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The effect of plant ageand soil amendments onseverity of phytophthoraroot rot of pepper(Capsicum annuum L) inSouth Western NigeriaA. C. Odebode a b & K. Shehu aa Department of Botany and Microbiology ,University of Ibadan , Ibadan, Nigeriab Department of Botany , University of Dares Salaam , P.O. Box 35060, Dar es Salaam,Tanzania E-mail:Published online: 15 Dec 2008.

To cite this article: A. C. Odebode & K. Shehu (2001) The effect of plant ageand soil amendments on severity of phytophthora root rot of pepper (Capsicumannuum L) in South Western Nigeria, Archives of Agronomy and Soil Science,47:3-4, 363-369, DOI: 10.1080/03650340109366219

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Arch. Acker-Pfl. Boden., 200t, Vol. 47, pp. 363-369 © 2001 OPA (Overseas Publishers Association) N.V.Reprints available directly from the publisher Published by license underPhotocopying permitted by license only the Harwood Academic Publishers imprint,

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THE EFFECT OF PLANT AGE AND SOILAMENDMENTS ON SEVERITY

OF PHYTOPHTHORA ROOT ROTOF PEPPER (CAPSICUM ANNUUM L)

IN SOUTH WESTERN NIGERIA

A. C. ODEBODE* and K. SHEHU

Department of Botany and Microbiology, University of Ibadan,Ibadan, Nigeria

(Received 4 April 2001)

The incidence and severity of pepper Capsicum annuum to phytophthora root rot caused byPhytophthora infestan in Southwestern Nigeria was investigated. Root rot incidence and severitywas significantly reduced with increase in the plant age. The highest level of root rot, of 81.7%and 67.6% obtained in 4 and 6 weeks old pepper plants were reduced to 25% and 5% in 10 and12 weeks old pepper plants respectively. The resistance of the pepper plant to root rot severityincreased with age. The result also showed that amendments of the soil with chicken manurewood ash and neem leaf suppressed the root rot incidence and severity of disease in the pepperplant.

Keywords: Plant age; Soil amendments; Phytophthora; Root rot; Severity and pepper

INTRODUCTION

Pepper is usually a suitable host for large number of plant pathogens whichcould cause significant damages and could limit the entire pepper produc-tion in areas of intensive cultivation. Principal diseases are root rot and wiltdiseases caused by soil borne pathogens (Marinkovic et al., 1992, Kimble

*Address for correspondence: Department of Botany, University of Dar es Salaam, P.O. Box35060, Dar es Salaam, Tanzania, e-mail: ode@amu.udsm.ac.tz

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364 A. C. ODEBODE AND K. SHEHU

and Grogan, 1990; Kim and Hwang, 1992; Odebode et al, 1995, 1997).Phytophthora root rot of pepper which is caused by phytophthora speciesis the most devastating soil borne disease of pepper throughout the world.(Bowers and Mitchell, 1991; Riley and Bosland, 1995; Hwang, 1995). Mostfrequently reported Phytophthora capsici which incites pepper root rot (Kim,1989; Bosland and Lindsey, 1991; Hartman and Wang, 1992;Ristainoefer/.,1994).

The effect of age on the susceptibility of plants to fungal disease havebeen studied extensively (Cook, 1980; Koh et al., 1987; Hwang and Kim,1990; Prabhy and Fillipi, 1995). The susceptibility of leaf and panicle to blastcaused by Pyricularia oryzae has been shown to decrease with increasing ageof the rice plant (Roumen etal., 1992; Prabhu and Fillipi, 1995). Similarlydecreased susceptibility to Puccinia arachidis with plant age in groundnuthas been reported (Cook, 1980). This paper reports on the effects of age onthe resistance of pepper to phytophthora root rot caused by Phytophthorainfestait and control by soil amendment in South Western Nigeria.

MATERIAL AND METHODS

Plant Materials and Inoculation

Pepper (Capsicum annuum) seeds used in this study were obtained locallyfrom a market in Ibadan, Nigeria. The seeds were surface sterilized with95% ethanol and rinsed in several changes of sterile distilled water beforesowing. The seedlings were raised in trays (35 x 15 x 10cm) filled withloamy top soil sterilized at 121°C at 1.05 kg/cm2 for 1 hour. Seedlings weretransplanted after 2 weeks into plastic pots (20 cm diameter and 30 cm deep)filled with sterilized soil. The seedling were watered daily.

Phytophthora infestan was isolated from the farms located in the Univer-sity of Ibadan, by using the baiting technique of Nelson and crafts (1991).Pure culture of the isolate was obtained by continueos sub-culturing onpotato dextrose agar (PDA). The pathogen inoculum was prepared as sporesuspension obtained from 7 day old cultures. The appropriate concentra-tion was measured by using the Hewskley haemocytometer. The pepperseedling were inoculated at age( 2,4,6,8, and 10) weeks after sowing, usinginoculum technique described by (Marinkovic et al., 1994 and Odebode,etal, 1995).

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ROOT ROT OF PEPPER 365

Soil Amendment

Chicken manure, neem leaf and wood ash were used as soil amendments.Each of this material was mixed with dried loamy soil at rate of 1:3 (v/v)and then sterilized at 121°C 1.05 kg/cm2 for one hour prior to use. Threeseedlings were transplanted into plastic pot, containing amended soil with atwo weeks rentention time. Non amended soil served as control. Three repli-cate pots were prepared for each treatment. Controls consisted of a set of noninoculated pots for each age treatment and a set of inoculated unamendedsoil. Fungal populations in the amended soils and the control were deter-mined by dilution plates method of Osunlaja (1989), using a soil dilutionof 10~3 on potato dextrose agar to which the antibacteria supplement strep-tomycine had been added. The fungal colonies were counted on countingchambers, multiplying the numbers of colonies by dilution factors to obtainnumber of colonies per gram of soil.

Disease Assessment and Scores

The pepper seedlings were assessed for symptoms typical of phytophthoraroot rot disease, such as chlorosis of leaves, stunted growth, wilting andbrownish roted roots (Hartman and Wang, 1992; Hwang and Kim, 1995;Muhammad et al., 1995). Two weeks after inoculation the seedling now atages 4, 6, 8, 10, 12 were assessed for symptoms.The plants were scoredfor severity of disease with intensity increasing from 1 to 5, where 1 isasymptomatic plants 2 is form 1 to 25% root area infected, 3 is from 26 to50% of the root area necrotic, 4 is form 51 to 75% and 5 is from 75 to 100%of the root infected

Data Analysis

Treatment were laidout as a completely randomized design with three repli-cation. Microbial population data were analyzed by analysis of variance.Means were separated by using the LSD test.

Result

The effects of age on phytophthora root rot caused by Phytophthora infes-tan is shown in (Tab. I). The number of plant stands that showed wilting

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366 A. C. ODEBODE AND K. SHEHU

TABLE I Relationship between plant age and Disease severity of pepper (capsicum annuum)caused by Phytophthora infestain

Age ofplant(weeks)

Control4681012

No. of plantshowingchlorosis

09g530

No. of plantstunted

099820

No. ofwiltedplant

097420

Percentageroot rotseverity

0.0081.6767.6748.3325.005.00

Precentageplant

resistance

0.0016.3332.3351.6775.0095.00

* Age of plants in weeks at the time of assessment for symptoms.Data are means of 3 replicates of 3 seedlings per pot.

chlorosis and stunting decreased as the plant age increased. The root rotseverity decreased from 81.7% in 4 weeks old pepper plant to 5% in 12weeks old pepper plant. The same range of wilting was observed for wiltingincidence in the pepper plant. There were significance differences in plantage in relation to root rot and severity at 0.5 level of probability by LSD test.

The effect of soil amendments on root rot severity showed that chickenmanure and wood ash amended soil, significantly reduced root rot severityfrom 60% in 4 weeks old pepper plant to 1.70% in 12 weeks old pepperplant (Tab. II) and the amendment also increased fungal population in thesoil with chicken manure having the highest fungal population (Tab. II).The fungal isolates from the amended soils were, Pénicillium cyclopium,Pénicillium notatum,Trichoderma harzianum, Fusarium solani, Mucor spp,and Aspergillus niger. The analysis of variance data for amendment treatmentshowed a significance difference of 0.01%.

DISCUSSION

The result showed that the degree of susceptibility to Phytophthora infes-tan; measured in terms of root rot severity and percentage wilt incidencedecreased with increasing age of the pepper plant. The altered susceptibilityto fungal diseases has been reported in several crop plants (Savary, 1987;Roumen et al., 1992; Prabhy and Fillipi, 1995). For example, the suscepti-bility of the rice plant to blast infection was reported to be greatest in theplant aged; 32-39 days (Prabhy and Fillipi, 1995) similarly phytophthora

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ROOT ROT OF PEPPER 367

TABLE II Effect of soil amendments on root rot severity of pepper caused by Phytophthorainfestait and microbial population in the amended soil

Soilamendments

Chicken manure.Wood ashNeem leafUninoculatedcontrol.Unamendedinoculatedcontrol

4

60.0065.0081.6785.50

100.00

Percentage root rot plant age*

6

56.0063.3370.6773.67

100.00

8

46.6751.6753.0060.00

90.45

10

19.3321.6723.2740.27

90.00

12

1.703.306.00

15.00

60.00

PHofameded

soil

5.55.06.56.5

6.5

Microbialpopulation

CFU/gamended soil

190.00+156.67+87.67 ns83.30

83.30

* Age of seedlings at the time of assessment for root rot severity.* Significantly different from control at P=0.005 by LSD test. N.S not significant.

blight of pepper, caused by Phytophthora capsici has been reported to gradu-ally decrease with increasing age of the pepper plants (Kim et al., 1989).Hwang (1995) in a related study has demonstrated that a phytoalexin cap-sidiol, present in infected roots, stems and fruits of pepper plants accumulatedto high levels as plants matured. In comparison, with the infected organs,the resistant cultivars always contained more capsidiol than the suscepti-ble cutivars, suggesting that capsidiol production appears to have a role inincreasing the resistance of pepper plant with ageing.

In the present study similar disease reactions were observed with increas-ing age of the pepper plants. Root rot starting with high severity levels in 2weeks old pepper plants was reduced significantly in 6-12 week old plantsat 0.0001 probability level. Similarly there was a significant reduction in per-centage wilt incidence (PWI) due to high disease severity. The coefficient ofvariation in both series of the measurement were relatively small suggestingthat the dependant variable is a reliable response. Savary (1987) in a relatedstudy with groundnut reported that infection efficiency of the rust (Pucciniaarachidis) decreased from younger to older seedlings.

The evaluation of disease severity control through age related resistancecould be of practical importance in the plant disease management strategy inaddition to its value in resistance testing under field conditions. Late plantingof pepper seedlings is not generally recommended because of greater suscep-tibility of the young plants to soil-borne plant pathogens and unfavourableweather which promote rapid disease development leading to the death ofplants. And consequently reduction in yields.

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368 A. C. ODEBODE AND K. SHEHU

The effectiveness of soil amendment in controlling soil-borne plantdisease was well documented (Osunlaja, 1989; Oritsajafor and Adeniji, 1990;Hadar and Mendaelbaum, 1992; Vos and Duriant, 1995). In this studywith the exception of neem leaf amended soil significant differences inthe amended and un-amended treatments were observed. With the excep-tion of neem leaf soil mixture, the microbial populations were stimulatedby the soil amendments. The fungal populations were particularly higherin suppressive amendments. This was especially true for chicken manure.Although no clear relationship between fungal populations and disease sup-pression was investigated further, the elevated levels of fungal populations inthe amended soil may be a major factors. The pH of amended soil especiallythat of chicken manure and wood ash increase, which makes it favourable forfungal growth. It is possible that the elevated levels of microbial populationresults increased competition between amended inhabiting fungi and phy-tophthora spp for root excudate components essential for the germinationof phytophthora propagates and mycelia growth (Nelson, 1990; Baker andDunn, 1990). This could be responsible for the suppression of Phytophthorainfestan in this study.

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