE 0.25 100 100 90 42.0 Fluorochloridone PRE 0.50 100 100 99 38.5 Pendimethalin PRE 1.0 100 99 69 28.9 Pendimethalin+EPTC PRE 1.0+3.0 100 100 70 33.8 Pendimethalin+metribuzin PRE 1.0+0.25 100 100 95 44.5 Metolachlor+ metribuzin PRE 2.0+0.25 100 100 96 43.3 Metribuzin PRE 0.5 100 100 100 45.4 Weed – free control 100 100 100 43.2 Unweeded control 0 0 0 28.7 Lsd (0.05) 1 5 6 30

aAMABL–prostrate pigweed; KCHSC–kochia; SASKR–Russian thistle; bTubers 28/55 in diameter;

Combining pendimethalin and metribuzin did not significantly change marketable tuber yield as compared with metribuzin alone or the weed–free control in these experiments. Though fluorochloridone at 0.5 l/ha controlled all weeds in this study, marketable tuber yields from this treatment were lower than the weed–free control. The early injury appeared to have a deleterious effect on the crop, at least at the higher rate.

Controlling prostrate pigweed, kochia, and Russian thistle at the beginning of the season increased marketable potato yields more than 100% compared with the unweeded control. Yields were greatest where weeds were controlled with no injury to the crop. All herbicide treatments in this research with the best broadleaf weed control and no crop injury contained metribuzin.

Conclusions

Study results emphasize the need for good weed control for optimum potato yields. Metribuzin applied alone or in combination with metolachlor, pendimethalin, or trifluralin plus EPTC gave excellent broadleaf weed control and the highest marketable potato yields.

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References

NELSON, D. C. AND J. F. GILES. (1989): Weed management in two potato (Solanum

tuberosum) cultivars using tillage and pendimethalin. Weed Sci. 37:228–232. NELSON, D. C. AND M. C. THORESON. (1981): Competition between potatoes (Solanum

tuberosum) and weeds. Weed Sci. 29:672–677. THAKRAL, K. K., M. L. PANDITA, S. C. KHURANA, AND G. KALLOO (1989): Effect

of time of weed removal on growth and yield of potato. Weed Res. 29:33–38. VANGESSEL, M. J. AND K. A. RENNER (1990): Redroot pigweed (Amaranthus

retroflexus) and barnyardgrass (Echinochloa crus–galli) interference in potatoes (Solanum tuberosum). Weed Sci. 38:338–343.

WALL, D. A. AND G. H. FRIESEN. (1990a): Effect of duration of green foxtail (Setaria viridis) competition on potato (Solanum tuberosum) yield. Weed Technol. 4:539–542.

ROSALES – ROBLES, E., J. M. CHANDLER, S. A., SENSEMAN, AND E. P. PROSTKO (1999): Influence of growth stage and herbicide on post – emergence johnsongrass (Sorghum halepense L.) control. Weed Tech. 13: 525 – 529.

BAZIRAMAKENGA, R., AND G. D. LEROUX (1998): Economic and interference threshold densities and quackgrass (Elytrigia repens L.) in potato (Solanum tuberosum L.). Weed Sci., 46: 176–180.

Herbologia Vol.7, No. 1, 2006.

SOIL MANAGEMENT AND TILLAGE POSSIBILITIES IN WEED CONTROL

Anikó Farkas

Szada, H-2111, Szabadság u. 58. E-mail: [email protected]

Abstract

On the basis of the research done on interactions between tillage, soil

condition and weediness, conclusions are listed in three main point and 18 sub-points.

a) Importance of favourable soil condition 1. The weather data of the region affirm the growing frequency of dry

years and the tendency of weather extremes. This shows the necessity of tillage systems that increase the water absorbing and water retaining capacity of the soil. Tillage methods that improve and maintain soil condition may gain prominence. The cover of the soil between crops and the introduction of crops that have a beneficial effect on yield may become a necessity.

2. The effect of previous years can be shown by exact soil condition examinations, and on this basis the methods of improvement can be planned and implemented. The danger of plough-sole and disk-sole is present on the soil. The damage can be alleviated by cultural and biological methods.

3. The disk-sole formed after the stubble-clearing of mustard confirmed the importance of consideration of the soil humidity. Tillage was enough to break compaction close to the surface (with the exception of direct drill), which means that smaller damages can be alleviated.

4. The sowing and germination of oil radish may be influenced by the soil condition changed by the tillage method under the main crop. The soil loosening effect of the oil radish did not appear in case of direct drilling, which probably shows the sensitivity of the crop to the soil condition.

b) Evaluation of soil condition and nutrition level

1. The role of good soil condition and nutrition level in the reduction of drought damage was proven again in wheat, maize, and spring barley.

2. The 35-45 cm deep loosened soil condition had the best influence on yield in the biologically favourable crop rotation system, which was achieved by loosening combined with disking. In dry vegetation period

Aniko Farkas

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the beneficial effect of tillage methods saving the soil structure (cultivator) is also obvious.

3. In winter wheat and maize the yield limiting effect of direct drill is explained by weediness and the hindrance of water movement in the soil of the experimental field, susceptible to sedimentation.

4. The yield of maize sown after oil radish was influenced by the loosening of soil and the nutrition level. While in winter wheat water retaining played a significant role in the whole growing season, in the year of maize there were droughts only in the spring. This shows that the yield of maize was influenced more by the water retaining effect of the soil condition influenced by tillage methods than the precipitation in the growing season.

5. The undisturbed soil condition characteristic of direct drill did not hinder the utilisation of fertilizer in maize, in a year with average precipitation. It can be stated that in case of good nutrition level the yield-reducing effect of compacted or sedimented soil can be alleviated.

c)Evaluation of crop rotation order according to weediness

1. The introduction of mustard in the crop rotation is advantageous because of its weed-limiting, soil-covering and soil-improving effect. With mulching at an optimal date the weed-promoting effect of the catch-crop and the unnecessary water loss can be avoided.

2. On the stubble of mustard and winter wheat weeds characteristic of the area appeared. The higher weed coverage in summer – and thus the better timing of plant protection and the reduction of the seed-bank – was aided by the favourable loosening and humidity of the soil.

3. The soil loosening effect of oil radish was proven by penetration values. It can be used as a protecting crop in dry years if soil humidity loss is curbed during the sowing. The crop improved the cultivability of the soil and was proven to be a good green crop because of its good coverage, rooting and its weed limiting effect.

4. The good weed-limiting effect of the soil is proven, in accordance with the literature, which was further increased be the greater water loss of the soil. This makes the re-evaluaton of the role of ploughing necessary.

5. Tillage methods can be ranked according to their weed-promoting or weed-limiting effect. Among the same conditions direct drill has a weed-promoting, while regular soil-turning has a weed-limiting effect. The weed-promoting or limiting effect of tillage methods without soil turning (loosening, cultivator treatment, disking) is different in each crop and at each nutrition level. Loosening is good to curb the life activity of perennial crops.

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6. The high proportion of Echinochloa crus-galli in the total coverage and its prominent rank in the order proves its adaptation to the different soil and nutrition conditions.

7. The disking under spring barley modified the morpho-biological spectrum. The coverage of the perennial Elymus repens increased, utilizing well the higher level of nutrients.

8. According to the coverage of Ambrosia artemisiifolia ploughing was put at first place in the order of tillage methods. The high number of seeds appearing after the turning of the soil showed greater infection.

9. The competitiveness of Ambrosia artemisiifolia shows a tendency. On soils with low nutrient supply it is more competitive than other weeds and crops. It reacted with higher coverage to the low nutrition level. In case of good nutrition level the weed-limiting effect of cultivated crops is higher, but the development of competing, less dangerous weeds is also better, against which plant protection is easier.

Introduction

The analysis of traditional tillage systems has a significant place

among crop production research topics. In the past 20 years several essays were published on the effect of low tillage and no-till systems on cultivation factors, mainly overboard. The actuality of the analyses is justified by the different cost demand, the necessity and difficulty of creating harmony between the inputs and the more exact knowledge of the plant protection effects of certain systems. In different soil tillage systems tillage influences physical condition and weediness just like crop rotation order and other elements of agrotechnique. One of the unfavourable effects of tillage is soil compaction that presents production risk on 1.4 million hectares in Hungary. Tillage originated compaction can be meliorated by mechanical (loosening) and biological (plants having favourable effect on soil condition) methods.

Weediness is related to soil utilization, tillage and the professionality of plant protection. The yield loss due to weeds can reach or exceed the 30% of the total loss. Due to the damage of weeds, the protection against them is inevitable.

As a consequence of structural and financing problems the cultural condition of the soils deteriorated and weeds proliferated, many species are hard to kill. The problem is not new. As a result of the herbicide utilization of the previous years resistant biotypes gained prevalence and the tolerance against chemicals increased.

The realization that herbicides have a negative effect on the environment and food safety influenced the weed control practice positively.

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One sign is the ambition to keep the weed coverage under the harmful limit. The result is the reducing of herbicide use to reasonable levels, that is also eligible according to the EU and international regulations. The application of weed control measures can be aided by the requirements of agricultural-environmental programmes and subsidies, the weed controlling effect of soil tillage, the expansion of reduced crop rotation with catch-crops with a beneficial effect on soil condition and weed control.

The reasons and factors mentioned above make the comparing analysis of different soil tillage systems useful.

According to this, the objectives of this research were 1. analysis of weediness changing as a result of different cultivation

methods, with emphasis to the various nutrition levels; 2. analysis of the effect of soil condition forming and changing as a

result of various tillage methods on the weediness, with new analytical methods;

3. determining whether the low tillage can be complied with the appropriate control of weeds;

4. reaction of some important weed species to the treatments; 5. conclusion on the basis of the results and formulating the

recommendations that can be used in practice.

Material and method

On the Experimental Station of the predecessor of title of the Szent István University (GATE) several different cultivation treatments were compared in a soil tillage trial on the basis of their effects on soil condition, yield and weediness. The significance of the examinations is increased by the judgement of the effects of tillage and fertilization and the introduction of catch-crops into the crop order.

The experimental field is in the Gödöllı hills. The soil (liable to sedimentation, sandy loam) and the precipitation conditions make the yield safety fluctuant, and the number of crops that can be cultivated economically is low. The year 2000 and 2002 were drier than the average, the years 1999 and 2001, on the other hand, had more rain.

In the two factorial, strip small plot trial with four replications (a) signifies the soil tillage methods, (b) the fertilization treatments. Plot sized are 5x20 m= 100m2. The order of crops is: white mustard in 1999, followed by winter wheat, after the harvest of wheat oil radish, maize in 2001, spring barley in 2002. The date of weed surveys is shown in Table 1. Table 2. includes the data of on the cropping practices in the trial.


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Table 1.: Dates of weed surveys (Gödöllı, D trial) Date of weed survey Year Crop

1 2 3

1999 white mustard 05. 27. 08. 22. (stubble)

2000 winter wheat 04. 20. 05. 16. 06. 16. 2000 oil radish 08. 24. 2001 corn 06. 06 08. 20 09. 27 2002 spring barley 04. 16. 05. 27. 07. 08

Treatments employed in the trial and their levels:

Soil tillage: a1: Ploughing (22-25cm): traditional system with several turns a2: Loosening (35-40cm) + disking (16-20cm): soil condition

improving system a3: Tillage system based on heavy cultivator (16-20cm), low-till and

low cost system a4: Direct drill: no-till, soil condition maintaining system

Fertilization in the autumn: b1: 80 kg N + 60 kg P2O5 + 60 kg K2O /ha active agent (low dose

according to the soil supply), b2: 160 kg N + 120 kg P2O5 + 120 kg K2O /ha active agent

(optimal dose according to the soil supply).

Table 2.: Cropping practices in the trial (Gödöllı 1998-2002)

Term 1999 2000 2000 2001 2002 Crop Objective Species Sowing time Harvest time Vegetation period, days Preceding crop

White mustard Mulch mixed 4. 12 6. 29. (stem.) 79 winter wheat

Winter wheat Grain Mv MAGVAS ’99. 10. 28. 7. 13. 258 white mustard

Oil radish Mulch mixed 8. 4. frozen (Oct) mulch 89 winter wheat

Maize Grain PR36R10 2001.5. 4. 2000. 10. 15. 143 oil radish

Spring barley Grain Amulet 2002.03. 22. 2002. 07. 03 104 maize

Tillage method Date of tillage Seedbed preparation Top-dressing Plant protection (weed control)

Pests, diseases

Ploughing 1998. 10. 28. 4. 10. - -

4 treatments 1999. 9. 28-29. 10. 8. 2000. 3. 23. 2000. 4. 24. Segal 65 WG - -

Disking 2000. 7. 17. 8. 4. - - -

3 treatments 2000 10.31. 2000.5.14 2001. 5. 18. Post: Titus plus - -

2 treatments 2002. 03. 16-19. 2002. 03. 21 2002.04. 12. - -

Number of plants/m2 a1 b1 a1 b2 a2 b1 a2 b2 a3 b1

165 162 160 156 158

460 566 504 575 480

102 111 110 120 110

64.300/ha 64.600 64.800 64.880 65.200

180 220 210 240 200

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a3 b2 a4 b1 a4 b2

162 160 162

570 310 390

116 102 112

65.300 63.600 63.900

210 150 190

Plot m2 5x20 = 100 100 100 100 100 100

Appearance of shoots Other:

1999. 04. 16. Without fertilization

1999 11. 20. Fertilization according to treatment 09. 18.

2000.08.10-15. residue nutrients

2001.05.12. fertilization according to treatments 2000. 10.31.

Residue nutrients

Methods of examination

Method of weed seed content analysis: On the stubble of the white mustard the upper 10 cm layer of the soil was analysed on the basis of ten 200 cm3 samples. Weed seeds were isolated with ZnCl2 sedimentation method. The size of the seed-bank determining the potential infection was determined for 1 m2.

Method of weed survey: Weed covering examinations were carried out with the 1 square meter (modified Balázs-Ujvárosi-type) quadrat method. In white mustard and its stubble coverage percentage was measured at ten places each time. Measurements were taken three times in winter wheat, maize and spring barley, and once in oil radish. Evaluation was carried out by variance analysis.

Method of yield evaluation: The yield data from the plots was calculated for one hectare. Data was evaluated by variance analysis.

Method of soil condition analysis: To measure soil resistance the Daróczi-Lelkes-type PENETRONIK penetrometer was used. The resistance of the upper 40 cm layer of the soil was measured every 5 cm, together with humidity.

Evaluation of the reaction of Ambrosia artemisiifolia L.: The different tillage methods were evaluated and placed in order on the basis of their Ambrosia artemisiifolia controlling effect.

Demonstration of the direct effect of soil resistance on weediness: The direct effect on soil resistance on weediness was demonstrated by rank correlation. Rank correlation was carried out according to the steps given by SVÁB (1981).

Results

1. Result of the seed content analysis From the samples taken from the stubble of white mustard it was seen

that the area is infected mainly by annual weeds. The composition of the seed-bank consisted mainly of T4-type species. Less seeds belonged to other annual and perennial species. Late summer annuals contribute to a diverse seed-bank in the soil (Table 3.). On the basis of the 20 species the soil is not


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considered rich in weeds. This tendency is apparent also on the field. The tillage systems, the simplified crop rotation and the employed agrotechnology (chemical plant protection) all contribute to the decrease of weed diversity. As for the life form of seed-bank species, the predominance of warm demanding species is obvious. Weed seed content per 1 m2 was 38250, infection is considered low.

Table 3.: Seed-bank of the soil, Gödöllı, 1999

Life form Number of species

Number of seeds

%

G1 1 3 0,39 G3 1 1 0,13 H3 2 4 0,52 H4 1 1 0,13 Perennials 5 9 1,18 T1 2 28 3,66 T3 1 1 0,13 T4 12 727 95,04

Annuals 15 756 98,82 Total 20 765 100

Results of the weed surveys In white mustard total coverage was average in May (9.31%). The

development of the species of the first aspect (7,14 %) were aided by the precipitation. T4 life form species that were characteristic of the area had many germinated plants, but their total coverage is low (1.66 %). Annuals contributed to the 98% of the total weed coverage. On the stubble of mustard weed coverage was much higher (71,02 %)compared to the spring results. Germination after harvest was significant with its 8.1%, and was the fourth in the order. This means that the time of mulching of the protective crop and the tillage for the following crop has to be chosen more carefully in case of wet weather than in an average vegetation period. The development of T4 species forming the third aspect (58.71 %) was aided by high precipitation and high temperature. There were three monocotyledonous weeds present (Digitaria sanguinalis, Echinochloa crus-galli, Elymus repens). Their total coverage is 9.23 %, from which perennials presented 1.32 %. The proportion of monocotylednonous plants in the total coverage increased from the initial 2.15% to 13%, with Digitaria sanguinalis and Echinochloa crus-galli playing a significant role. The number of species was 19 and 28 at the two dates.

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In April in winter wheat the weeds of the T1 group dominated in accordance with the date of the survey. The formerly typical cereal weeds had a low cover percentage. Due to the favourable weather conditions, the lack of many competitors, and the slower development of the wheat, many germinated T4 plants were found. From among monocotyledonous weeds, Echinochloa crus-galli was significant. The scope of the presence of T4 weeds is in accordance with the other experiences in the country, and warns about the tendency and the necessity of creating a proper crop rotation. In case plant protection was not effective against these species, in next year’s intertilled crop the weed problem may increase.

Since total coverage consisted in large part of species sensitive to the applied active agents, the sensitive and early annuals thinned or disappeared by May.

By June perennials – especially Elymus repens – had the highest coverage, but differently at the two nutrient levels. Their role in total coverage and in determining the differences between tillage methods is similar to the role of annuals in April.

Considering the June data it can be said that if nutrition is unfavourable, tillage methods without soil-turning may prove to be weed-promoting. On the other hand, if nutrition is appropriate, the disadvantage of these tillage methods disappears. The effect of direct drill is antinomic, according to the literature, because both its weed controlling and weed promoting effect was seen.

It is favourable that the coverage of perennials is not too high and their upsurgence in maize is less expected. Within total coverage the proportion of monocotyledonous plants was rising.

Because of the dry vegetation period wheat did not tiller properly, and therefore its weed-limiting effect was less. It is probable that this was the reason why the weed-controlling effect of ploughing could not manifest.

On the basis of the survey taken in oil radish the predominance of E. crus-galli was obvious compared to annuals and the total coverage, at optimal nutrition level. In the average of the four treatments annual monocotyledonous plants contributed to 74.99% of the total coverage. E. crus-galli has a special significance, because maize was following oil radish.

In maize Echinochloa crus-galli had a high coverage at the time of the first survey; compared to the others, with the exception of cultivator treatment on low nutrition level where the coverage of Elymus repens was close to 4%. Because of the late survey, in the case of the other species more T4 weeds appeared.

At the time of the second survey the coverage was tenfold. E. crus-galli was again the first. A Digitaria sanguinalis, which was missing in June, climbed to the second place. The coverage of Ambrosia artemisiifolia also


17

increased, just like the cover percentage of E. repens and Convolvulus arvensis.

By September the weed coverage decreased. Many weeds finished their life activity and the shadowing of the maize was also acceptable. E. crus-galli still had a high coverage, but shared its place with the formerly insignificant Solanum nigrum and A. artemisiifolia.

The spring barley was lacking weeds, which was caused probably by the low precipitation and the coverage of barley. At the time of the late survey mainly perennials (E. repens) and T1 species were present, with S. media as the most characteristic. The adaptability of A. artemisiifolia is obvious, since young plants were seen even at this date.

By the time of the second survey the field still had low weed coverage, with the exception of direct drill treatment with higher nutrition level. T4 life forms gained prevalence, with E. crus-galli having the highest coverage. A. artemisiifolia had an almost similar coverage in the cultivator treatment at optimal nutrition level.

In July after the harvest the coverage was obviously low, but E. crus-galli still had the highest coverage.

It can be stated that in the weed population that is poor in species T4 weeds had the highest significance. This is probably the result of the cultvation practice of the previous years.

As a result of the weed condition after white mustard sown as an adjusting crop, the effect of the treatments can be evaluated reliably in winter wheat. In April and June the interaction of the two factors was apparent, so nutrition influenced the weed limiting or promoting effect of the cultivation treatments.

At the first date the disking + loosening combination limited the development of annuals better than cultivator treatment at low nutrition level. Since total coverage was determined by annuals this was also true for total coverage. In case of higher nutrition level weed coverage was higher in treatments without soil turn, but the difference is not significant, which means nutrition had a balancing effect.

Weed condition in May was influenced by herbicide treatment to such an extent that the interaction of treatments and the weed-promoting effect cannot be demonstrated.

According to the results in June the wed limiting effect of ploughing is just tendential at minimal nutrition level. Nutrition modifies this and in case of optimal fertilizer level the other treatments curb weeds more than direct drill.

Tillage preceding the sowing of oil radish and the development of oil radish balanced the weed condition. The weed limiting effect of ploughing

Aniko Farkas

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was obvious at both nutrition levels. The tillage accompanying the sowing of oil radish had an effect on weediness also later.

In maize the interaction of the tillage and fertilizer treatments could not be demonstrated. It is obvious that the weed limiting effect of ploughing could be demonstrated in the average of the three dates. The other treatments had a different effect depending on the level of nutrition but statistically this effect is not authentic.

In barley the weed limiting effect of ploughing and the weed promoting effect of direct drill is showing a tendency.

The most significant weed of our days, Ambrosia artemisiifolia L was evaluated separately. Its coverage was considerable at both nutrition levels. In winter wheat and maize it had tendentially higher coverage on soils with proper nutrition supply. On the other hand, depending on the year, it utilized low level nutrients better than competitive weeds and the crop. This shows that A. artemisiifolia can be limited by appropriate fertilization and the cultivation of weed limiting crops. This is in accordance with the demand for harmony between resources.

Between the different tillage treatments the favourable or unfavourable effect on the weed cannot be determined. In the order of treatments the ploughed soil was the most favourable for A. artemisiifolia. This means that on the weed-infected field the weed-bank of the soil also aids the proliferation of the weed through annual ploughing.

2. Yield results

Examinations were carried out in biologically favourable crop rotation system. The crop order of the trial is not typical because of the introduction of oil radish. Therefore the results can be used also from the viewpoint of sustainable crop production and integrated technologies.

The yield was the best in case of soil loosened favourably 35-45 cm deep, independently from the weather of the year. Somewhat lower yield was harvested from soil tilled with cultivator, and ploughing was the third in order. In every case the yield was lowest in direct drill treatment. On similar soils, where direct drill can be favourable because of its soil protecting function, the lower yield and its effect of weediness call for careful consideration. In case of professional and continuous chemical protection weediness can be reduced, and this may have environmental consequences. The weed limiting effect of loosening is not satisfactory, with the exception of perennial weeds, but its favourable effect on the soil provides an economic advantage of ploughing, that has otherwise a better weed limiting effect.

In winter wheat and spring barley the interaction of the two factors is not apparent, but fertilization had yield increasing effect in all treatments,


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most strongly in loosening + disking treatment. The drough damage lessening effect of fertilization was demonstrated in accordance with literature.

The undisturbed soil condition characteristic of direct drill did not limit the favourable utilization of fertilizers in case of maize, in a year with average precipitation. It can be stated that the yield limiting effect of compacted or sedimented soil condition can be reduced.

3. Effect of introducing a catch crop between the main crops

The favourable biological effect of crop rotation was increased both by white mustard and oil radish. Favourable effect was shown in the better cultivability of the soil. On given soil that is susceptible to sedimentation the duration of soil loosening is short and the effect can be lengthened by crops with a loosening effect.

4. Change of soil condition A compacted layer forms under the layer of annual ploughing, which

can extend also towards the upper layers. The loosening effect of oil radish improved the soil condition, and this effect was shown also in the deeper layers. Under the depth of the basic tillage for the next crop (maize) the penetration values were higher but the thickness of the plough-sole decreased.

The flaws of the previous years were demonstrated mainly in the shallow tillage treatments. The 35-45 cm deep loosening of the soil alleviated this problem, and no soil resistance above 3 MPa (critical value) was measured. The loosening effect of oil radish was reduced somewhat by the disking following loosening.

In soil tilled with cultivator a more compacted layer formed under the layer in question. The loosening effect of oil radish could be shown down to 25 cm depth.

In direct drill plough-sole shows the previous soil-turning tillages. In the second year the soil is compacted under the sowing, in the upper 10 cm of the soil. The loosening effect of oil radish was demonstrated only in the upper 15 cm layer but this effect disappeared in the next year. It is important that weeds endure compacted soil condition while in case of cultivated crops the yield is depressed because of the competition and the limiting effect on rooting.

5. Results of rank correlation

The basic hypothesis of my work was that the soil condition influences the development of the weeds and plant organisms directly. It was assumed that in a certain depth soil condition affects weediness. If treatments are put in order on the basis of MPa values measured in ascertain depth,

Aniko Farkas

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weediness is related to this order. According to the calculated values of the rank correlation the connection of the two orders of the treatments can be demonstrated only in a few cases. This can be due to the fact that treatments change the looseness of the soil in different depths and extents and in a crop the different plant populations are presented in different proportions, thus affecting the order and rank correlation also. On this basis the analysis of pure stands with different tillage methods is recommended.

Examining the rank correlation in function with the depth certain laws can be observed. To determine mathemaical relationship a dot diagram was created, fitting the sixth degree polinom of EXCEL as a trend line. Different R2 values were calculated for the different dates and weed groups, but those show the strong fit of the polinom. The example is shown on the weed and soil conditions of winter wheat in Table 4. Table 4.: Rank correlation depending on sample depth, Gödöllı

R2

Winter wheat 2000 April May June rankcor1

* 0,93 0,36 0,78 rankcor2

** Annual 0,82 0,91 0,98

rankcor1 0,89 0,91 0,91 rankcor2

Perennial 0,83 0,91 0,63

rankcor1 0,75 0,86 0,97 rankcor2

All 0,88 0,83 0,63

Key:* at minimal nutrition level, ** at optimal nutrition level

It can be seen in Table 4. that the value calculated on the basis of the coverage of annual weeds in winter wheat in May is low. This is in accordance with the fact that because of the chemical plant protection annuals are almost gone from the field. Among “unnatural” conditions this law does not manifest. In June the value of perennials and total coverage is average, this is probably due to the fact that the role perennials played in total coverage is different in each treatment.

The results justify the necessity of other, similar examinations, despite the difficulties.

6. New scientific results On the basis of the analyses of tillage, soil condition and weediness the following new scietific results were determined. 1. On Gödöllı brown soil the relationship between the favourable loosening of the root zone and the yield was obvious in dry year. The soil condition created by ploughing ensures average yield. 2. On soil that is prone to sedimentation the yield reducing effect of direct drill in winter wheat, maize and spring barley was caused by bad soil condition and the higher coverage of less susceptible weeds.


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3. Tillage methods were put into order according to their weed-limiting effect. The weed promoting effect of direct drill and the weed limiting effect of regular soil-turning was proved together with the modifying effect of crop rotation order and nutrition level, especially in the case of tillage without soil-turning (loosening, cultivator treatment, disking). 4. On the basis of the decreasing coverage of Ambrosia artemisiifolia L. ploughing was put to the first rank as the most favourable tillage method for the development of the species. The great competitiveness of A. artemisiifolia had a tendency, especially among low nutrition conditions. 5. Analyses carried out during the 4 years of the experiment made rank correlation possible. It was determined that the method can be further improved by calculations per species. Since the competition of species is seen among cultivation conditions, pure stands and more tillage methods can be taken into account. 6. The dependence of rank correlation on tillage depth was proven by fitting a polinom. More analyses are necessary to justify or reject the accuracy of the method.

Summary

The hypothesis was that soil condition affects weeds as plants

directly. The competition for nutrients also influences the predominance of plant potential. As a result appropriate soil management can avert not only the further deterioration of our soils but weeds can also be forced back. The significance of the research is increased by the examination of protecting intercrops. The introduction of these plants (originally used as green manure) enables the biological improvement of soils and weed control. Special attention was given to the adaptation ability of Ambrosia artemisiifolia. New methods were employed together with weed surveys and soil resistance measurements. On the basis of rank correlation other relationships could be discerned.

The growing probability of the more frequent drought years and the tendency of extreme weather indicate the necessity of tillage systems that increase the water absorbing capacity of the soil and that retain the water.

Tillage systems that improve and maintain soil condition should get into the foreground. The coverage of soil between two main crops also becomes necessary, and the introduction of crops having a beneficial effect on soil and yield into the crop rotation also.

The effect of the tillage used in the previous years can be demonstrated and thus the methods for improvement can be planned and carried out. The damage can be alleviated by tillage and biological methods. The disk-sole appearing because of the stubble-clearing of white mustard

Aniko Farkas

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showed the importance of adaptation to the water content of the soil. To eliminate the compaction of soil near the surface all tillage methods (with the exception of direct drilling) were sufficient, thus presenting several possibilities to improve lesser damages. The loosening effect of the roots of oil radish was missing in case of direct drilling, which shows that the plant is susceptible of soil condition.

The importance of good soil condition and nutrition in the reduction of drought losses was demonstrated again. Yield was affected most favourable by 35-45 cm deep loosening. In dry vegetation period besides loosening methods that spared the soil structure (cultivator) also had a favourable effect. On the soil of the experimental area the yield reducing effect of direct drilling in wheat and maize can be explained by weeds and the blocking of water transport.

The yield of maize following oil radish went according to the loosening of soil and its nutrient supply. The yield of maize was influenced more by the water retaining capacity of the soil than by the precipitation in the vegetation period. The undisturbed soil condition of direct drilling did not hinder the utilization of fertilization in case of maize in a year with average precipitation. It can be stated that in case of good nutrition supply the yield reducing effect of compacted or sedimented soil can be diminished.

The mustard in the crop rotation had a favourable effect. By mulching at the appropriate time we can avoid the weed-promoting effect of the intercrop and the unnecessary water loss. The greater weed coverage in the summer periods was promoted by the favourable loose condition and the water content of the soil, and this way plant protection measures could be timed and the weed seed base decreased.

The soil loosening effect of oil radish was proved by soil resistance values. It can be employed as protecting crop in dry years if the reduction of soil water loss is emphasized during the sowing. Oil radish improved the cultivability and ensured a good green crop effect.

The direct drilling has a weed promoting effect, while ploughing reduces the weeds. Tillage methods that do not turn the soil (loosening, cultivator, disk tillage) have different weed promoting or prohibiting effects in case of the various plants and nutrition levels.

The development of the Ambrosia artemisiifolia is the best among conditions created by ploughing (the dormant seeds get into the germination zone). The great competition ability of Ambrosia artemisiifolia has a tendency for having a greater coverage in case of lower nutrition level. In case of better nutrition the weed-limiting effect of cultivated crops is higher, and plant protection is easier to apply.


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The accuracy of the rank correlation method still needs further analysis. In the future the evaluation of “pure” weed stands and the analysis of data separated according to species and life forms are expected.

Acknowledgements. The research programs supported by OTKA 32851 and OTKA 34274

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FARKASNÉ SZERLETICS A. 2004. Kettıs termesztés, köztes termesztés, köztes növény elnevezések és használatuk. XLVI. Georgikon Napok, Keszthely, 2004. szept. 16-17. CD kiadvány, ISBN 963 9096 962

FARKASNÉ SZERLETICS A. 2004. Olajretek alkalmazása védınövényként gödöllıi barna erdıtalajon. XLVI. Georgikon Napok, Keszthely, 2004. szept. 16-17. CD kiadvány, ISBN 963 9096 962

Herbologia Vol. 7, No. 1, 2006.

RESISTANCE STUDY OF AMARANTHUS RETROFLEXUS L. SPECIES POPULATION TO THE HERBICIDE IMAZETHAPYR

Branko Konstantinović, Maja Meseldžija, Dragana Šunjka

Faculty of Agriculture, Trg Dositeja Obradovica 8, Novi Sad, Serbia and Montenegro

E-mail: [email protected]

Abstract Use of herbicides and lack of alternative methods of weed control in

conditions of intensive agricultural production have created convenient environment for herbicide resistant weed species development. Permanent use of herbicides belonging to the group ALS inhibitors, especially imidazolinones and sulfonylureas, led to resistance occurrence of weed species to this herbicide group. During two years (2005-2006) resistance of weed species Amaranthus retroflexus L. to ALS inhibitors was studied. From different localities in Vojvodina, i.e. Krivaja, Kikinda and Becej, with a long history of ALS inhibitors use in weed control, seed of plants for which there exist possibility of resistance occurrence to herbicide imazethapyr was collected. Studies were performed by two methodic procedures, by Petri dish assays (Clay and Underwood, 1990) and by whole plant studies (Moss, 1995). In the trials, as a susceptible standard herbicide free population of Amaranthus retroflexus L. from ruderal sites that was used. Results of the assay are given in the reaction curve, and resistance index is determined in regard to the susceptible referent population. By comparative analysis, resistance occurrence of weed biotype Amaranthus retroflexus L. from the locality Krivaja has been established, whereas populations from localities Becej and Kikinda remained susceptible to the mode of action of the studied herbicide belonging to the ALS inhibitor group.

Key words: Amaranthus retroflexus L., ALS inhibitors, imazethapyr, herbicide resistance.

Introduction

Nowadays herbicides belonging to the group of ALS inhibitors such

as sulfonylureas, imidazolinones, triazolopyirimidines, pyrimidinylthio- benzoates and sulfonylamino-carbonil-triazoles represent extremely significant herbicides for weed control in many crops (Wagner et al., 2002). Their permanent use during three years period, or longer, resulted in evolution of ALS resistant biotypes in the world (Thill et al., 1991; Powles

B. Konstantinović et al.

32

and Shaner, 2001; Rashid et al., 2003; Rubin et al., 2004) and in Vojvodina (Konstantinovic et al., 2003a; 2003b; 2003c). Primary action target site of these herbicides is the enzyme of acetolactate synthase that participate in biosynthesis of amino acids isoleucine, leucine and valine (Ray, 1984; Gerwick et al., 1990; Takahashi et al., 1991, Babczinski, 2002), and resistance develops as the consequence of the single mutation points that ALS structure makes less susceptible to herbicides. After five years of permanent use of the ALS inhibiting herbicides in monoculture of Triticum aestivum L. crop (Mallory-Smith et al., 1990) in 1987 the first weed resistant to ALS inhibitors, Lactuca serriola (Smith and Cairns, 2001) was determined. Stellaria media (L.) Vill (Kudsk et al., 1995) was the first weed species resistant to Sulfonylureas found in Europe. Until now, resistance has been described for 93 weed biotypes from all over the world, and this number is constantly increasing (Heap, 2006). In regard to the other herbicide groups, weed biotypes resistant to herbicide that inhibit ALS enzyme are the most numerous. In the paper the occurrence of herbicide resistance development of the weed species Amaranthus retroflexus L. from various localities in Vojvodina to herbicide imazethapyr from the chemical family Imidazolinones. On the studied localities Imidazolinones had long history of use in weed control.

Material and methods

During 2005 and 2006 study of weed species Amaranthus retroflexus L. resistance to imazethapyr was performed according to the methods applied in laboratory conditions and climatic chamber (Clay and Underwood, 1990; Moss, 1995). In bioassays a range of imazethapyr rates were used, e.g. 0 , 0.04 , 0.08 , 0.10 , 0.15 , 0.20 and 0.40 kg a.i./l. During assays seedling epicotyls and hypocotyls length, stem height, foliage fresh weights and seed germination and shooting were measured. Statistical data processing was performed by variance analysis (ANOVA), and significant difference was evaluated by t-test (Hadzivukovic, 1991). Resistance can be determined only if there are statistically significant differences between the studied population and the susceptible standard and if resistant population can not be controlled by herbicide rate that is efficient in control of the susceptible one (Beckie et all., 2000). Results of the measured parameters – epicotyls and hypocotyls length, stem height and germination percentage and shooting are presented as a quantity-response curve, while values of the foliage fresh weight and resistance indices were given in a table.

Resistance study of A. retroflexus L. species population to the herbicide imazethapyr

33

Results

Statistical analysis results of epicotyls and hypocotyls shoots length, stem height and foliage fresh weight (t test) are given in Table 1. Analysis of imazethapyr effect to the measured biological parameters of the species Amaranthus retroflexus L. showed that there are statistically significant differences (p< 0.05) between values of the measured parameters of populations from locality Krivaja and population used as a susceptible standard (S). Tab. 1. Significant difference between Amaranthus retroflexus L. populations

from the studied localities and susceptible standard treated by imazethapyr

Parameters Localities

Epicotyl length

Hypocotyl

length

Stem height

Foliage fresh

weight Krivaja - S * * * * Kikinda - S N.Z. N.Z. N.Z. N.Z. Bečej - S N.Z. N.Z. N.Z. N.Z.

p<0,05* N.Z. – statistically non-significant difference

0

10

20

30

40

50

60

70

80

0 0,04 0,08 0,1 0,15 0,2 0,4

kg a.m. imazetapir/lkg a.i. imazethapyr/l

proc

enat

klij

avos

tige

rmin

atio

n %

Krivaja

Kikinda

Bečej

Ruderallnostaniste/ruderal site

Fig. 1. Effect of the herbicide imazethapyr to


34

Amaranthus retroflexus L. seed germination Effect of the herbicide imazethapyr to seed germination of weed species Amaranthus retroflexus L. is given in the Graph 1. The highest percentage of germinated seeds was established for population from locality Krivaja. Population of the susceptible standard and localities Kikinda and Becej had very low germination capability with all applied herbicide rates.

0

5

10

15

20

25

00.0

40.0

8 0.1 0.15 0.2 0.4

kg a.m. imazetapir/lkg. a.i. imazethapyr/l

duzi

na e

piko

tila

(mm

) ep

ycot

yl le

ngth

(m

m)

Krivaja

Kikinda

Bečej

Ruderalnostaniste/ruderalsite

Fig. 2. Effect of the herbicide imazethapyr to Amaranthus retroflexus L. epycotyl seedlings length


35

0

5

10

15

20

0 0.04 0.08 0.1 0.15 0.2 0.4kg a.m. imazetapir/lkg a.i. imazethapyr/l

du

zin

a h

ipo

koti

la (

mm

)h

ypo

coty

l len

gth

(m

m)

Krivaja

Kikinda

Bečej

Ruderalnostaniste/ruderal site

Fig. 3. Effect of the herbicide imazethapyr to Amaranthus retroflexus L. hypocotyl seedlings length

By statistical analysis (Table 1) of the values for epicotyls and hypocotyls length, significant difference was determined for populations from locality Krivaja in regard to the other studied localities and population of the susceptible standard. Populations values from localities Kikinda and Becej did not show significant differences from those obtained for the susceptible standard. Values for epicotyls and hypocotyls length are presented in Graphs 2 and 3.

0

20

40

60

80

100

120

0 0.04 0.08 0.1 0.15 0.2 0.4

kg a.m. imazetapir/lkg a.i. imazethapyr/l

pro

cen

at n

ican

ja%

of

sho

oti

ng

Krivaja

Kikinda

Bečej


Fig. 4. Effect of the herbicide imazethapyr to shooting of

Amaranthus retroflexus L. plants


36

Effect of the herbicide imazethapyr to shooting of plants is given in Graph 1. Percentage of emerged plants from the site Krivaja was the highest.

0

5

10

15

20

25

30

35

0 0.04 0.08 0.1 0.15 0.2 0.4kg a.m. imazetapir/lkg a.i. imazethapyr/l

visi

na

stab

la (

mm

) s

tem

hei

gh

t (m

m)

Krivaja

Kikinda

Bečej


Fig. 5. Effect of the herbicide imazethapyr to the height Amaranthus retroflexus L. stems.

Values of the studied parameters of Amaranthus retroflexus L. biotype plants from locality Krivaja showed statistical significant difference (p< 0.05) in regard to the susceptible standard and other studied localities. Between biotypes from localities Kikinda and Becej there were no statistically significant differences, nor there were differences in regard to the susceptible standard (Graph 4). Resistance level based upon foliage fresh weight was determined according to the scale by Moss et al (1999) that imply several possible resistance levels of the studied population (Table 2).

Tab. 2. Resistance level of the studied populations of Amaranthus retroflexus L. determined according to the scale by Moss, based upon the fresh weight.

Locality Resistance level

Krivaja 4* Kikinda 1* Bečej S

S - osetljivost na primenjeni herbicid/susceptibility to the applied herbicide 1* – rana indikacija rezistentnosti, mogućnost da je došlo do redukcije delovanja herbicida/early indication of the resistance, suspected herbicide reduction


37

2*/3* - potvrñena rezistentnost, mogućnost da je došlo i do redukcije delovanja herbicida/confirmed resistance, suspected herbicide reduction 5*/4* - potvrñena rezistentnost, mala verovatnoća lošeg delovanja herbicida-comfirmed resistance/reduced likelihood of low herbicide action.

Tab. 3. Resistance level of the studied populations of Amaranthus

retroflexus L. given in resistance index Resistance index

Locality epicotyl hypocotyl stem height foliage fresh weight Krivaja 1.8 1.61 1.0 2.27 Kikinda 1.0 0.8 0.9 0.53 Bečej 1.0 1.0 1.0 0.99

The highest values of resistance index of the measured parameters were determined for population from the locality Krivaja (1.0 – 2.27). The values of resistance index for population of Amaranthus retroflexus L. from localities Kikinda and Becej were significantly lower, i.e. less than 1.

Discussion

Determined significant differences in germination (Fig. 1) and values for epicotyls and hypocotyls length (Fig. 2 and 3) between biotype from locality Krivaja and susceptible standard, as well as other studied localities implied high resistance of this biotype to the herbicide imazethapyr. It was also determined that decay of seedlings from localities Kikinda and Becej occurred at rates above 0.08 kg a.i. imazethapyr/l, while seedlings from localities Krivaja at rate of 0.40 kg a.i. imazethapyr/l remained well developed. Seedlings from ruderal site, used as the susceptible standard completely decayed at a rate of 0.04 kg. a.i. imazethapyr/l. In regard to susceptible standard and localities Kikinda and Becej, increased rates of the applied herbicide caused the lowest reduction in epicotyls and hypocotyls length of weed species Amaranthus retroflexus L. biotype from locality Krivaja. Imazethapyr effect to weed species Amaranthus retroflexus L. biotypes evinced in differences in plant emergence and stem height (Fig. 4 and 5). In all applied imazethapyr rates, the highest percentage of emerged plants (100%), as well as the highest values for the stem height was determined for biotype from locality Krivaja. Decay of plants from this locality did not occur even with applied rate of 0.40 kg a.i. imazethapyr/l. Based upon measured biological parameters, samples of the susceptible standard, as well as plants from localities Kikinda and Becej, remained


38

susceptible to herbicide imazethapyr action, for decay occurred after application of the second rate of 0.08 kg a.i. imazethapyr/l. Based upon resistance level obtained by foliage fresh weight measurement (Table 2), resistance was confirmed for populations from locality Krivaja (4*), with a slight probability that herbicide showed low efficiency. For biotype from locality Kikinda an early indication of resistance was determined, but with a possibility of herbicide efficiency reduction. Population from locality Becej remained susceptible to the applied herbicide. Resistance index of all measured parameters (Table 3) suggests that biotype from the locality Krivaja acquired the highest resistance to the applied rates of the herbicide imazethapir. Populations from locality Becej (IR = 0.99 - 1) and Kikinda (IR = 0.53 – 1) showed high susceptibility to herbicide imazethapyr.

Conclusion

Based upon results of the resistance studies of different populations of the weed species Amaranthus retroflexus L. to herbicide imazethapyr, it can be concluded that intensive use of ALS inhibiting herbicides caused reduced susceptibility of weed species Amaranthus retroflexus L. population to imazethapyr. The biotype from the site Krivaja showed the highest resistance to the applied rates of herbicide imazethapyr. Biotype from the locality Becej showed reduced susceptibility to the applied herbicide (RI = 0.99 – 1.0). The highest susceptibility to the applied rates of the herbicide imazethapyr was found in the biotype from Kikinda (RI = 0.53 – 1.0).

References BABCZINSKI, P. (2002): Discovery of the lead structure for propoxycarbazone -sodium (BAY

MKH 6561). Pflanzenschutz-Nachrichten-Bayer 55, p. 5-14. BECKIE, H.J., HEAP, J.M., SMEDA, R.J., HALL , L.M. (2000): Screening for Herbicide

Resistance in Weeds. Weed Technology, 14, p. 428-445. CLAY , D.V. & UNDERWOOD, C. (1990): The identification of triazine and paraquat resistant

weed biotypes and their response to other herbicides. Importance and perspectives on herbicide resistant weeds, Luxemburg. p. 47-55.

GERWICK, C.M., SUBRAMANIAN , M.V. AND LONEY-GALLANT , V.I. (1990): Mechanism of action of the 1,2,4,-triazolo[1,5-]pyrimidines. Pesticide Science, 29, p. 357-364.

HADŽIVUKOVI Ć, S. (1991): Statistički metodi s primenom u poljoprivrednim i biološkim istraživanjima. Poljoprivredni fakultet, Novi Sad.

HEAP, I. (2006): International survey of herbicide resistant weeds. Online internet, www.weedscience.com

KONSANTINOVIĆ, B., MESELDŽIJA, M., ŠUNJKA, D., KONSTANTINOVIĆ, BO. (2003a): Determination of resistant biotypes of Amaranthus retroflexus L. on ALS inhibitors. 3rd International Plant Protection Symposium at Debrecen University, Debrecen Hungary, p. 269-276.


39

KONSTANTINOVIĆ, B., MESELDŽIJA, M., POPOVIĆ, S., KONSTANTINOVIĆ, BO. (2003b): Study of resistance to ALS inhibitors in the weed species Echinochloa crus-galli L., The BCPC International Congress, Glasgow, Scotland, UK, Vol. 2, p. 771-775.

KONSTANTINOVIĆ, B., MESELDŽIJA, M., ŠUNJKA, D. (2003c): Ispitivanje rezistentnosti korovske vrste Echinochloa crus-galli L. na ALS inhibitore, Zbornik referata 2. savetovanja o korovima, Sarajevo, 6-7 juni 2003.

KUDSK, P., MATHIASSEN, S.K. AND COTTERMAN, J.C. (1995) Sulfonylurea resistance in Stellaria media (L.) Vill. Weed Research, 35, p. 1924.

MALLORY-SMITH , C.A., THILL , D.C.& DIAL , M.J. (1990): Identification of sulfonilurea herbicide-resistant prickly lettuce (Lactuca seriola). Weed Technology, 4, p. 163-168.

MOSS, S.R. (1995): Techiniques for determinig herbicide resistance. Proceedings of the Brighton Crop Protection Conference-Weeds, p. 547-556.

POWLES, S. B. & SHANER, D.L. EDS. (2001): Herbicide resistance in world grains. CRC Press, Boca Raton, Florida, USA. p. 308.

RASHID, A., NEWMAN, J.C., O'DONOVAN, J.T., ROBINSON, D., MAURICE, D., POISSON, D. AND

HALL , L.M. (2003): Sulfonylurea herbicide resistance in Sonchus asper biotypes in Alberta, Canada. Weed Research, Volume 43, p. 214-221.

RAY , T.B.(1984): Site of action of chlorsulfuron. Plant Physiology, 75, p.827-831. RUBIN, B., TAL, A. AND YASUOR, H. (2004): The significance and impact of herbicide

resistant weeds – a global overveiw. Acta Herbologica, 13, p. 277-288. SHANER, D.L., ANDERSON, P.C. AND STIDHAM , M.A. (1984): Imidazolinones: potent

inhibitors of acethydroxyacid synthase. Plant Physiology, 76, p. 545-546. SMIT, J.J. AND CAIRNS, A.L.P. (2001): Resistance of Raphanus raphanistrum in the Republic

of South Africa. Weed Research, 41, p. 41-47. TAKAHASHI , S., SHIGEMATSU, S. AND MORITA, A. (1991): KIH-2031, a new herbicide for

cotton. Proc. Brighton Crop Prot. Conf., p. 57-62. THILL , D.C., MALLORY-SMITH , C.A., SAARI, L.L., COTTERMAN, J.C., PRIMIANI , M.M., AND

SALADINI , J.L. (1991) Sulfonylurea herbicide resistant weeds: discovery, distribution, biology, mechanism and management. In: Herbicide Resistance in Weeds and Crops (eds JC Caseley, GW Cussans & RK Atkin), 115128. Butterworth-Heinemann, Oxford.

WAGNER, J., HAAS, H.U. AND HURLE, K. (2002): Identification of ALS inhibitor-resistant Amaranthus Biotypes using polymerase chain reaction amplification of specific alleles. Weed Research, 42, p. 208-287.


INFLUENCE OF THE ADJUVANT DESH ON THE EFFICACY AND

SELECTIVITY OF IMAZAMOX 40 a.i.L-1

(PULSAR 40) IN THREE PERENNIAL LEGUME CROPS

Tsvetanka Dimitrova1, Senka Milanova

2

1Institute of Forage Crops, 5800 Pleven [email protected]

2Institute of Plant Protection, 2230 Kostinbrod [email protected]

Abstract

During the period 2003-2005 a study was conducted on slightly

leached chernozem with the purpose of studying the influence of the adjuvant Desh on the efficacy and selectivity of Imazamox 49 a.i.L-1 (Pulsar 40) in lucerne (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.) and sainfoin (Onobrychis vicifolia Scop.). It was found that:

The herbicide Imazamox 40 a.i.L -1 (Pulsar 40) at the rate of 20 ml a.i.ha-1 in combination with the adjuvant Desh – 1000 ml a.i. ha-1 applied in early growing season of lucerne, birdsfoot trefoil and sainfoin had high selectivity and herbicidal efficacity reaching 93-97%;

Treatment of swards of perennial legume crops improved their botanical composition and increased dry biomass productivity 1.4 to 2.8 times. Key words: Imazamox 40 a.i.L-1, adjuvant Desh, weeds, productivity, perennial legume crops.

Introduction

Economic importance of the perennial legume crops including lucerne (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.) and sainfoin (Onobrychis vicifolia Scop.) is many-sided. They are valuable for the high biological value of their forage, as well as in an ecological aspect improving soil fertility and phytosanitary state.

Weed competition is one of the main factors causing quick thinning of the swards of these species, reducing and worsening quality of their production. This circumstance is of decisive importance for weed control during the period after establishment of the stands of these herbaceous species. Although the chemical method of controlling weeds in the swards of the above-mentioned species is considered efficient by some authors, the studies are limited in this field (Benkov & Prodanov, 1975; Dimitrova, 1987 and 1995; Lescar Audy, 1971).

The out-of-vegetation treatment of lucerne with Imazethapyr 100

Tsvetanka Dimitrova and Senka Milanova

42

a.i.L-1 (Speed 10 SL) resulted in 90.8 % biological efficacy, increase of dry biomass and crude protein yield of 60 % and 2.4 to 2.6 % respectively and decrease of fibre content of 3.8 to 4.1 % (Dimitrova, 2001). The chemical weed control proved to be the most efficient in pure lucerne growing for forage, the net income of its application increasing by 64.8 % (Stoykova & Dimitrova, 2005).

The long and unilateral use of the same herbicides resulted in selection of genetically resistant weeds (Nikolova & Konstantinov, 1989; Beckie et al., 2000; Lee & Owen, 2000). Resistance has been reported for most herbicide categories and at least for 174 weed species (Heap, 2004). This circumstance necessitates study of new approaches to using herbicides, new active substances, optimimization of their doses. Some authors reported that the adjuvants to the herbicidal solutions led to an increase of their efficacy and to reduction of the doses (Kudsk & Streibig, 2002; Dogan et al., 2002).

Imazamox belongs to the imidazolinone class that includes imazapyr, imazapic, imazethapyr, imazamox and imazametabenz. The herbicides of the group of imidazolinones and sulphonylureas kill the weeds by inhibiting acetolactate synthase (ALS). The imidazolinone herbicides possess high biological efficacy at low application rates and are an attractive alternative for weed control in lines of spring wheat resistant to the imidazolinone group (Pozniak et al., 2004), winter wheat (Stougaard et al., 2004). Resistance to imazamox has also been introduced into cultivated sunflower by traditional breeding methods (Massinga et al., 2005). Herbicide-resistant rape prevails on the rape market in Canada with imidazoline-resistant canola (IPI) with 50:50 combination of imazamox and imazethapyr (Karker et al., 2004). Due to the great biological activity of imazamox it is very important to know the possibility for dose decrease. The interest for application of reduced rates of herbicides is in favor of the farmers and environment. The adjuvants can stimulate the herbicide uptake and provide a possibility for dose reduction (Mathiassen & Kudsk, 2002; Kieloch & Domaradzki, 2005).

The objective of this study was to investigate the influence of the adjuvant Desh on the efficacy and selectivity of Imazamox 40 a.i.L-1 (Pulsar 40) in lucerne (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.) and sainfoin (Onobrychis vicifolia Scop.).

Material and methods

The study was conducted during the period 2003-2005 at the experimental field of the Institute of Forage Crops in Pleven on slightly leached chermozem. The variants presented in Table 1 were laid out three times by years in established stands of lucerne, birdsfoot trefoil and sainfoin.

Influence of the adjuvant Desh on the efficacy and selectivity of imazamox 40 a.i. l-1 (Pulsar)

43

The block method was used with three replications and harvest plot size of 20 m2.

Natural background of weed infestation was used. The predominant weed species were also main weeds in the old swards of the above-mentioned crops: Capsella bursa pastoris L., Thlaspi arvense L., Stellaria media L., Veronica hederifolia L., Anagalis arvensis.

The treatment was made with 400 l ha-1 working solution in early growing season. The adjuvant Desh was added immediately before the treatment. The following characteristics were observed: selectivity (after EWRS scale); degree of weed infestation (by the quantity and quantity-weight method); herbicidal efficacy, %; dry biomass yield mathematically processed by the method of variance analysis.

During the three study years the results of the observed characteristics retained their trend among the variants which allowed their presentation on average for the experimental period.

Results and discussion

The herbicide Imazamox applied alone or with the adjuvant Desh

possesses high selectivity to lucerne, birdsfoot trefoil and sainfoin. It belongs to the group of wide-spectrum herbicides with phytotoxic action to the annual mono- and dicotyledonous weeds. Under the trial conditions Capsella bursa pastoris L. and Thlapsi arvense L. showed high susceptibility; they are also the main weeds of the old stands of the studied species. Our observations showed complete killing of the weeds that were at earlier stages of their development (seedlings and rosette) at the moment of treatment. The weeds that were at a more advanced stage remained chlorotic and formed no flower-bearing stems. In view of the circumstance that in these stands a considerable part of the weeds wintered successfully, the timely treatment at the first opportunity in spring was a necessary condition of reaching high herbicidal efficacy.

The herbicidal efficacy (Table 2) with regard to the weed weight in the standard and Imazethapyr reached 96-98% in different crops. The values

for Imazamox at the rate of 20 ml a.i.ha-1 with the adjuvant Desh at the rate

of 1000 ml ha-1, being within the range of 93-97 %, were the closest to these. When comparing this efficacy with that for the application of the herbicide alone it was evident that owing to the adjuvant Desh it was higher by 17 to 19%. The synergistic action of the activating additives was also reported by other authors who explained it by an increase of the retention and absorption of the herbicidal solution by the leaves (Borona et al., 2003; Woznica, 2005).

At the lower dose of the adjuvant of 500 ml ha-1 the herbicidal efficacy


44

increased by 9 to 10% as compared to its application alone. The results showed a unsatisfactory herbicidal effect (71-79%) when applying the herbicide alone (V3), as well as when applying it with the adjuvant Desh at the lower doses (V6).

The removal of the competitive effect of the weeds led in an increase of the participation of the cultivated components in the swards of the perennial legume crops and as a result the dry biomass productivity also increased (Table 3). This increase was 2.4 to 2.8 times in the treated lucerne stands and 1.1 to 1.4 times in birdsfoot trefoil and sainfoin.

The highest yields of dry biomass, close to those of the weeded check and the standard, were harvested from the lucerne, birdsfoot trefoil and sainfoin stands treated with Imazamox + Desh at the rates of 20 + 1000 ml

a.i.ha-1 reaching 4700, 2690 and 6350 kg ha

-1, respectively. The differences

in the absolute values of the dry biomass yields had very good positive significance. Tab. 1. Trial variants

Variant* Rate, ml a.i.ha-1

V1 – Check – zero -

V2 – Imazethapyr 100 a.i.L-1 (Pulsar 100SL)-standard 40

V3 – Imazamox 40 a.i.L-1 (Pulsar 40) 20

V4 – Imazamox 40 a.i.L-1 (Pulsar 40)+Desh (adjuvant) 20+500

V5 – Imazamox 40 a.i.L-1 (Pulsar 40)+Desh 20+1000



V8 – Check – weeded - *The variants of V1 to V8 were laid out in three perennial legume crops: lucerne (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.) and sainfoin (Onobrychis vicifolia Scop.) Tab. 2. Efficacy of Imazamox 40 a.i.L-1 (Pulsar 40) in perennial legume crops

Lucerne (Medicago sativa L.)

Birdsfoot trefoil (Lotus corniculatus L.)

Sainfoin (Onobrychis vicifolia Scop.)

Weeds/m2 Weeds/m2 Weeds/m2 Variant

number weight,g HE*,% number weight,g HE*,% number weight,g HE*,% V1 534 655 - 322 679 - 280 590 - V2 10 15 98 12 28 96 6 12 98 V3 143 161 76 97 175 74 73 125 79 V4 26 94 86 59 115 83 25 67 89 V5 12 31 95 27 49 93 9 19 97 V6 144 169 74 103 199 71 81 141 76 V7 104 101 85 65 129 81 38 78 87

Influence of the adjuvant Desh on the efficacy and selectivity of imazamox 40 a.i. l-1 (Pulsar)

45

HE* - herbicidal efficacy

Tab. 3. Influence of the treatment with Imazamox 40 a.i.L-1 (Pulsar 40) on dry biomass productivity of perennial legume crops

Dry biomass

Lucerne (Medicago sativa L.)

Birdsfoot trefoil (Lotus corniculatus L.)

Sainfoin (Onobrychis vicifolia Scop)

Variant

kg/ha-1 %V1 kg/ha-1 %V1 kg/ha-1 %V1 V1 1680 100 1820 100 4310 100 V2 4810 286 2770 152 6350 147 V3 4210 250 2150 118 5010 116 V4 4450 265 2370 130 5530 128 V5 4700 280 2690 148 6350 147 V6 4150 247 2130 117 4920 114 V7 4330 258 2260 124 5230 121 V8 4920 293 2860 157 6430 149 GD P5% 68,7 140,2 135,1 P1% 95,4 194,7 187,5 P0,1% 132,7 270,7 260,8

Conclusion

The herbicide Imazamox 40 a.i.ha-1 (Pulsar 40) at the dose of 20 ml a.i.ha-1 in combination with the adjuvant Desh at 1000 ml a.i.ha-1 applied in

early growing seasonon of lucerne, birdsfoot trefoil and sainfoin had high

selectivity and herbicidal efficacy reaching 93-97%; Treatment of swards of perennial legume crops improved their

botanical composition and increased dry biomass productivity 1.4 to 2.8 times.

Reference BENKOV, B., I.PRODANOV, (1975): In: Chemical weed control, Zemizdat, Sofia. DIMITROVA, TS., (1987): Influence of weeds and their control on forage yields and sward

botanical composition of pure and mixed birdsfoot trefoil stands, Plant Science, XXIV, 1, 65-68.

DIMITROVA, TS., (1995): Study of the influence of growing method and weed control on the degree of weed infestation and seed yield of sainfoin, Contemporary Plant Protection (Proc. Papers, October 1995), Sofia, 462-466.

DIMITROVA, TS., (2001): Biological study of the herbicide Speed 10SL (Imazethapyr 100g/l) under out-of-vegetation treatment of lucerne (Medicago sativa L.), Proc. Scientific Works of AU – Plovdiv, vol. XLVI, No.2, 205-208.

NIKOLOVA, V., K.KONSTANTINOV, (1989): Study of compensation changes of weed associations in vegetable crops and potatoes – a basis for accurate prognosis and efficient control, Proc. Plant Protection in Aid of Agriculture, Proc. IPP, USWB,


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Sofia, 225-245. STOYKOVA, M., TS.DIMITROVA, (2005): Comparative economic analysis of efficiency

of the plant protection practices used in lucerne forage production, Agricultural Economics and Management, 50, 4, 54-58.

BECKIE, H. I., HEAP,I..M., SMEAA, R.I., HALL, L. M., (2000): Screening for herbicide resistance in weeds, Weed Technology, 14 (2) 428-445.

BORONA, VL., V.ZADOROZHNY,T. POSTOLOVSKAY, (2003): The influence of adjuvant on the efficacy of graminicides in soybeans and nicosulfuron in maize, Herbologija, vol. 4, № 1, 151-155.

DOGAN, M.N., BOZ,O., ALBAY, F., (2002): Influence of some additives on the efficacy of nicosulfuron in maiz and fenoxa-prop-P-ethyl in wheat, Proc. 12 th EWRS Symposium, Wageningen (The Netherlands), 94-95.

HARKER, K., G. CLAYTON, J. O’DONOVAN, R. BLACKSNAW, F. STEVENSON, (2004). Herbicide timing and rate effects on weed management in three herbicide – resistant canola systems. Weed Technology, 18, 4, 1006-1012.

HEAP, I., (2004): International Sulvey of herbicide - resistant weed. http: www weed science. org. Accessed 22 November, 2004.

KIELOCH, R., K. DOMARADZKI (2005): The influence of relative humidity on Anthemis arvensis and Stellaria media control by tribenuron - methyl used alone and with adjuvants. 13 th EWRS Symposium, Bari, Italy, CD – ROM.

KUDSK, P., STREIBIG, I.C., \2002|: Herbicides-a double – edged sword? Proc. 12 th EWRS Symposium, Wageningen (The Netherlands), 94-95.

LEE, I.M., OWEN, M.D., (2000): Comparison of acetolactate synthase enzyme inhibition amond resistant and susceptible Xanthium strumarium biotypes, Weed Science, 48 (3) 286-290.

LESCAR, L., AUDY, (1971): Comptes rendus des journees d’etudes sur les herbicides, t. 4. COLUMA.

MASSINGA, R., K. AL-KHATIB, P. ST. AMAND, J. MILLER (2005): Relative fitness of imazamox resistant common sunflower and prairie sunflower. Weed Science, 53, 2, 166-174.

MATHIASSEN, S., PER KUDSK (2002): The influence of adjuvants on the efficacy and rainfastness of iudosulfuron. 12 th EWRS (European Weed Research Society) Symposium 2002, Wageningen, 206-207.

POZNIAK, C., F. HOLM, R. HUCL (2004): Field performance of imazamox – resistant spring wheat. Canadian Journal of Plant Science, 84, 4, 1205-1211.

STOUGAARD, R., C. MALLORY – SMITH, J. MICKELSON (2004): Downy brome (Bromus tectorum) response to imazamox rate and application timing in herbicide – resistant winter wheat. Weed Technology, 18, 4, 1043-1048.

WOZNICA, Z., (2005): Recent advances in adjuvant formulation thechnology, 13 th EWRS Symposium, Bari – Italy, CD – ROM


HERBICIDE-RESISTANT CROPS - ADVANTAGES AND RISKS

Zvonko Pacanoski

Faculty for Agricultural Sciences and Food, 1000 Skopje, R. Macedonia [email protected]

Abstract

Revealing of genetically modified, herbicide-resistant crops (HRCs) at the end of the 20th century brought many controversies. At one side, HRCs enable the farmers to more effectively use reduced or no-tillage cultural practices, eliminate of troublesome weeds resistant to some herbicides, using nonselective herbicides, usually glyphosate and glufosinate as “environmentally friendly” herbicides, decrease of expenses for crop production, and finely, more economically and effectively manage of weeds. At the other side, there is fear of possibile developing of weed resistant to non-selective herbicides, appearance of volunteer HR crops, invasion of the environment beyond the farm boundary, influence of HRCs to biodiversity, exchange of genetic material between related HRCs and wild progenitors, conventional crops, and weeds. The coming period should clarify the eventual impact of these powerful new tools on weed science, weed management, environment and human health.

Keywords: Genetically modified organisms (GMOs), herbicide-resistant crops

(HRCs), glyphosate, glufosinate, weeds

Introduction

Weed control obtained a new dimension with recent revealing and practical application of plant growth regulators. From that moment chemical industry in collaboration with science have focused on creation of new herbicide active ingredients with large efficacy, selectivity and possibility for use in all crops against almost all weed species. In that period has developed opinion that weed problem would be dissolved forever, without investing efforts in finding and development alternative methods for weed control. However, a long period did not pass when the first problem appeared - resistance of some weeds to some herbicides, on which, until that moment the weedd had been susceptible. The number of resistant weeds to some herbicides continuously have increased. According HRAC and WSSA, about 182 weed species worldwide (109 broad-leaved and 73 grass weeds) developed resistance to large number of different herbicides from all mode of action groups. In the beginning, increasing the herbicides rate was one of

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possible solution for this problem. However, the success was of short duration and partial, but harms were double. Namely, after certain period the resistance appeared again, and first environment damages concerning pollution of the soil, surface and underground water. Some widely used herbicides were out of use and forbidden, but weed problem stay remained. Science and chemical industry were faced with challenge to find alternative ways in combating weeds. Many of them (biological, physical, alellopathy) gave insufficient results, and they are not adequate substitute for herbicides.

Recently, in the solving on this problem, biotechnology with genetic engineering were involved. Scientists are now creating new plants, in order to fight weeds more simpler, cheaper, and at the same time, to stop pollution of environment. All these points of view and principles are taken into consideration in creating of genetic modified organisms (GMOs)

The aim of this review is to give some information about GMOs, particularly HRCs, their advantages, disadvantages and risks for plant biodiversity.

From the moment creating GMOs to the time of their marketing (1995), short period passed, but their planted area year after year have been increasing. According Berca (2004), GMOs are cultivated 12% more in 2002 compared to 1995, 15% more in 2003 compared to 2002, respectively. According to ISAAA, sowings of GM crops rose to 81 million hectares in 2004 recording a 20 percent increase over 2003.

Generally, GM crops are planted in 18 countries, at about 10 million farms. The biggest producers of GMOs (James, 2003) are: USA, Canada, Argentina, Brazil, and China. These countries account to about 98% of all world GMOs production.

Tab. 1. The biggest world producers of GMO in the world (James, 2003)

Country Surface mil. ha % of total cultivated GMO

USA 42,8 63 Argentina 13,9 21 Canada 4,4 6 Brasil 3,0 4 China 2,8 4

Tab. 2. Distribution of GMO on products (James, 2003)

Crops Surface mil. ha % of total

cultivated GMO Soya 41.7 61

Herbicide-resistant crops – advatages and risk

49

Maize 15.5 23 Cotton 7.2 11 Canola 3.6 5

Advantages of herbicides resistant crops

About 71% (more than 40 million hectares) of total cultivated GMOs

in the world are herbicides resistant crops (HRCs). The reason why the biggest percent of GMOs are HRCs lie in the numerous advantages of this new technology in weed control. One of the main benefits is the possibility of controlling a range of broad-leaves and grass weeds with one or two properly timed application of glyphosate (Baldwin, 1999). Conventional herbicide method required applications of two or more different herbicides. In addition, conventional herbicide programme is tightly connected with crop and weed growth stages, also with ecological conditions (climate and soil). Taking into consideration all these factors, possibility for potentional crop injury are high (Johnson et al., 2002). Cultivating transgenic crops enable using nonselective herbicides, usually glyphosate and glufosinate, usually once, but in some cases two applications of these herbicides controlled weeds. At the same time, application period is more flexible than in conventional way; it does not depend of growth stages of crops and weeds, while the possibility for injury crop is minimal (Carpenter and Gianessi, 1999).

Utilization of new method of weed management reduces application of long-term residual herbicides, that are, according to new environmental standards, unacceptable (Shaw et al., 2001). New weed management technology is particularly applicable in the places with weeds dominant resistant to some selective herbicides. In these circumstances, glyphosate and glufosinate are a good solution for this problem, because efficacy of these herbicides is very high. One of these herbicides is capable, alone, to solve the weed problem, even better than standard combination of two or three selective herbicides.

Numerous investigations confirmed excellent results in efficacy of new way of weed control, which is usually more than 95%. Since neither glyphosate nor glufosinate have residual activity after their application, second application, if necessary, is possible for achieving weed-free crops.

The other major advantage of using glyphosate and glufosinate in HRCs is their role in no-till and zero-till agriculture. Minimizing or eliminating soil tillage reduces or prevents soil erosion, humus degradation and destruction of soil structure. However, the weeds soon become main problem in such a system if previous mentioned herbicides are not used.

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In context of this thesis are farmer’s reactions cultivating transgenic maize and soybean resistant to glyphosate and glufosinate under no-till conditions. Their reactions are mainly positive and they confirm that using transgenic crops give bigger opportunities in better weed management system with lower herbicide inputs.

Beside excellent efficacy in weed control, glyphosate is environmentally friendly herbicide. After glyphosate is applied to forests, fields, and other land by spraying, it is strongly adsorbed to soil, remains in the upper soil layers, and has a low propensity for leaching. Glyphosate readily and completely biodegrades in soil. Its average half-life in soil is about 60 days; main product of its degradation is aminomethylphosphoric acid, which is broken down further by soil microorganisms as well. Glyphosate is practically non-toxic for birds, mammals and bees (LD50 for rats is 5600 mg/kg. Oral LD50 for rabbits and goats is more than 10,000 mg/kg)

Similar is the situation for glufosinate, as nonselective contact and nonpersistent herbicide with moderate leaching. Glufosinate is also environmentally friendly and practically non-toxic (oral LD50 above 2000 mg/kg and dermal 4000 mg/kg). It has no residual activities and does not inflict restriction to crop rotation. Half-life is about 40 days.

Tab. 3. Ecotoxicological categories

Toxicity category

Mammalian (acute oral)*

mg/kg

Avian (acute oral)*

mg/kg

Avian (dietary)_

ppm

Aquatic organisms‡

ppm Very highly toxic <10 <10 <50 <0.1 Highly toxic 10-50 10-50 50-500 0.1-1 Moderately toxic 51-500 51-500 501-1000 >1-10 Slightly toxic 501-2000 501-2000 1000-5000 >10-100 Practically non-toxic >2000 >2000 >5000 >100

Except for weed control, glyphosate and glufosinate are efficient

against some plant pathogens. For instance, glufosinate inhibits infection of glufosinate-resistant creeping bentgrass (Agrostis palustris) with several plant pathogens (Liu et al., 1998). Also, HRCs can be especially useful for eradication of parasitic weeds (Joel et al. 1995). According Altman (1993, cited by Duke, 1999), more additional and profound investigations need to be done on secondary effects of these herbicides in order to fully determine their roles in integrated pest management.

Taking into consideration all previous mentioned advantages of new technology, herbicide industry appears to be rapidly transforming from a


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chemically based to biotechnology oriented industry. The largest pesticide producers of the US and Europe have invested heavily in plant biotechnology and seed industry. Every year, since the first experimental releases in 1987, HRCs have accounted for nearly one-third of field tests conducted under USA authority. The biggest part of trials are conducted by companies experts who have created and applied new technologies. Successful creation of new HRCs will be economical method of expanding the market for products for which companies have already have sophisticated equipment and highly specialized staff.

Possible risks and concern of GMOs

As every new technology, also GMOs, beside positive, may have

some potentially negative aspects, which are, fortunately, still in the domain of speculation. Controversies surrounding GMOs commonly focus on human and environmental safety, labelling and consumer choice, intellectual property rights, ethics, food security, poverty reduction and environment conservation. Some of them are real and the experts are aware for that. They take every measure to eliminate them on time. There is not any reason for concern. The following text will elaborate some of the potential risks and negative implication from HRC technology.

One of the real risk in cultivation of HRCs is possibility for development of weed resistant mechanism to non-selective herbicides. Namely, application of unilateral strategy in weed control management and multiple glyphosate and gluphosinate application presents serious threat in the process for appearing of resistant weeds (Derksen et al., 1999). Weed resistance to glyphosate and gluphosinate, according some authors (Bradshow et al., 1997; Waters, 1991) is less probable, and will be rarer evolved to glyphosate and gluphosinate than to many other herbicides. The reason for this, according to these authors, is slow development of functional genes of resistance and the rich biodiversity in agroecosystem where these herbicides are applied. Nevertheless, glyphosate-resistant weeds have appeared, first in rigid ryegrass (Lolium rigidum Gaudin). in Australia (Powels et al., 1998; Pratley et al., 1999), then goosegrass (Eleusine indica L. Gaertn) in Malaysia, and subsequently, hairy fleabane (Conyza banariensis LO. Cronq.) and horseweed (Conyza canadensis L. Cronq.), in the USA (Heap, 2001). Resistance to glyphosate in Australian ecosystem is result of long-term application of this herbicide in no-till system. No-till system has poor diversity than conventional systems. Weed resistance to glyphosate in the USA is recorded in HR soybean because of continuous use in so-called minimal diversity system (Powels, 2003). It is clear that weed resistance to glyphosate in previous mentioned agroecosystems is due to poor diversity

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and unilateral weed control management. More scientists who study this weed-resistant phenomenon, agree about possibility for escalation of this problem and they emphasize importance for designing appropriate system to prevent development of weed-resistance in HRC system. Increased diversity i.e., a wider range of rotational crops, diversity of herbicides used (herbicides with different mode of action, for example sulfentrazol + glyphosate in soybean) (Krausz et al., 2003), better cropping practices leading to more competitive crops, and use of nonherbicide weed control, can reduce the dependence on glyphosate and reduce the likelihood of resistance developing.

Other risk for this system are “volunteer HR crops”. Long-term use of HRCs, particularly in crop rotation system only with HRCs, can be a serious problem. Namely, the volunteer plants of previous HR crop in the next HR crop can be problem, if the next HR crop is resistant to the same herbicide like the previous one. To avoid this real risk, it should be applied a preventive strategy such as presowing/preplanting soil cultivation and application of alternative soil herbicides. The herbicides choice should be done very careful, because of possibility of multiple and crossing herbicide resistance. The best way to prevent this undesirable appearance is application of herbicide with different mode of action than glyphosate and glufosinate. Appearance of volunteer HR plants is concerned particularly in harvest of transgenic rice and soybean, when some seeds can shed on the soil during this operation.

Introduction of new technology impose the question for possible influence of HRCs to biodiversity. It can not give precise answer on this question, although numerous investigations with HRCs are made all over the world. Maybe we can answer this question indirectly, toward conventional crop production and its influence to biodiversity.

The most important crop grown in Brazil is soybean, with approximately 13 million ha planted. The most important weeds associated with the crop belong to families Poaceae, Amaranthaceae, Cyperaceae, Euphorbiaceae and Asteraceae (Foloni and Christoffoleti, 1999) (cit. by Riches and Valverde, 2002). Agriculture intensification, adoption of non-tillage systems, and overreliance on herbicides has resulted in the increased occurrence of hard to kill broad-leaf weeds, including those in the genera Cammelina, Euphorbia, Ipomoea, Borrerlia and Tridax (Merotto et al., 1999). Additionally, wild poinsettia (Euphorbia heterophylla L.) and hairy beggarticks (Bidens pilosa L.) have evolved resistance to ALS inhibitors (Ponchio et al., 1997; Theisen et al., 1997; Vidal et al. 1997). In Argentina, pigweed (Amaranthus quitensis H.B.K.) evolved resistance to imazethapyr and chlorimuron in soybean (Christoffoleti et al.,1997, cited by Riches and Valverde, 2002). Non-tillage systems and unilateral ALS-herbicide application changed biodiversity in the soybean.


53

According to the fact that weeds are an important component of agrobiodiversity, shifts in the composition of weed flora provoke change of biodiversity (Spahillari et al.,1999). The impact of HRCs to biodiversity will be the same. According to Forcella (1999), it could be anticipated that most HRCs are associated with nonresidual herbicides and the promotion of zero-tillage, the seed bank density of weeds with protracted emergence periods or of those emerging late in the growing season is more likely to increase as compared with that of other species more easily controlled.

Changes in the type and frequency of herbicide application in HRCs will provoke gradual removal on perennial and colonization of annual weeds (Sweet et al., 1999). For biodiversity conservation and avoiding undesirable effects, choice of complex measures of weed control (integral weed management) is needed, particularly regular and timely soil cultivation, crop rotation and application of herbicides with different mode of action.

One of the potential questions is: can HRCs become invasive beyond the field boundary? Numerous experts agree that HRCs can not survive out of the agroecosystem’s boundary. This thesis is corroborated with the fact that in the process in their selection with application of molecular biotechnology, and then in the process of domestication, HRCs became completely depended on human activities. For example, transgenic varieties of soybean and maize which are cultivated in South America, according to Colwell (1994), are weak competitors to plants species out of the arable land.

However, the possibility for exchange of genetic material between related HRCs and wild ancestors, conventional crops and weeds, concern scientists most. This phenomenon is very possible in the centers of their origin. Geographic distance and pollination system are key factors in existing of probability for genes exchange. Soybean, the first and the most cultivated worldwide HRC, is exotic plant, whose wild progenitors originated from China, Russia, Japan, and Korea (Palmer et al., 1996). That means, if HR soybean is cultivated out of its origin centres there is not threat for gene exchange and, in the same time, for plant biodiversity.

Existing and real risk is possibility of exchange of genetic material between transgenic and conventional crops. Particularly this problem is stressed for farms certified for so-called organic production. In order to avoid pollen transmission from transgenics crops to crops for organic, and also, for conventional production, space isolation is necessary. But, still there does not exist precise regulative, which will define minimum distance between trangenics and other crops. The most serious threat for new technology is possibility for gene exchange between related HRCs and weeds. Many different sources have been consulted and analyzed in order to estimate risk of appearance of hybrids between HRCs and weeds. According to scientific investigations of

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Keeler et al. (1996) and Arriola (2000) based on numerous research activities in Europe and North America, it is clear that HR crops and related weedy plants can exchange genes through pollen transfer. The identification of spontaneous hybrid forms in a number of crop-weed complexes is well established, including between Sorghum halepense (L.) Pers. and Sorghum vulgare Pers., and between wild and cultivated forms of Helianthus annus L.and Oriza sativa L. (Arias and Reisberg, 1994; Arriola and Ellstrand, 1996). According to Dale (1994), possibility for gene exchange between HRCs and weed population depends of three factors:

i) sexual compatibility between crop and weed ii) possibility of spontaneous exchange of genetic material

between crop and weed (spontaneous hybridization) iii) the manner in which new characteristic in the crop-weed

hybrid will behave under environmental conditions Formation of hybrids between HRCs and weeds will provoke

difficulties in weed control, similar to those with herbicides resistant weeds in conventional crop production. The sexual transfer of genes from crops to weeds, as it was mentioned before, is probably the biggest risk for the environment and can limit the cultivation of transgenic species. It is case of weeds related to transgenic canola which transfers her pollen towards wild species of Brassica, Sinapis etc. To avoid this phenomenon, today a specific management is practiced, which involve: i) maternal inheritance ii) male sterility iii) seed sterility iv) cleistogamy v) apomixis vi) incompatible genomes If maternal inheritances are presented, the interest gene is expressed

only in chloroplasts and can not be dispersed through pollen to non-transgenic plants. Male sterility (sterility of pollen) is very important to eliminate the crossings in the environment (outcrossing). Therefore, transgenic plants should be created by getting seeds where the interest gene should be dominated in the mother plants, and pollination should be done with a non-transgenic line.

At cleistogamic plants pollination is made inside the flowers before these open. In this way the external crossing can be avoided (the case of Triticum durum).

Apomixis is an asexual type of reproduction in which the plant embryos grow from egg cells without being fertilized by pollen—the male


55

part of the plant. The result is production of seed which inherited only maternal genes, and the plants are identical with maternal plant.

Conclusions

Taking into consideration all advantages, disadvantages and risks

which are connected with the new technology, particularly with HRCs, undoubtly one question is posed: how and to what extent is possible use HRCs without causing undesirable effects? In order to be controlled, the new technology should be regulated by low. That means preparation and verification of international GMOs regulations and norms, possibilities of the pesticide-biotechnology industry to protect and recoup their investments

Several countries have already established legislation on the release of HRCs which are product of the new technology. The EU states in the recently revised Directive 2001/18/EEC states that GMOs have to undergo a scientific assessment of risks to human health and environment. The Directive presents a framework for the risk assessment, which appears to be derived from the framework put forward by the joint consultation on food safety brought up by the World Health Organization (WHO) and Food and Agriculture Organization (FAO).

It is clear, that HRCs are (or soon will be) strongly impacting weed management choice. Their mass use will decrease the cost of effective weed management in the short or medium term. Their use will speed up adoption of reduced and no-tillage agriculture, greatly reducing the environmental damage by farming by reducing soil erosion (wind and water) and by reducing the use of herbicides likely to be found in surface and ground water. Herbicides resistance and new weed species that arise as a result of this technology will be dealt with traditional methods, such as rotating and mixing herbicides and rotating crops.

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ARRIOLA, P.E., ELLSTRAND, N.C. (1996): Crop-to-weed gene flow in the genus Sorghum (Poaceae): spontaneus interspecific hybridisation between johnsongrass, Sorghum halepense, and crop sorghum, S. bicolor, American Journal of Botany, 83, 1, 153-160

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PRODUCTION OF ALLERGENIC POLLEN BY RAGWEED (AMBROSIA

ARTEMISIIFOLIA L.) IS INCREASED IN CO2-ENRICHED ATMOSPHERES

Taib Šarić1, Ivica ðalović2

1Faculty of Agriculture, Sarajevo, Bosnia&Herzegovina, e–mail: [email protected]

2Faculty of Agriculture, Čačak, Serbia&Montenegro

Abstract

Ragweed (Ambrosia artemisiifola L.) is tipically a pioneer plant, which invades recently disturbed soils. It belongs to the group of the annual plants that emit pollen during late summer and early fall near the end of the growing season. This pollen is produced in such large quantities that is a key contributor to ex-Yugoslavia hay–fever problems near the end of summer.

Anemophilous pollen grains are airborne and meteorological factors have great impact on their dispersal. Precipitation, wind speed, temperature and air moisture are often cited as influencing airborne pollen concentrations (Emberin et al., 1996). Numerous studies have already dealt with these aspects. Recently, Bartkova et al. (2003) showed that temperature has a marked impact on ragweed pollen production in Bratislava, Slovakia. Relative humidity is an important factor as well but not quite as determining. In the same direction, Barnes et al. (2001) noticed that usual weather conditions, temperature and relative humidity have onl little influence on the day–to–day variation of ragweed pollen counts. However, unstable atmospheric conditions such as the crossing of a cold front has the greatest impact of all the weather–related events on airborne ragweed pollen counts. According to the authors, only heavy rainfall has a distinct impact on pollen concentrations. Peak pollen production has been described to occur shortly after sunrise and may be related to photo cycle periods or cooler morning temperatures and lower humidity. Different statistically based types of models trend to predict pollen concentrations from meteorological conditions as reported by Laiidi et al. (2003). Bringfelt (1982) subsequently published some correlation studies dealing with pollen concentrations and weather parameters for forecasting purposes. One of his main conclusions is that daily temperature values from early spring have a major influence on the timing of the beginning of the pollen season and subsequently on its day–to–day variation. Keywords: ragweed, aeroallergens, allergy, pollen, CO2, climate change

T. Šarić and I. ðalović

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Introduction

Recent studies have shown a link between warming trends within the past 50 years and the phenology and abundance of allergenic pollen released by a number of European tree species (Jaeger et al., 1996; Emberlin et al., 1997). However, only limited data are currently available to evaluate the direct effects of rising atmospheric CO2 concentrations on pollen production by allergenic plants and its potential impact on public health (Ziska and Caulfield, 2000).

Human allergic responses to the pollen of certain plant species (hay fever and allergenic rhinitis) is a serious environmental health issue (National Institute of Health, 1993). Aeroallergens, including pollen, also play a role in the exacerbation of asthma (D'Amato et al., 1994). The prevalence of both hay fever and asthma has increased significantly in recent decades (Wuthrich, 1991; Arrighi, 1995). Little research has been devoted to understanding how various components of global environmental change influence allergenic pollen production and, thus, the potential for pollen-related disease.

An increase in the concentration of atmospheric CO2 is one of the most certain predictions of climate change models. CO2 concentration has increased by 29% since preindustrial times, and is expected to double again sometime between 2050 and 2100 (Houghton, 1996).

Plants grown in CO2-enriched atmospheres generally grow faster and are larger at maturity, although the magnitudes of growth and physiological enhancements vary considerably with environmental conditions and species identity (Bazzaz, 1990; Curtis and Wang, 1998). In one recent study, Ziska and Caulfield (2000) found that exposing ragweed plants to the higher CO2 concentrations predicted in the year 2100 doubled the quantity of pollen produced.

Ragweed is a plant common to roadsides and disturbed habitats throughout most of the United States and Canada (Basset and Crompton, 1975). It has male and female flowers born on distinct axillary branches, allowing for independent control of allocation to sexes (Payne, 1963). Throughout its distribution, ragweed pollen is one of the most abundant aeroallergens in late summer and fall, and it is one of the primary causes of seasonal pollen allergy in North America (Lewis et al., 1983).

Consequently, ragweed pollen and specific allergens extracted from it have been used in many clinical studies, and the biochemistry and genetics of ragweed allergens and their impacts on the human immune systems are well understood (Griffith et al., 1991; Naclerio et al., 1997).

This study investigates the direct impact of rising CO2 concentrations on pollen production of ragweed. The results can be used to more accurately

Production of allergenic pollen by ragweed (Ambrosia artemisiifolia L.) is increased in ...

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evaluate the future risks of hay fever and respiratory disease exacerbated by allergenic pollen, and to develop strategies to mitigate them.

Pollen

Most pollen grains are smaller than 80 microns which is about the width of a human hair. Some pollens cause allergic reactions in some people. Pollen allergies are specific to the individual and the pollen type. Pollen grains that are wind-dispersed cause most of the allergy problems because these are the pollens that make their way into our nasal passages and eyes. Pollens from some plants, such as roses and tulips, are too big to be transported by the air alone. They depend on insects and birds to carry the pollen from plant to plant.

Most pollens are spherical in shape. Ragweed pollens, which bothers many people, appear to have spikes or other similar features.

While grass pollen is most prominent in May and continues into September, most weed pollen quantities increase throughout May and into June, ragweed pollen is very significant from late August through mid-September. The first hard frost of autumn typically brings our pollen season to a close in October. Pollen seasons can last for several months.

On average, grasses are the most potent pollen grain on human allergies. To put this in perspective, here is an example. If the air had a pollen density of 90 grains/m3 for trees, it would take a density of only 20 grains/m3 for grasses to cause the same level of symptoms associated with allergies. It would take 50 grains/m3 for weeds. On a grain for grain basis, grass pollen has a higher allergic potential than either tree or weed pollen. Because of these differences in allergic potential, it takes a higher density of weed or tree pollen to constitute a "high" pollen rating than it takes for grass pollen.

Some studies have examined trends in pollen amount over the latter decades of the 1900s and found increases to be associated with local rises in temperature (Corden and Millington, 2001; Spieksma et al., 1995). Changes in climate appear to have altered the temporal and spatial distribution of pollen. For example, some studies have found that trends toward earlier pollen seasons are associated with local warming over the latter decades of the 1900s (Emberlin et al., 2003; Fitter and Fitter 2002), and recent reports have concluded that the duration of the pollen season is extended in some species (Huynen and Menne 2003). Finally, several studies have examined other attributes of allergenic plants, which have also been responsive to CO2 concentration and/or temperature increases (e.g. Menzel 2000; Wulff and Alexander, 1985). These latter studies provide indirect evidence of impacts of climate change on pollen aeroallergens.


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Impacts of climate change on aeroallergens: past and future

A number of studies have revealed potential impacts of climate change on aeroallergens that may have enormous clinical and public health significance.

Human activities have resulted in increases in the concentrations of atmospheric greenhouse gases and changes in global climate. Before the Industrial Era (circa 1750) atmospheric carbon dioxide (CO2) concentration was 280±10 ppm for several thousand years (Prentice et al., 2001). It has risen since then to 373 ppm (Keeling and Whorf, 2004).

It is estimated that global average surface temperature changed increased by 0.60C since the late 19th century. Projected CO2 concentration by 2100 ranged from 541 to 970 ppm (approximately 1.9 and 3.5 times the pre-industrial concentration). Global average surface temperature is projected to rise over the period 1990–2100 under all scenarios, ranging from 1.40C to 5.80C (Cubasch et al., 2001).

Climate change is likely to have impacts on hayfever (allergic rhinitis) and asthma via its impacts on pollens and other aeroallergens.

Atmospheric variables that may have impacts on these allergens include CO2 concentration, temperature, rainfall, humidity, and wind speed and direction. With allergic diseases already being a significant public health issue in many countries, the potential for any adverse impact resulting from climate change is of serious concern.

Impacts of climate change on aeroallergens

Pollen amount

A number of studies have found increases in pollen associated with increases in CO2 concentration and/or temperature. Ziska and Caulfield (2000) found pollen production of common ragweed increased significantly both from pre-industrial to current and current to the future CO2 concentration. Similarly, Wayne et al. (2002) found a significant increase in ragweed pollen production under an approximate doubling of the atmospheric CO2 concentration, although the increase was smaller than that found previously by Ziska and Caulfield (2000), who had examined a smaller increase in CO2 concentration from current to future.

The impact of climate change on pollen production of common ragweed (Ambrosia artemisiifolia) has been assessed by Ziska et al. (2003), who used an existing CO2/temperature gradient between rural and urban areas. The higher CO2 concentration and air temperature of the urban area resulted in ragweed that produced significantly greater pollen than that at the rural areas. Ragweed also flowered earlier in urban than in the rural areas.


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Significantly stronger allergenicity was found in the pollen from plants grown at the higher temperature.

Plant and pollen distribution

The potential for changes in the distribution of allergen producing species has been recognized since the early days of climate change and human health work (Last and Guidotti, 1991). It has been suggested that areas of perennial ragweeds are likely to extend, and northern colonies of annual ragweed, such as that in the UK, will probably become more persistent (Emberlin, 1994).

There is some evidence that vegetational response to abrupt climate change, such as that expected over the coming decades, may be rapid (Peteet, 2000). Weber and Mother (2002) recently suggested that one of the implications of increased pollen production associated with increased CO2 concentration could be more efficient wind pollination and, ultimately, greater propagation of the plant species.

Research challenges

The research done to date is of concern for at least two reasons. First,

it suggests that the future aeroallergen characteristics of our environment may change considerably as a result of climate change, with the potential for more pollen (and mould spores), more allergenic pollen, an earlier start to the pollen (and mould spore) season, and changes in pollen distribution. Second, it demonstrates climate change has probably already had impacts on aeroallergens. However, further work is required. Study of the impacts of climate change on aeroallergens and related diseases presents many challenges. Some of these challenges, along with suggestions for further work, are outlined in this section.

Land-use changes will be a significant factor in determining future aeroallergen, particularly pollen characteristics. For example, Emberlin (1994) has suggested that decreases in grassland and cereals in Europe would lead to decreases in grass pollen, and that the projected increase in oil crops such as oil seed rape (Brassica species) may lead to a greater aeroallergen load.

Although further work is required in this area, with the evidence to date, it would seem prudent to consider alternative adaptive strategies. One adaptive strategy would be tighter management of a number of the allergenic plant species discussed in this article. For example, government authorities could consider more carefully which plant species are used in populated areas. It is important that public health authorities and allergy practitioners be


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aware of these changes in the environment, and that research scientists embrace the challenges that face further work in this area.

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GENETICALLY MODIFIED HERBICIDE–TOLERANT CROPS

– STATE AND PERSPECTIVES

Goran Malidža1, Vaskrsija Janjić2, Ivica ðalović3

1Institute of Field and Vegetable Crops – Novi Sad, Serbia and Montenegro

2Institute of Agricultural Research “Serbia” Centre for Pesticides and Environment Protection – Zemun, Serbia and Montenegro

3Faculty of Agronomy – Čačak, Serbia and Montenegro

Abstract

Development and production of genetically modified crops is the hallmark of the end of last and beginning of new century. The most remarkable commercial success regarding genetically modified crops has been achieved with herbicide – tolerant crops as HTCs offer the potential for many benefits: simpler weed control, more effective management of problematic and resistant weeds, control of parasitic weeds, use of minimum additional tool in integrated weed management, avoidance of yieldtillage, loss caused by current herbicides, etc. Potential risks associated with HTCs include: gene flow, herbicide resistant volunteers, selection of weed flora in favour of species less susceptible to herbicides, potential development of herbicide-resistant weeds, grower's increased dependency on herbicides, reduced application of integrated weed management, losing of traditional skills of weed possible decrease in biodiversity in fields, etc.management, Key words: genetically modified plants, herbicides, tolerance, weeds, resistance, gene flow, integrated weed control.

Introduction

A significant increase in crop production over the recent decades has resulted from growing highly improved cultivars, i.e. their grown hybrids as well as from modern agrotechnical practices.

The latest achievements in molecular genetics, biochemistry and physiology largely contributed to breeding crops of improved qualites, of which the tolerance of herbicides seems the most intriguing. Therefore, the first generation of the genetically modified crops relate to crop inputs or agronomical properties. Genetically modified herbicide–tolerant crops have aroused an interest of numerous stakeholders, unanimously sharing an opinion that farmers, herbicide and plant seed producers benefit from such crops most, with end–consumers benefiting none (McHugen., 2000; James, 2001).

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Over breeding the herbicide–tolerant crops, the methods of recombinant DNA (genetic engineering) may be used to obtain genetically modified, transgenic crops. Biotechnological boom also allowed new organisms to be bred, their isolation mode to come into being as well as some of the DNA fragments to be transeferred, and prokaryotic and eukaryotic genes to be combined, too. Therefore, an ever-lasting dream of geneticists to combine various pedigree genes when breeding organisms with either modified or by introducing entirely new traits or entirely new organisms came into being. (Bekavac et al., 2004).

So far, the combat against weeds has been based on the indigenously herbicide-tolerant crops. However, so applied herbicides over several decades so far have led to numerous problems requiring new approaches to be made. The development of molecular genetics paved the way for genetic transforming of the individual plant species as well as for expanding genetic variability and breeding the herbicide– and other toxic compounds–tolerant crop genotypes. So handled, the genes have encouraged an entirely new herbicide application technology. The concept of genetic transformation or genetic engineering embraces all the DNA processes to be transferred from one organism to another as well as their expression in the host plant. Genetic transformation is considered to be the procedure allowing genes to be transformed between the species irrespective of their being cognate and their number of chromosomes (Hull et al., 2000).

As a technique of foreign DNA transfer to the plant cell, genetic transformation requires the following:

• identifying the gene to be transferred; • isolating and cloning the gene; • introducing the gene into the host genome; • replicating genetic material; • expressing genetic material; • transferring the cell morphogenetic ability, and • introducing structural genes so as to be inherited through generative

reproduction with safety. Methodologically, genetic transformation may be attained by directly

introduced structural genes into the host crop genome or through vectors. The vectors appearing over the gene transfer may be Agrobacterium plasmides, DNA of the crop viruses, DNA of the plant organisms, DNA of pollen as well as that of pollen tube. When breeding herbicide-tolerant crops, the methods of DNA recombinants (genetic engineering) may be attempted, with virtually genetically modified i.e. transgenic crops. In addition, crop tolerance towards herbicides may be exerted using somaclonal variabilities, mutations and commonly used modes in plant breeding (Dyer, 1996., cit. By Malidza et al., 2005).

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Over herbicide–resistant crop growing, the three principles have been taken into account, as follows:

• introducing the genes responsible for hyper-reproduction of the enzyme affected by herbicide;

• altering susceptibility of the crucial locus exposed to herbicide impact and;

• introducing the gene responsible for detoxifying herbicides existing in the crops.

The largest number of herbicide – resistant crops could be got altering the main locus exposed to a herbicide, using induced mutations in crops and microorganisms and introducing microorganism genes to synthesize enzymes responsible for detoxifying herbicides.

An increasing growth of transgenic herbicide–resistant crops has largely contributed to weed control in recent years, with an array of merits favouring producers rather than conventional modes do.

Current issues relating to this field, the significance of the genetically modified herbicide–resistant crops, their most important traits, a detailed account on the relevant accomplishments made worldwide so far as well as possible undesirable effects of the technology considered will be discussed in the paper. Genetically modified and herbicide–tolerant crops as a global challenge

Herbicide–tolerant crops do not seem to be a new phenomenon, their

acceptable level resistance being a fundamental precondition of using herbicides with safety. In addition, a new herbicide is approached by testing its selectivity compared to that in the leading grown plant species. However, due to other requirements to be met (toxicological, ecotoxicological, impact–range, prices etc.) developing new herbicides has been visibly slackened and become rather costly in recent years. Moreover, grown crops have had their tolerance altered due to a booming biotechnology, with tremendously increasing number of herbicide producers making a huge profit. With herbicide – tolerant crops, lower losses in yield, lower pesticide and production costs are expected, too. Booming growth of the genetically modified herbicide – tolerant and insect-resistant crops has upgraded the conventional crop management since the last decade of the last and the first one of current century, their canopy highly expanding (Tab.1).

Tab. 1. Global area of transgenic crops from 1996 to 2003 (James, 2003) Year 1996 1997 1998 1999 2000 2001 2002 2003 Million hectares

1.7 11.0 27.8 39.9 44.2 52.6 58.7 67.7

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As can be seen from Table 1., the total areas under the genetically

modified crops increased by 40 times more from 1996–2003 than those in previous years. (James, 2003). Thus, in 2003, 73% accounted for total areas under transgenic crops, of which soybean, canola, maize and cotton did most (Tab.2). Table 2. Global area of transgenic herbicide-tolerant crops from 1999 to 2003

(James, 1999, 2000, 2001, 2002, 2003) Million hectares

Crop 1999 2000 2001 2002 2003

Herbicide tolerant soybean 21,6 25,8 33,3 36,5 41,4 Herbicide–tolerant canola 3,5 2,8 2,7 3 3,6 Herbicide–tolerant maize 1,5 2,1 2,1 2,5 3,2 Bt /Herbicide–tolerant maize 2,1 1,4 1,8 2,2 3,2 Herbicide–tolerant cotton 1,6 2,1 2,5 2,2 1,5 Bt /Herbicide–tolerant cotton 0,8 1,7 2,4 2,2 2,6

*Bt –insect resistance

From the short – term point of view, not believing in no risks of transgenic crops, the world public seem suspicious and reluctant to put them into practice. For example, the North and South America countries rank best by genetically modified produces, the EU countries still lingering about whether or not to back up such produces. Nonetheless, in Europe, such crops have been estimated to be notably advantageous. Thus, Phipps and Park (2002) estimated that in case of growing genetically modified maize, soybean, canola and cotton resistant to insects, the annual pesticide consumption in the European Union countries would be reduced by 4.4 million kg, with areas to be treated expected to be reduced by 7.5 million hectares, which would save roughly 20.5 million litres of petroleum and reduce carbon – dioxide emission in the atmosphere roughly by 73000 tonnes.

Breeding modes for herbicide–tolerant genotypes

Different biotechnological modes applied to a larger number of crops gave rise to a notably higher crop resistance to herbicides (Tab.3). As the most reliable way in breeding herbicide–tolerant genotypes is reckoned selecting from the existing germplasm. A differing tolerance level to the herbicides was revealed in wheat (Snape et al., 1991) soybean (Fedtke, 1991) and some of the oriental grasses (Catanzaro, et al., 1993). As regards the resistance to herbicides, genetic variability may be attempted, recurrent


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selection intensified along with conventional crossing modes to obtain new cultivars, i.e. hybrids. However, this approach has not been widely accepted by breeders, primarily due to too poor crop genetic variability to withstand herbicides.

Tab. 3. Methods of obtaining plants resistant to herbicides (modified according to Duke, 1996)

Plant species Herbicides Methods Maize Glufosinate

Imidazolinone Ciklosydim

PB C C

Wheat Glufosynate PB Soybean Glyphosat

Sulphonilurea AT

Sugar beat Glufosinate Sulphonilurea

AT AT

Barley Glufosinate PB Tobacco Glufosinate

Glyfosate Sulphonilurea 2,4–D

AT AT AT AT

Legend AT–Transfer og agenes by Agrobacterium tumefaciens PB–Genetic Gun C–Tissue culture S–Plant or seed selection

As a usual method for obtaining herbicide–tolerant crops is assumed

using mutagenous chemicals and X–rays used so far for seed treatment and mutation inducement, thereby helping separate soybean genotypes resistant to sulphonilurea herbicides. Tissue culture is highly significant to the herbicide–resistant genotype breeding. In this sense, growing plant cells in its tissue culture may exert a range of changes in its genetic composition, including those in gene distribution, fertility level as well as those in chromosome arrangement. Such a process, called self-cloning variability has become an important source of variability, which might have been effectively used in breeding (Scoweroft and Larkin, 1988). Despite a somewhat success made in this view at first, a larger number of mutants manifested a range of undesirable effects due to their low ability in this view. In this sense, an example of tobacco cell culture selection on glyphosate resistance is often mentioned. However stable regenerant resistance to glyphosate may be, the crops regenerized could not be used due to partial sterility and undesirable agro–economical properties (Dyer et al. 1988). On the other hand, an

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example in favour of the mode considered may be exposing maize embriogene callus culture to Imidazolinon, with some of its resistant portions being isolated from maize culture (Anderson and Georgheson, 1989). Additionally, several herbicide–resistant lines possessing one of the two partially separated dominant alleles responsible for differing resistance level were regenerized (Newhouse et al. 1991). The mode of recurrent crossings helped breed the lines with preferable agronomical traits, resulting in 14 hybrids resistant to Imidazolinon (Duke, 1996).

Also, as a mode of breeding herbicide–tolerant crops, hybridization favours those plant species, which may be crossed with weed species or wild allies possessing genes resistant to a particular herbicide. Crossing the weed species Brassica campestris resistant to atrazin with several grown species from the family Brassica has launched a few commercially significant genotypes resistant to atrazin, too (Beverski et al., 1980). Despite their yield being reduced by roughly 20% due to undesirable chloroplast mutation, such genotypes have been observed to inhabit extremely weeded areas where the conventionally grown varieties would not be yielding economically enough.

Direct gene transfer claims an absolutely new approach to herbicide – resistant crop breeding. Numerous genotypes have been obtained from the directly introduced desirable foreign genes into the host plant genome. DNA hybridization (Southern blotting) (Sambrook et al., 1987), using DNA polymerase chain reaction (PCR) (Mullis and Faloona, 1987) and enzymatic activity analysis are generally accepted methods for checking whether or not foreign genes have been built in in the host cell gene. Theoretically, the protoplasts and cells inherent to any plant species may be transformed, but the problem of how to regenerate transformants from the callus obtained from plant culture is being inevitably encountered. The modes of direct DNA transfer may be split up into four groups, as follows:

• genetic transformation through Agrobacterium tumefaciens; • “Gene gun”; • stimulating endocytosis chemically; • electroporation, and • microinjection.

Genetic transformation through Agrobacterium tumefaciens The bacteria inherent to the family Agrobacterium are gram negative

soil bacillary microorganisms. Agrobacterium is closely related with representatives of Rhizobium family responsible for nitrogen fixing in the root nodular bacteria intrinsic to Agrobacterium tumefaciens, whereas Agrobacterium rhizogenes may bring about an uncontrollable adventitious root growth (Janjic, 1996).


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DNA transferred from a large bacterium Ti plasmide, subsequently infecting the plant cell, is presumed a key bacterial activity. The DNA portion being transferred contains a gene responsible for phytohormone formation causing tumor tissue. The portion considered is mainly transferred safely to the host plant genome, so that transgenic plant breeding rests on such an intrinsically more natural transfer system. The gene responsible for tumor formation is replaced with a desirable gene and its corresponding vector formed. Gene transfer through Ti cloned carry–overs Agrobacterium tumefaciens is mostly used for breeding transgenic plants such as tobacco, petunia and a range of agronomically significant dicotiledons (Lindsey, 1992). However, the gravest and economically significant drawback of Agrobacterium system is that it cannot help transform monocolitedon plants from the family Poaceae. Its numerous species include the most dangerous and resistant weeds (such as Agropyrum repens (L.), Beauv., Sorghum halepense (L.) Pers. and the like). The efficacy of gene management through Agrobacterium is also undeveloped in certain economically significant dicotiledonous plants such as fruit species, eg. peach and sweet cherry. Indeed, their tissues do not tolerate an infection caused by Agrobacterium or are likely to be oversensitive to the bacterial toxins, thereby discouraging effective genetic transformation.

Gene gun Gene gun helps introduce sped up tungsten or gold particles 1 – 4 µm

by size covered with DNA. Pollen seeds, cell suspension, callus tissues, endosperm, leaf, scion vegetation cones and the like may be the object of transformation. This mode has proven the most efficient for obtaining fertile, transgenic crops of maize, with a somewhat success made in the experiments with soybean, beans, rice etc. (Cao et al., 1992). Of some of the genetic gun designs, the commercially most often used one is Kikker's (1993) gun. Although this method ensures no stable integration of the DNA introduced into the plant genome, it has helped transform maize with success.

Chemical stimulation of endocytosis Protoplast may be transformed by directly stimulated endocytosis.

Under particular conditions (high pH, high content of Ca2+), polyehylene glycol (PEG) and polyvinyl alcohol are likely to reliably exert genetic transformation frequency from 1 – 5 x 10-6. Even a higher degree of genetic transformation via endocytosis could be attained in cauliflower amounting to 7.6 x 10-4 (Tanaka et al., 1984). Methodologically, however complex endocytosis seems to be for implementing genetic transformation, it has proven a mere routine with rice, being attempted in a larger number of the laboratories and varieties (Shimamoto et al., 1989).

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Electroporation Electroporation implies a procedure of exposing cell to electric field

with temporary pores taking place on the plasmalemma through which macromolecules such as DNA enter the cell.

Microinjection Microinjection is referred to as a macromolecule (DNA, RNA, protein,

virus or organelle) being directly pushed into the plant cell. Carry–overs of genetic transformation are directly introduced into the cytoplasm or nucleus intrinsic to the cells being immobilized on a solid medium using glass pipette tip 0.5–0.1 µm by size.

This method enables introducing macromolecules and chromosomes with high precision, with the amount of built – in genetic material controlled with high accuracy, too. The cell wall is not necessary to remove, being useful to the species with an undeveloped regenerating system from protoplast.

The most economically significant genetically modified herbicide– tolerant crops

Theoretically, crops tolerant to all the herbicides may be bred, but only

the economically important plant species and herbicides with more suitable properties (glyphosate, glufosynate ammonium, sulfonylurea, imidazolinon cyclohexandion, bromoxinit and the like) deserve mention. To consider significance of hazards due to such a technology, every single case, i.e. a grown crop and herbicide itself, to which the crop may exhibit resistance, should be analyzed.

Glyphosate–tolerant crops The first commercialised glyphosate–tolerant crops were obtained

introducing the gene for modified enzyme 5–enolpiruvil–shicimat–3–phosphate synthetase (EPSPS) imparting the biosynthesis of aromatic amino acids and being the key locus exposed to this herbicide. The gene for EPSPS, of lower propensity to glyphosate was isolated from Agrobacterium sp., strain CP4, enabling tolerance of the majority of the economically significant plant species (Wells, 1995). The principle of glyphosate detoxification was brought to bear introducing it into the plant gene from the bacterium Achromobacter sp., strain LBAA in order to synthesize an enzyme for glyphosate oxidoreductase (GOX). This enzyme catalyzes the fissure of C – N bonds existing in glyphosate up to the metabolites with no herbicide activity felt (Wells, 1995; Padgette et al., 1996). Taken by areas, the glyphosate–resistant soybean (Roundup Ready Soybeans) is considered the


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world leading transgenic crop, commercially used first in 1996, estimated to have spread on 41.4 million hectares in 2003, accounting for 61% total areas under transgenic plants. During the first year of the commercially cultivated glyphosate–tolerant maize, roughly 380.000 hectares were estimated to be under glyphosate–tolerant maize in the USA (Talpan, 1998). Apart from soybean and maize, the glyphosate–tolerant cotton and canola are considered the most important crops, economically. The results of numerous experiments suggest applying glyphosate to crops of altered tolerance rather than using standard weed control chemical practices (Moll, 1997).

Glufosinate–ammonium tolerant crops Glufosinate–ammonium is amino salt of amino acid of phosphinotricin

obtained from tripeptid bialafos (L–phosphonotricil–L–alanyl–alanyn). Its mechanism of impact based on inhibiting the enzyme, intrinsic to glutamene synthetase, responsible for synthesis of glutamine acid (Leason et al., 1982), resulted in worsened protein synthesis and nitrogen metabolizm with raised ammonia concentration in the plant cell and, therefore, its raised phytotoxicity. Certain species of the family Streptomyces produce tripeptid bialafos as well as an enzyme protecting the host plant from detrimental effect of its own metabolite.

Further, the so–called BAR gene, isolated from Streptomyces hygroscopicus, is responsible for the tolerance to bialafos, while the gene isolated from S. viridichromogenes encodes the synthesis of phosphonotricin–acetyl–transferasis (PAT gene) for detoxifying phosphinotricin. Both genes are encoding an enzyme for detoxifying glufosinate–ammonium through acetylization of amino group, the first metabolite N–acetyl–glyphosinate being found to have no herbicidal activity. Glufosinate–ammonium – tolerant crops have been attained using BAR or PAT genes (De Block et al., 1987, Donn et al., 1990 a, b). This is referred to as a breeding basis with an array of glufosinate–ammonium–tolerant crops, canola, maize, soybean and sugar beet being the major ones.

Compared with standard herbicides in sugar beet, soybean and spring canola, glufosinate–ammonium provided better efficiency (Rasche et al., 1995), Rasche and Gadsby, 1997). While studying weed control potential with glufosinate–ammonium –tolerant maize under inland conditions, glufosinate–ammonium was estimated to have achieved an effect being at least at the level of standard hebicide combinations if not better when controlling the dominant weeds (Malidza, 2003).

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Imidazolinon– and sulfonilurea–tolerant crops A larger number of crops is deemed intrinsically resistant to a range of

acetolactate synthesis (ALS) inhibitors because their enzymatic system is able to metabolize these herbicides prior to seriously inhibiting the targeted enzyme. Obtaining the imidazolinon- and sulfonilurea–tolerant crops is considered feasible via standard selection modes, coupled with inducing mutations and direct gene transfer. Two modes were used to obtain imidazolinon-tolerant maize. First, pollen mutagenesis helped obtain maize hybrids (the so–called IT) with ALS enzyme being altered, which, as a characteristic, was controlled with one dominant gene (Greaves et al., 1993). Second, contrary to the first mode, the selection in tissue culture with no mutagenous substances used resulted in the highly imidazolinon–resistant maize (IR) as well as in the crossed sulfonylurea– and triazolopirimidin–resistant one (Siehl et al., 1996). IT maize hybrid tolerance in the field conditions was tested using imazetapir in four times higher amount than required for weed control, without noticing adverse effects on the yield (Shaner et al., 1996). IT and IR maize hybrids are commercially used with tendency to grow only IT maize for allowing new genotypes to be bred with ease. In addition, the difference in withstanding acetolactate synthesis between the sensitive and imazetapiron-tolerant IT maize hybrid was seven-fold, with that in IR maize hybrid estimated to be one thousand times higher.

The crucial enzyme in IT maize hybrid showed no tolerance of chlorsulphuron and flumetsulam, whereas IR maize hybrid withstood their 200 to 2200 times higher dose rates than the sensitive maize hybrid did (Siehl et al., 1996). Further, the mutagenesis of microspores allowed the imidazolinon–tolerant spring canola to be obtained, thereby, evolving a new epoch in weed control not only for this plant species but also for the weeds from the family Brassicaceae. Also, wheat seems to be highly economically significant, tolerance of which to imidazolinon was attained through seed mutagenesis (Shaner et al., 1996). Of the leading grown crops, imidazolinon–tolerant sunflower has also paved the way for improving weed control using a wide–range–impact herbicides after crop and weed emergence. A wild sunflower originating from the USA helped breed the imidazolinon–tolerant sunflower, having developed resistance after seven years of using imazetapir on end (Al–Khatib et al., 1998), possessing a key enzyme resistant several times higher to imidazolinon. The mode of inheritance was partial dominance (Miller and Al–Khatib, 2000; Jocic et al., 2001), the total tolerance being attainable only if both hybrid components were homozygous to this trait. Apart from being resistant to imazamox, sunflower could tolerate imazetapir and imazapir, but could not sulfonylurea herbicides (Malidya et al., 2000). Imazamox in the imidazolinon–resistant sunflower has proved to be efficient in controlling dominant annual broad–leafed and grassy weeds (Malidza et


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al., 2002, 2003). Mutant selection ensured a larger number of the sulfonylurea–tolerant plants (Sebastian et al., 1989; Dekker and Duke, 1995).

The sulfonylurea–tolerant soybean (STS) only registered on the US market in 1992 has spread and been applied most widely as yet. The STS crops can simultaneously metabolize herbicide and have higher tolerance to acetolactat synthetase. The increased rates of chlorimuron–ethyl and thiphensuphuron–methyl can be used for weed control in STS soybean (Young, 1997). The active matter of these herbicides may also be applied to the conventional weed control system in the USA, but in lower rates due to lower selectivity. The merit of STS soybean is the higher herbicide dose rates are applied, the higher efficiency is achieved. Moreover, urea and imidazolinon are considered to have suitable ecotoxicological properties, the lower rates of which can be used over a longer period, but invariably effectively protecting from weeds. Limiting factors of using the imidazolinon- and sulfonylurea–tolerant crops are assumed resistant weed growth and rather a constrained crop transfer caused by certain herbicides. Weed resistance develops swiftly and even several years of applying herbicides are required. Thus, in Lactuca serriola, resistance was exerted after five (Mallory–Smith et al., 1990) and in Helianthus annuus after seven years of the unilaterally used herbicide inhibitor ALS–e (Al–Khatib et al., 1998).

Cycloxidim– and setoxidim tolerant maize The herbicides from aryloxiphenoxipropionate and cyclohexandion

groups are being used to control annual and perennial narrow–leaved weeds in broad–leaved crops. The mode of herbicide impact is inhibiting acetil co–enzyme being carboxilasis in monocotiledonous plant species. Maize tolerance of setoxidim, cycloxidim and haloxifop was achieved by selecting mutants in tissue culture via altering sensitivity of the key locus exposed to a herbicide (Marshall et al., 1992; Somers, 1994). The mode of inheriting this trait is partial dominance (Parker et al., 1990). Maize hybrids resistant to setoxidim are being commercially used in the USA (Poast Protected Maize) and establishing those resistant to cycloxidim is on its way in Europe. The herbicides used in the cycloxidim–tolerant maize are paving the way for a more flexible and efficient controlling of Sorghum halepense from rhizome and grassy weeds in maize (Malidza, 2001).

Bromoxinyl–tolerant cotton Cotton resistance to bromoxinyl was attained introducing the gene

intrinsic to bacterium Klebsiella ozaenae, encoding synthesis of the enzyme bromoxinyl, of a specific nitrilasis, responsible for bromoxinyl detoxification (Stalker et al., 1988, 1994, cit. Dekker and Duke, 1995). The presence of this

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gene ensures a high crop resistance to bromoxinyl, withstanding even ten–fold higher herbicide rates than practiced ones. Importantly, this approach contributed significantly to broad – leafed weeds control in cotton due to a shortage of chemical measures and an onset of phototoxicity caused by the existing herbicides.

The merits of growing genetically modified herbicide–tolerant crops

The glyphosate– and glufosinate–tolerant crops seem the most promising thanks to a wide–range impact of such herbicides. Also, the crops resistant to other herbicides (imidazolinon, sulfonylurea, cyclosidim), the resistance of which was built in through conventional breeding modes are promising, too. In general, the genetically modified herbicide – tolerant crops (GMHT) have the following merits: a facilitated and an economically more suitable weed control; a more effective weed control due to weed uncontrollability with herbicides used within the conventionally produced grown crops; herbicide use with higher flexibility; suitability of using herbicides after emergence allowing for a critical period and weed detrimental level; additional potential of controlling weeds resistant to other herbicides and parasitic weeds; potential for achieving higher yields for increased grown plant tolerance to herbicides; lower hazards to the environment through putting the ecotoxicologically more favourable herbicide-tolerant crops into production, and potential of involving alternative production systems (no–till and the like).

A facilitated and economically more suitable weed control One of the most emphasized reasons for increasing (Dewar et al.,

(2000) areas under the individual genetically modified herbicide–tolerant (GMHT) crops is considered a facilitated weed control along with its lower cost rather than being with alternative weed control measures. Using one wide–impact-range herbicide on GMHT crops allows controllability over a large number of weeds without adding any herbicide to extend the existing impact-range. In most cases, the application of solely one herbicide in soybean, maize and sugar beet gives if not better, then at least equal effect to that with combined herbicides in the conventional production. Thus, in the conventional production system of sugar beet, several herbicides are combined reiteratedly, while the GMHT sugar beet receives an equal or even a better effect of glyphosate or glufosinate-ammonium. In addition to being facilitated, weed control costs have also been cut down as well as those relating to glyphosate with soybean, maize and sugar beet, being lower than a much more expensive alternative system of the chemically controlled weeds.


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Thus, as suggested by Dewar et al. (2000), the costs of weed control with sugar beet were estimated to be from 119 and 110 pounds per hectare in Great Britain in 1998 and in 1999, those of glyphosate and gluphosinate– ammonium, used in maximal rates for weed control, from 30 to 60 pounds per hectare. Even though the GMHT seed expenses are higher, their introducing will, hopefully, enable economically more acceptable weed control in the future. Furthermore, areal expansion under the glyphosate-tolerant soybean in the USA gave rise to much reduced costs of the herbicides to be used in the conventional weed control system (Carpenter et al., 2002).

More effective weed control on account of its uncontrollability with the herbicides used within mainstream crop production

Among crucial reasons for introducing GMHT crops lies an answer to the recent problems encountered in weed control, such as resistance of weeds to dominant herbicides and weeds, belonging to the same family as the grown crop does, on which the available herbicides have no or poorer effect than those efficient with GMHT crops. Therefore, introducing GMHT crops will be promising for controlling a range of perennial and other weeds similar to a grown crop, rather than lowly efficient existing selective herbicides used in the mainstream crop production. Dewar et al. (2000) pointed out the significance of the glyphosate-resistant sugar beet in which self-emerging potato will be effectively controlled and the number of nematodes in the succeeding crops reduced at lower costs. As suggested by May (2003), within a crop, it is easier to control Cirsium arvense as well as other weeds at lower costs. Also, Sorghum halepense, Asclepias syriaca and other problematic weeds with the glyphosate-tolerant soybean have been proven controllable with notable success in the USA (Culpepper et al.; 2000; Pline et al., 2000). Numerous examples substantiate an effective controllability of problematic weeds, such as those from the family Brassisaceae in canola (Merker et al, 2004), followed by Xanthium strumarium in sunflower after emergence (Malidza et al., 2003), Cynodon dactylon in maize (Malidza and Bekavac, 2001) etc. Evidently, weeds could be highly controllable in GMHT crops, which is illustrated best by the fields under the crops considered.

Herbicide use with higher flexibility The higher GMHT crop tolerance of herbicides allows their delayed

application since the crops exhibit tolerance to them in later phases of the grown crop development (glyphosate, setoxidim, cyclosidim, gluphosinate–ammonium). For example, glyphosate in glyphosate–resistant maize may be used last of all the available herbicides (Carpenter et al., 2002). As far as herbicide use timing and crop and weed growing phase are concerned, the

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flexibility of glyphosate and glufosinate–ammonium use in the GMHT sugar beet seems significantly advantageous rather than being with other herbicides in this crop (Dewar et al., 2000).

Suitability of using herbicides after emergence allowing for a critical period and weed detrimental treshold

Speaking about crop growing phase, herbicide application in GMHT plants is likely to be highly flexible, with herbicides applied after emergence only if meeting economical requirements. Such a lawfulness applies not only to the conventionally used herbicides, but also to the individual GMHT crops for potential herbicide use throughout later GMHT crop and weed growing phases (Hurle, 1998; Martin et al., 2001).

Additional potential of controlling weeds resistant to other herbicides

Dominant herbicides used in the leading grown plant species embrace the representatives of triazin, chloracetamid, carbamide, sulphonilurea, imidazolinon, aryloxiphenoxipropionate, cyclohexandion groups, with a huge number of the weed resistant biotypes evidenced so far (Heap, 2004). Considering that glyphosate and gluphosinate–ammonium were not used on considerable areas in the crop production in the past, they may additionally help control weed resistance to the remaining herbicides. The potential of controlling Helianthus annuus resistance to acelolactat synthetase may serve as an illustration. That soybean has developed its resistance to the herbicides dominating this weed is a well-known fact in several countries of the USA, glyphosate more efficiently controlling soybean than all the alternative herbicides do in the glyphosate–resistant soybean (Allen et al., 2001).

The potential of achieving higher yields for increasing grown plant tolerance to herbicides

Under stressful environmental conditions, herbicides cause no adverse effects in the GMHT crops unlike frequent ones relating to the conventionally produced crops (Burnside, 1996). With the imidazolinone and sulphonilurea herbicide groups resistant crops, the risk of extended adverse effects caused by more persistent herbicide representatives to the succeeding crops may be reduced over their setting (the imidazolinone-resistant canola, maize and sunflower as well as the sulphonilurea–resistant soybean and the like).

The potential of parasitic weeds control The parasitic weeds from the family Orobanche and Striga occupy over

100 million hectares in the African and Mediterranean countries, thereby


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largely constraining the production of a greater range of sensitive grown crops (Gresset, 2000). Introducing single HT crops and using glyphosate and acetolactat synthesis inhibitor can visibly reduce the adverse effects of the weeds considered (Gressel, 1996). More than 100 million farmers in Africa have been found to loose more than a half of the total maize production due to weeds from the family Striga (Berner et al., 1995). Growing the imidazolinone–resistant maize and seed treatment with imazapir confirmed the potential for controlling parasitic weeds Striga hermontica and S. asiatica and 3–4 times higher increase in yield (Abayo et al., 1998, Kanampiu et al., 2003). In addition, introducing the imadadozilinone–resistant sunflower favoured the control of Orobanche cernua. The potential of concurrent controlling this parasitic weed and the dominant weeds in the imidazolinone-resistant sunflower was also substantiated (Malidza et al., 2003).

Lower hazards to the environment by putting the ecotoxicologically more favourable herbicide-resistant crops into production

Glyphosate, glufosinate–ammonim, imidazolinons, sulphoniluree and cyclohexandions are considered to have suitable ecotoxicological properties, which will, when coupled with the previously mentioned ones, contribute to lower hazards to the environment. As calculated by Wauchope et al. (2001), replacing atrazin and alachlor with glyphosate and glufosinate–ammonium when introducing the genetically modified maize toward these herbicides, is likely to reduce the risk to groundwaters contamination. Since as lower glyphosate and glufosinate–ammonium dose rates as possible were attempted, only one fifth up to one tenth of the alachlor and atrazin concentration was therefore leached into deeper soil layers.

Potential of introducing alternative production system Tending to use as economically acceptable production system as

possible, the farmers in North America have been massively adopting some of the GMHT crops, highlighting their suitability for improving no–till production system. Thus, the areas using no–till production system have been expanding in the USA since the glufosat–resistant soybean came into life. The glyphosate – tolerant soybean grown in no–till production mode allowed weed control in the crop per se, to be more effective, whereas prior to introducing glyphosate–tolerant soybean, glyphosate had been used before sowing and emergence for controlling the existing weeds. Within no–till production system, the glyphosate- and glufosinate–ammonium resistant maize did not exclude using other herbicides and the best results have been accomplished combining glyphosate and soil herbicides before sowing with herbicides used after emergence (Helwig et al., 2003). In addition to no–till system, the tendency of producing soybean with a higher number of crops per

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unit area is increasing. So cultivated glyphosate–resistant soybean requires a lower number of treatments with herbicides due to different conditions under which weeds grow (Norsworthy and Oliver, 2001; Reddy, 2003). Also, introducing some of the GMHT crops will allow herbicides to be used when cultivating combined crops tolerant of the same herbicide, such as cyclo–oxide–tolerant beans and maize.

Potenatial hazards to the genetically modified herbicide-tolerant crops

Despite numerous advantages of GMHT crops, encouraging their cultivation does not necessarily mean a complete absence but inevtiably present hazards. Increasing dependence of farmers on herbicides is becoming a serious concern which will either set other measures back or put them out of practice. Moreover, new mainstream of herbicides and other policies developed for weed control are expected to be legging behind and ignored. Importantly, the gravest anxiety related to GMHT crops is associated with gene transfer to wild allies as well as with resistant weeds growth. Therefore, due to genetic variability of crops and chemical variability of herbicides, we cannot generalize hazards. As in previous cases, each case (crop, herbicide, wild allies and the like) should be regarded per se in light of the potential hazards and within single cases taking the following into account:

• Which advantage over production of every single crop affords an additional character of tolerance to a particular herbicide?

• What is the likelihood and which are the consequences of gene transfer responsible for weed and wild allies resistance?

• What is the likelihood and which are the consequences of self-emerging plants or weeds on the rudumentary habitats as the problem encountered in the agroecosystem?

As suggested by previous authors, gene source is unimportant for its tolerance to herbicide when assessing the hazards considered, i.e. whether tolerance resulted from mutations within a grown crop or from the gene coming from another organism. From the other stakeholders’ points of views, such as consumers and producers, neither gene source nor the herbicide – tolerant crop mode production is that relevant for such hazards for the time being. The transfer of genes responsible for tolerance of herbicides may enhance weeds viability and adaptability to farming and non-farming areas.

In addition, weeds are likely to receive the characters intrinsic to invading species, which is however more relevant to the genes responsible for insect resistance or disease causals.


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Development of resistant weed biotypes as a result of GMHT grown areas expansion and of intensified use of lower herbicide number on larger areas

Weed resistance to herbicides is a genetic phenomenon, being an example of weed expedited evolution and their intrinsic power to survive. The process had a long genesis before herbicide–tolerant genetically modified crops. Expanding GMHT canopies using several wide range–impact herbicides suggests a faster developing potential of the weed biotypes resistant to dominant herbicides. 286 resistant biotypes have been recorded in 171 weed species in the world so far (Heap, 2004). An evidence about weed biotypes resistant to glyphosate in 6 weed species (Heap, 2004) may be threatening when considering a future crop ranking tolerance to this herbicide. Lolium rigidum and Eleusine indica developed tolerance to glyphosate prior to introducing GMHT crops (Powles et al., 1998). Thus, the first resistant biotype Conyza conadensis was registered in the USA after three years of glyphosate application in soybean (VanGessel, 2001). More resistant weed biotypes can be precluded or delayed using combined herbicides of different impact fashion (Diggle et al., 2003). The same authors suggest this strategy being more efficient than herbicide rotation of different exhibiting effect manner. More frequently occurring resistant weed biotypes over the recent years entail a serious threat to individual GMHT crops, suggesting their sustainability to be tended over a longer period of time, but solely as the part of an integrated weed control management (Knezevic and Cassman, 2003).

Gene transfer from the GMHT to wild allies and weeds Weed resistance is mainly the onset of selection within a particular

weed population in conditions of reiteratedly used herbicide, where gene transfer from a grown crop tolerant to a particular herbicide to plant allies is an additional possibility. Those who deny GMHT crops mainly stress that such a risk stems from the very centre of origin of grown crops in single cases. This instance of risk has appeared in maize in central America, but appears to be insignificant in other areas. Gene transfer is likely to occur only between the sexually congenial plant species. Keeler et al., (1996) listed only 11 of 60 grown plant species worldwide not to possess any wild allies. Of 13 leading grown plant species, 12 were proven to natuarlly hybridize with wild cognates (Ellstrand et al., 1999, cit. Wolfenbarger and Phifer, 2000). Cultivating GMHT crops can increase crossing potential with compatible species, thereby enhancing the adaptability of the latter to farming and non-farming ecosystems. In general, most of the grown crops are regarded unable to remain viable unless helped by man, with their abilities to survive being however differing from species to species. Being as much adaptable to the

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ecosystems as the herbicide-unresistant crops are, the herbicide–resistant ones bear no advantages over the other crops in the absence of herbicides within an ecosystem (Thill, 1996). Further, as a result of gene transfer, a wild ally of a grown crop is likely to acquire the traits intrinsic to the invading species. The herbicide–tolerant grown crops do not possess more expressed traits of the invading species than their non–transgene forms and wild allies do. Accordingly, direct or indirect impact and control over invading species have been estimated to roughly 137 billion dollars solely in the USA per annum (Pimentel et al., 2000, cit. Wolfenbarger and Phifer, 2000). Since 2003, the grown sunflower resistant to imidazolinonim has been cultivated in the USA. Transfer of the gene, responsible for tolerance of sunflower to imidazolinonim, to a wild ally was confirmed by Massinga et al., (2003).

Wild sunflower (Helianthus annus) served as a gene donor for tolerance to imidazolinonim while breeding the grown sunflower, only the spontaneity of gene transfer in the opposite direction being currently stressed. Also, that gene for tolerance of wheat (Clearfield) to imidazolinonim may be transferred to the weed Aegilops cylindrica through hybridization in natural conditions was revealed by Snyder et al., 2000; Andesron et al., 2004. The resistance of Aegilops cylindrica in monoculture of the wheat resistant to imidazolinonim was found by Hanson et al., (2002) to develop in less than 10 years without and in a much shorter time than that with wheat hybridization.

Genetically modified and herbicide-tolerant crops as volunteers in succeeding crops

This is often emotionally referred to as „super–weed“ by extreme opponents, emphasizing the risk this technology bears. That grown crops becoming weeds in the succeeding crops for being linked with each new herbicide introduced into plant production system, seems nothing of a new problem. The results obtained in controlling self–fertilized grown plants in the succeeding ones at the start of growing canola tolerant to glyphosate, glufosinate–ammonium and imidazolinone appeared to be encouraging. However, that the spring canola (Brassica napus), being simultaneously resistant to glyphosate, gluphosinate–ammonium and imidazolinone, had emerged by spontaneous crossing in Alberta (Canada) was substantiated by Hall et al. (2000). This is a good example depicting hazards due to an intermingled resistance toward several herbicides of the congenial foreign– fertilized crops that might be as problematic as self-fertile crops are in the ensuing crops. In this case, an integrated crop rotation and herbicide management along with combining herbicides and other measures for preventing further progress of such occurrences and adverse effects of self – fertile crops, B. napus, with multiple resistance to herbicides may be recommended.


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Increasing hazard of damaging untargeted plants using a wide–impact–range herbicide

Increasingly cultivated GMHT crops have also increased hazards of the wrongly used herbicides to the crops, not being resistant to a particular herbicide, and those of the herbicide solution drift on the susceptible ones. Damages to crops due to wrongly applied herbicides (the application of herbicide to which crop is not resistant) will occur, but the reasons for this should not be sought in increasing areas under the genetically modified crops tolerant to herbicides. Herbicidal drift on untargeted plants appears to be constant, which, with optimizing water amount for herbicide use, may be minimized (Ellis et al., 2002).

Potential influence on biodiversity GMHT crops are gravely threatening biodiversity. If largely grown,

such crops may even change the existing biodiversity of the agroecosystems subjected to an intense and biased use of the individual cropping practices. Thus, the relationship between growing genetically modified sugar beet tolerant to glyphosate and the number of birds, the species Alauda arvensis, was studied in Great Britain. It is expected that further decline in the number of this species will depend on a better controllability of Chenopodium album in the GMHT sugar beet, the seed of which provides this species an important food source (Watkinson et al., 2000; Dewar et al., 2002, 2003). Of 13 million hectares, 98% accounted for the glyphosate–tolerant soybean grown in Argentina in 2003 (James, 2003), its immense growing, giving rise to a fall in glyphosate prices (3 dollars per litre of glyphosate) expanding its application to non-farming areas. Over– and recap use of glyphosate (even of up to 16 l/ha/year) caused weeds to entirely disappear not only around the soybean field and in the soybean crop itself, but also in all the areas treated with glyphosate being temporarily unused for plant production. In 2000, more than 100 million litres of glyphosate were applied accordingly in Argentina. Biodiversity is assumed to have largely been jeopardized by an excessively used glyphosate on the larger areas rather than by the genetically modified glyphosate–tolerant soybean (Leguaizamon, 2001).

Changes in weed flora Having created their own systems in weed control, agricultural

producers are using those measures which, in their opinions, render optimal results. Since weeds adapt to every production system, a good farming practice may well postpone their adverse effects and the would–be lost advantages of recent technologies. Unless GMHT crops are used as the part of integrated weed control system, an expected scenario will be an altered weed floral composition and growth of its resistant biotypes (Knezevic and

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Cassman, 2003). Being so, the best optimality will be ensured by co–presence of the GMHT crops, the herbicides, to which crops exhibit tolerance, other herbicides and weed control measures, too. Even though a wide–impact–range herbicides (glyphosate, gluphosinate-ammonium) are being applied to the individual, presently, commercialized GMHT crops worldwide, weed flora is being likely to change by encouraging the naturally more resistant weeds to such herbicides and by increasing weed sharing, too (VanGessel, 2001). When introducing individual crops, farmers risk resting, primarily, on the herbicides, so putting the mainstream weed control measures out of use.

Prospects and future of the genetically modified crops in Europe

The herbicide–tolerant genetically modified crops entail an additional option to farmers when controlling weeds, which would be appropriately used only if incorporated into integrated weed control management (Malidza et al., 2005).

A rapidly increasing area stretch underneath the herbicide–tolerant genetically modified crops envisages changes to be on their way in Europe (Agrow, 2003).

That genetically modified crops are advantageous is doubtless. However, their use should be approached with utmost care because little is known about possible implications and adverse effects such crops may imply. The use of transgenic crops for scientific purposes is allowable in the country, their further ranking hugely depending on the EU one.

Table 4. Forecast of GMHT crops participation in European Union to 2013 (Agrow, 2003)

Crop First year of production

% of area planted to a particular crop in

2008

% of area planted to a particular crop

in 2013

Maize 2005–2007 10 35–45

Oilseed rape 2006–2008 0–5 20–30

Soybean 2007–2009 0–10 30–40

Sugar beet 2006–2008 5–10 40–50

Wheat 2008–2011 0 15–25

Rice 2007–2009 0–5 30–40

Cotton 2006–2008 5–10 40–50


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The issues considered are being discussed at meetings such as Codex Alimentarius, OECD Seed Schemes, Convention on biological divergence-CBD, with regulations varying from country to country, from complete prohibition of GMHT crops, GMO in Algeria to their full liberalization in the USA and in Argentina and de facto moratorium in EU countries (Masirevic and Bugarski, 2004). In light of GMHT crops, the EU countries deserve special mention. The fact that 22,000 ha of maize, i.e. 2,000 ha BT maize had been sown in Spain and France in 1998, was pressurized by public opinion, opposing not only the GMHT crops introduction but also the new transformant experimentation after the initiative had been made by Denmark, Greece, France and Luxembourg, so bringing them to a standstill (Phipps and Park, 2002; Bekavac et al., 2004).

However, the moratorium in the EU countries due to application of GMHT crops was even more tangled when the USA said it would lodge a complaint to the World Trade Association, accusing the EU of having based such a moratorium on the entirely unscientific principles, giving no good reasons for it any longer. Still, denying GMHT crops by EU seems to have eased up with more optimism shown recently. In 2002, the EU legalized banning the moratorium, some of its members still hanging on of whether or not to accept the GMHT crops and pondering their being tightly linked with numerous factors.

Despite the existing scenarios for the GMHT crop technology adaptation approaches, GMHT crops are expected to share 10% total EU agricultural areas in the next 5 years, during which time, GMHT crops ought to be validated, enlisted, some of their traits–introduced into the commercially most important varieties and hybrids (Bekavac et al., 2004).

Overall, in the next ten years, the GMHT crops are expected to share EU areas, but depending on production specificities from region to region (weeds and pests) as well as on those from crop to crop (BioPortfolio, 1997–2003).

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Instruction to Authors in Herbologia

One copy of manuscript in English should be submitted by e-mail or as a hard (paper) copy and a floppy disc.

Manuscripts should be computer typed in MS Word, single spaced, on the page (paper) format of B5, font of Times New Roman, font size 12 (keywords and list of references with font size 10). The text lines should be justified. The length of the paper can be up to eight pages.

The paper should start with the title of the article, the names of each author, his/her institution, address and e-mail address.

Abstract would not exceed 300 words or 20 lines. Keywords, up to two lines long, should be listed below the abstract.

Main text includes intruduction, materials and methods, results and discussion. Footnotes should be avoided. SI units should be used. Reference list should be ordered alphabetically. Examples: AUTHOR, X.Y. & Z.Q. AUTHOR, 2001: Title of article, Journal title in Italics, 12, 78-84. Or: AUTHOR, A., B. AUTHOR, 1998: Book title (ed. GH Editor). Publisher, Place, Country.

Figures and tables should be numbered consecutively and should have an appropriate caption or legend.

Scientific names should be in italic. When a plant name is repeated, it can be abbreviated, e.g. C. album. For crop plants, common English names are used, but the scientific name can be given in parentheses at the first mention in the main text, e.g. oats (Avena sativa). Both British and American forms of common names can be used (e.g. corn and maize, alfalfa and lucerne etc.), up to the choice of the author. For herbicides and other chemicals, in Materials and methods, one should state common approved names and trade names, e.g. glyphosate (Roundup 360 a.i. L-1, Monsanto), and thereafter only trade names. Dose of herbicides should be expressed in terms of active ingredient (e.g. a.i. ha-1).

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