Eur. J. Agron., 1993, 2(2), 83-91

Abstract

INTRODUCTION

Growth, grain yield and water use efficiency of tritordeum in relation to wheat

M. Gallardo (') and E. Fereres (2)

CIDA and University of Cordoba, Apdo 4240, 14080 Cordoba, Spain. (2) Present Address : Ministerio de Educaci6n y Ciencia, Serrano 150, 28006 Madrid, Spain.

Accepted 12 March, 1993.

(I) To whom correspondence should be addressed.

In the search for alternative crops suitable for rainfed mediterranean cropping systems, a new spe­cies of cereal x Tritordeum Ascherson et Graebner (Hordeum chilense Roem. et Schultz. x Triticum spp.) has been bred by crossing a wild barley with bread and durum wheats. The productivity and agro­nomic characteristics of two experimental lines of tritordeum in relation to wheat were evaluated at Cordoba (south-western Spain) in the 1986/87 and 1987/88 growing seasons. In 1987/88, an early and a later release of tritordeum (recombined and secondary tritordeums) were compared to an early-matur­ing bread wheat (cv. Cajeme) and a late-maturing durum wheat (cv. Ardente) in terms of tiller and biomass production, harvest index, yield and yield components, evapotranspiration (ET) and water use efficiency (WUE). Only the recombined tritordeum was evaluated against the same early bread wheat and a late bread wheat (cv. Mara) in 1986/87. In 1987/88, both tritordeums and the late wheat had similar phenological development, reaching anthesis about two weeks after the early wheat. Above­ground biomass of secondary tritordeum was similar to both wheats (around 1300 g m-2) while recom­bined tritordeum produced only 905 g m-2 of biomass. Grain yield of recombined and secondary tri­tordeums were 23 and 58 per cent of the average yield of both wheats which were similar to each other (5.5 t ha-1

). ET was similar for all four genotypes. Consequently, biomass WUE was less in recom­bined tritordeum than in the other three genotypes (2.3 vs. 3.3 g m-2 mm-1), while WUE in terms of yield was lower in both tritordeums than in the wheats. In both years, tiller production was 30 to 75 per cent higher in the tritordeums than in the wheats. The lower yields of the tritordeums were primar­ily due to a much larger number of unproductive tillers and to a lower mean grain weight. The large yield improvement in secondary tritordeum relative to recombined tritordeum was due to an increase in biomass and in number of grains per ear. These agronomic characteristics, high grain protein con­tent and the considerable improvement achieved through several generations of breeding suggest that tritordeum may be a valuable alternative winter cereal in mediterranean environments.

Key-words : new cereal, tritordeum, wheat, mediterranean environment, water use.

pose cereal, which could be used for forage and/or grain production in marginal areas, depending on the amount and distribution of rainfall.

A new species of cereal, x Tritordeum Ascherson et Graebner, was developed by crossing a wild South American barley (Hordeum chilense Roem. and Shultz.) with cultivated bread and durum wheats (Martin and Cubero, 1981). One notable feature of tritordeum is its high protein content of 18 to 25 per cent of grain weight (Martin, 1988), which is much greater than that of wheat or triticale. The high pro­tein content of tritordeum may be of considerable value to plant breeders and as a protein source for livestock (Cubero et al., 1986). Breeders have also noted the potential of the new species as a dual-pur-

Previous studies of tritordeum have assessed cyto­logical and genetic aspects (Padilla and Martin, 1987 ; Millan et al., 1988), but the agronomy of tritordeum under field conditions is unknown. Knowledge of the agronomic performance of tritordeum is necessary for its general evaluation, ideotype design for future breeding and for the selection of suitable cropping environments.

In this study, crop growth and development, grain yield and the water use efficiency of two experimen­tal lines of tritordeum were evaluated in relation to an

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84

early and two late wheats. The late wheats are local cultivars previously grown in the Cordoba region of Spain and the early wheat, in current use, is represen­tative of early maturing cultivars. The study was con­ducted in the mediterranean climatic region of south­western Spain where water limitation after anthesis is commonly a major constraint to dryland cereal pro­duction. The suitability of tritordeum for mediterra­nean conditions is assessed.

MATERIALS AND METHODS

Location

Two field experiments were carried out over two successive seasons (1986/87 and 1987/88) at the Agricultural Research Centre at Cordoba, south-wes­tern Spain (37.8 °N, 4.8 °W). The soil at the experi­mental site is a sandy-loam, classified as typic xero­fluvent. Field capacity (drained water content) is 0.23 cm3 cm-3 and the wilting point (15 bars) is 0.07 cm3 cm-3•

Experimental design

In both growing seasons, tritordeum (Hordeum chi­tense Roem. and Shultz. x Triticum spp.) was com­pared with two wheat genotypes. The plots were 10 m x 2.8 m in 1986/87 and 15m x 2.8 m in 1987/88. There were 14 rows in each plot, spaced 20 em apart ; the planting density was 300 plants m-2 in 1986/87 and 250 plants m-2 in 1987/88. There were four replicated plots of each treatment, sown in a ran-

M. Gallardo and E. Fereres

domised block design. The experimental area was sur­rounded by a 20 m wide buffer zone sown to wheat. The sowing dates were 29 November 1986 and 22 December 1987. Continuous heavy rainfall in autumn 1987 resulted in a comparatively late sowing in the 1987/88 experiment.

The origins of the tritordeums (parental lines of H. chilense and wheat) and the wheat genotypes used in the experiments are presented in Table 1. In the 1986/87 experiment, an early released experimental line of tritordeum (HT5), here referred to as recom­bined tritordeum, was compared with an early-matur­ing bread wheat (cv. Cajeme) and a late-maturing bread wheat (cv. Mara). The recombined tritordeum is a line derived from crosses between two primary tritordeums and selected by a pedigree method. In the 1987/88 experiment, the recombined tritordeum and an improved line of tritordeum (HTCl), here referred to as secondary tritordeum, were compared with the early-maturing bread wheat (cv. Cajeme) and a late­maturing durum wheat (cv. Ardente). The secondary tritordeum was the product of five further generations of breeding by selfing and selection. In both the recombined and the secondary tritordeum, the cyto­plasm used derived from H. chilense. The secondary tritordeum was not used in the 1986/87 experiment because of the limited amount of seed available.

Phosphate and potassium fertilizers were applied to all plots immediately before sowing at rates equiva­lent to 85 kg P ha-1 and 42 kg K ha-1• A total of 150 kg N ha-1 as urea was applied as an equal split dressing at sowing and tillering (approximately 50 days after sowing, DAS). No irrigation was applied.

Table 1. - Sources of tritordeum (HT), parental lines of H. chilense (H) and wheat (T) and wheat genotypes used in the experi­

ments.

T. turgidum conv. durum

T. aestivum sp. vulgare

sp. sphaerococcum

H. chilense

X Tritordeum

Line

T22 T24

cv. Ardente cv. Cajeme

cv. Mara T59 HI H7

HT18 HT22 HT24 HT8 HT9 HT5

HTCI

Ploidy level

4x 4x 4x 6x 6x 6x 2x 2x 8x 6x 6x 6x 6x 6x 6x

Sonrce

CIMMYT Prof. E. Sanchez-Monge,

Italy CIMMYT

Italy P.B.I. Cambridge, UK P.B.I. Cambridge, UK

USDA H7 x T59 HI x T22 HI X T24

HT22 x HT24 HT18 x HT22

SP.

Recombined tritordeum from HT22 x HT24 Secondary tritordeum from HT9 x HT8

Eur. J. Agron.

Agronomic evaluation of tritordeum

Measurements

Soil water content and evapotranspiration

Volumetric soil water content was measured in the 1987/88 experiment with a neutron moisture meter (Campbell Pacific, California, U.S.A.) calibrated pre­viously for the experimental site. One access tube was located in the centre of each plot and readings were taken at 30 em intervals to a depth of 2.4 m. The sur­face soil water content (0-15 em) near each access tube, was determined gravimetrically. Measurements of soil water content were made every 14 days through­out the growing season, commencing at sowing.

Crop evapotranspiration (ET) was estimated using a soil water balance procedure (Haise and Hagan, 1967) with a correction for deep percolation based on soil water measurements at the 210 and 240 em depths. Reference evapotranspiration (ETa) was calcu­lated by the FAG-modified Penman equation (Doorenbos and Pruitt, 1977).

Meteorological data were recorded at a weather sta­tion situated 5 km from the experimental site.

Plant measurements

Four plants per plot were dissected at weekly inter­vals in the second year and the development of the apex was scored using the stages defined in Kirby and Appleyard (1986). Thermal time (accumulated temperature, base temperature 0 °C) was calculated as described in Weir et al. (1984). Physiological matu­rity was assessed as the total loss of green colour from the ears. Above-ground biomass was measured at tillering, stem elongation, ear emergence, anthesis and maturity.

Prior to maturity, the harvested area in the centre of each individual plot was 0.3 m2• Green plant parts (leaf, stem and ear) were separated and the projected green area determined using an LI-COR area meter (Model 3100, LI-COR, Inc., Lincoln, NE) enabling calculation of the green area index (GAl, m2 green area m-2). The number of tillers m-2 was recorded in the same samples. Dry weights were recorded after oven-drying plant samples at 70 oc for 48 h.

At maturity, 6 m2 (1.2 x 5 m) in the centre of each plot were harvested. All above-ground biomass at final harvest was weighed immediately after cutting and subsampled for moisture determination. The num­ber of ears m-2 was assessed from the total harvest per plot. Following threshing, the grain yield was cal­culated after determining the grain moisture content in a subsample. The 1000-grain weight was deter­mined from a subsample of the grain harvested from each plot. The number of grains per ear and number of grains per spikelet were determined from a sub­sample of 10 ears per plot. Harvest index (HI) was calculated as the ratio of grain yield to above-ground biomass at maturity on a dry matter basis.

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85

Water use efficiency based on dry biomass (WU~) was calculated as the ratio of the above-ground bio­mass at maturity to total ET. Water use efficiency based on grain yield (WUE_,) was calculated as the ratio of grain yield to total tT.

Statistical analysis

Analysis of variance was used to determine the sta­tistical significance of treatment effects. Differences between means were compared by Duncan's Multiple Range test at p < 0.05.

RESULTS

Meteorological conditions

Weekly meteorological data for the experimental period are presented in Figure I. Crops reached maturity between 162-186 days after sowing (DAS). Total rainfall from sowing to maturity was 333 mm in 1986/87 and 218 mm in 1987/88; reference evapo­transpiration values (ETa) for the equivalent periods were 515 mm in 1986/87 and 505 mm in 1987/88. Rainfall until anthesis (124 DAS) was 263 mm in 1986/87 and 179 mm in 1987/88, with an additional rainfall of 70 mm and 39 mm respectively between anthesis and maturity. ETa was relatively constant at 5.9 and 6.5 mm per week until approximately 45 DAS (tillering) in 1986/87 and 1987/88 ; thereafter it increased, reaching 46.2 and 49.3 mm per week at maturity. The increase in both temperature and evapo­transpiration, combined with the decrease in rainfall after anthesis, resulted in a post-anthesis water short­age to the crops in both years.

The meteorological conditions in both growing sea­sons were similar to the long-term average with the exception that the rainfall in May and June 1987 was considerably lower.

Phenology

In 1987/88, there were only small differences in the phenological development of both tritordeums, which were similar to that of the late wheat (Table 2). Both tritordeums and the late wheat reached anthesis between 121 and 126 DAS (1491 oc days and 1573 oc days), and grain maturity by 171 DAS (2440 oc days). The tritordeums and the late wheat developed more slowly than the early wheat (Table 2). Relative to the early wheat, the double­ridge stage was reached 6 and 14 days later, respec­tively, by the recombined and secondary tritordeums ; terminal spikelet formation occurred 20 days later in both tritordeums. Anthesis and maturity were reached 14 days and 9 days later in the tritordeums than in the early wheat. The duration of the post-anthesis period ranged from 45 days to 50 days for the four geno-

86

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Feb March April May June

60 80 100 120 140 160 180 200

Days after sowing

M. Gallardo and E. Fereres

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Figure 1. - Weekly maximum and minimum temperature, rainfall and reference evapotranspiration for the two experimental seasons at Cordoba: (a) 1986187, (b) 1987188.

types with the secondary tritordeum having the short­est duration. The phenological development of recom­bined tritordeum in relation to the early and late wheats were very similar (on a DAS basis), in both growing seasons.

Tillering pattern

For the recombined and secondary tritordeum, til­ler production was considerably higher than for late wheat (Figure 2). In 1986/87 the maximum tiller num­ber for the recombined tritordeum was 1320 tillers m-2

at 163 DAS compared with 800 tillers m-2 for the late wheat at 108 DAS (Figure 2a). In 1987/88 the maxi­mum tiller numbers for the recombined and the sec­ondary tritordeum were 850 and 920 tillers m-2

respectively, compared with 500 tillers m-2 for the late wheat ; for these three genotypes maximum tiller number occurred at 94 DAS (Figure 2b).

In 1986/87 all genotypes produced more tillers than in 1987/88 (Figure 2). The larger plant popula­tion, the earlier sowing date and the higher rainfall during the growing season in 1986/87 are likely con­tributing factors.

Table 2. - Days after sowing for the double ridge, terminal spikelet, anthesis and maturity stages. Thermal time (°C days) is given in parentheses. Data from the 1987/88 experiment.

Genotype Double Terminal Anthesis Maturity ridge spikelet

Recombined tritordeum 56 (585) 84 (907) 123 (1528) 171 (2440) Secondary tritordeum 64 (686) 84 (907) 126 (1573) 171 (2440) Late wheat 64 (686) 84 (907) 121 (1491) 171 (2440) Early wheat 50 (517) 64 (686) 112 (1316) 162 (2235)

Eur. J. Agron.

Agronomic evaluation of tritordeum

1600 r----,.----,.-----.------,

1400

1200

~E 1000

~ 800

i= 600

400

200

•-• Recombined tritordeum I I ·-·~...... ~

(a)

0~----~----~----~----~ 0 50 100 150 200

Days after sowing

87

7

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E 6 c-o Secondary tritordeum

(b)

N .t.-.. Early wheat

.s 5 X Q) 4 "0 c al 3 Q) ..... al c 2 Q) Q) .....

C)

200 Days after sowing

Figure 2.- Seasonal production of tillers m-2 over the two growing seasons: (a) 1986!87, (b) 1987/88. Arrows indicate 50 per cent anthesis ; vertical bars are the standard errors.

The duration of tiller production for recombined and secondary tritordeum was considerably longer than that for the wheats (Table 3). Between 64-94 DAS, faster rates of tiller production occurred in both tritordeums than in the wheats. Approximately 47 per cent of the total tillers of the two tritordeums were produced in this period. In contrast, 89 and 99 per cent of the total tillers of the late and early wheats were produced before 63 DAS.

The rate of tiller senescence in the secondary tri­tordeum was over four times faster than that found in the late wheat (Table 3). A greater proportion of the tillers produced by the tritordeums was infertile ; the ratio of fertile to maximum tiller number being 0.73 and 0.67 for late and early wheat, and only 0.56 and 0.49 for recombined and secondary tritordeum.

Biomass accumulation and green area index

The patterns of biomass accumulation and green area index (GAl) for the 1987/88 experiment are pre-

sented in Figure 3. There were only small differences in the rate of accumulation of biomass between the tritordeums and late wheat until anthesis (120 DAS) (Figure 3a). Thereafter, recombined tritordeum accu­mulated biomass more slowly, reaching a maximum of 900 g m-2 (Figure 3a). Secondary tritordeum and late wheat continued to accumulate biomass at simi­lar rates with both reaching a maximum of 1300 g m-2

at 154 DAS (Figure 3a). Early wheat accumulated bio­mass more rapidly than the other genotypes, reaching a maximum biomass of 1400 g m-2 at 143 DAS, 11 days earlier than secondary tritordeum (Figure 3a).

In all genotypes, maximum GAl occurred close to anthesis (Figure 3b). There were no statistically sig­nificant differences in GAl between both tritordeums and late wheat, although recombined tritordeum had a lower biomass accumulation. Maximum GAl for these genotypes was 4.0, 4.2 and 3.5 m2 m-2 at 119 DAS. Early wheat had a relatively higher GAl until 112 DAS, reaching a maximum of 4.8 m2 m-2 at 94 DAS ; thereafter GAl declined more rapidly than

Table 3. - Rate of tiller production for the 0-63 and 64-94 DAS periods, rate of tiller senescence (94-1 54 DAS) and the ratio of fertile to maximum number of tillers produced. Data from the 1987188 experiment.

Genotype

Recombined tritordeum Secondary tritordeum Late wheat Early wheat

Vol. 2, ll0 2- 1993

Rate of tiller production (tillers m-2/day-)

0-63 DAS 64-94 DAS

7.9 7.7 7.2

10.8

11.5 14.0

1.7 0.1

Rate of tiller senescence

(tillers m-2/day-)

95-154 DAS

2.8 4.9 1.2 2.1

Fertile/ total tillers

0.56 0.49 0.73 0.67

88 M. Gallardo and E. Fereres

2000 7

•-• Recombined trftordeum (a) - •-• Primary tritordeum

(b) ~ 6

1600 o-o Secondary tritordeum E o-o Secondary tritordeum

- •-• Early wheat "' ~ ~'>-~'> Late wheat 10 .· .s 5 E -9 1200

X Q) 4 "0

U) .£ U) as ~y·-· as 3 E 800 Q) ..... 0 as co c 2

400 #' Q) Q) .....

.,. C)

0 0 50 100 150 200 50 100 150 200

Days after sowing Days after sowing

Figure 3. - Biomass accumulation (a) and green area index (b) as a function of days after sowing in 1987188. Arrows indicate

50 per cent anthesis ; vertical bars are the standard errors of the means (all data).

for the other genotypes. Similar patterns and relative differences for comparable cultivars were recorded in 1986/87. Biomass and GAl were higher in 1986/87, presumably because of the higher tiller production.

Yield and yield components

In 1986/87 above-ground biomass at maturity, grain yield and harvest index were considerably lower for recombined tritordeum than for late and early wheat (Table 4a). Final biomass and grain yield of recom­bined tritordeum were respectively 28 and 59 per cent lower than for late wheat, and 26 and 66 per cent lower than for early wheat. In 1987/88 there were similar relative differences between recombined tritor­deum and the wheats (Table 4b). In contrast, the sec­ondary tritordeum had a final biomass close to that of the wheats (Table 4b). However, grain yield was

appreciably lower, being only 59 per cent of that of the late wheat. Compared to recombined tritordeum, secondary tritordeum had a larger biomass and grain yield, being 45 and 158 per cent higher respectively, and the additional breeding had improved the harvest index from 0.14 to 0.24.

The number of grains per ear and mean grain weight were considerably lower in recombined tritor­deum than in the wheats in 1987/88 (Table 5). The secondary tritordeum produced a number of grains per ear similar to that of the wheats, whereas that of the recombined tritordeum was approximately three times smaller (Table 5). The mean grain weight of both tri­tordeums was almost identical, being approximately 53 per cent that of the late wheat. Similar differences between the recombined tritordeum and the early and late wheats were recorded in 1986/87 (data not pre­sented).

Table 4. -Above-ground biomass at maturity, grain yield and harvest index.

(a) 1986/87

Genotype Biomass Grain yield Harvest index

(g m-') (g m-')

Recombined tritordeum 820 145 0.18

Late wheat 1134 354 0.31

Early wheat 1109 431 0.39

l.s.d. (p < 0.05) 228 42 0.03

(b) 1987/88

Genotype Biomass Grain yield Harvest index

(g m-2) (g m-')

Recombined tritordeum 905 124 0.14

Secondary tritordeum 1316 321 0.24

Late wheat 1312 540 0.41

Early wheat 1237 562 0.46

l.s.d. (p < 0.05) 195 89 0.04

Eur. J. Agron.

Agronomic evaluation of tritordeum

Table 5. - Grain yield components in the 1987188 experiment.

Genotype Ear number (m-2 )

Recombined tritordeum 474 Secondary tritordeum 451 Late wheat 370 Early wheat 456 l.s.d. (p < 0.05) 74

Water use efficiency

The wheat cultivars and the secondary tritordeum all had about the same seasonal biomass water use efficiency, WUEb (Table 6). However, recombined tri­tordeum had a significantly lower WUEb than the other genotypes. ET of all genotypes was similar, despite recombined tritordeum, having a much smaller above-ground biomass.

Pre-anthesis water use was greater in the tritor­deums and the late wheat than in the early wheat (Table 6). The ratio of ET pre-anthesis to ET post­anthesis was 2.1 for late wheat, 1. 7 for the tritor­deums and 1.3 for early wheat.

When water use efficiency was expressed in terms of grain yield (WUEY)' the differences between tritor­deums and wheats were magnified (Table 6). The two wheats had similar WUEY of approximately 1.4 g m-2 mm-1

, while secondary tritordeum had a value of about 0.8 g m-2 mm-1 and recombined tritor­deum 0.3 g m-2 mm-1•

DISCUSSION

The results indicate that tritordeum has suitable agronomic characteristics to be developed as a cereal crop in the mediterranean conditions of south-western Spain. In terms of dry matter production, phenologi­cal development and water use, secondary tritordeum was similar to the late wheat traditionally grown in

89

Spikelets Grains 1000 grain per ear per ear weight (g)

22.4 9.1 28.3 24.8 25.1 28.2 21.3 28.2 52.7 19.6 27.5 44.7

1.1 4.7 2.4

the area. Despite these similarities, the secondary tri­tordeum had a considerably smaller grain yield, its harvest index being only 0.24 compared to 0.41 for the late wheat. Considering the small amount of con­ventional breeding, which resulted in this substantial increase in harvest index from the recombined to the secondary tritordeum (A. Martin, personal communi­cation), the potential for further improvement may be considerable.

The relative inability of secondary tritordeum to produce grain was primarily due to two factors : (a) a much larger proportion of unproductive tillers, and (b) a lower mean grain weight. The larger proportion of unproductive tillers result from the very high rate of tiller production late in the season, and the subse­quent much higher rate of tiller senescence. The late wheat produced 89 per cent of its tillers prior to 63 DAS, compared to 47 per cent, for the secondary tritordeum.

The late developing tillers of the secondary tritor­deum did not produce ears. Tillers of winter cereals appearing late in the season generally have insuffi­cient time to complete their development ; they also compete for assimilate with earlier tillers without con­tributing to final yield (Gallagher et al. 1976). The excessive late tillering of tritordeum is probably attributable to the partial inheritance of the perennial growth habit from the parent species Hordeum chi­tense.

Table 6. - Seasonal evapotranspiration (ET), ET pre-anthesis, ET post-anthesis, water use efficiency based on dry matter (WUEb)

and water use efficiency based on grain yield (WUEY) in /987188.

Genotype ET ET pre- ET post- WUEb WUEY (mm) an thesis anthesis (g m-2 mm-') (g m-2 mm- 1)

Recombined tritordeum 385.5 239.0 148.3 2.34 0.32 Secondary tritordeum 387.3 245.3 142.3 3.40 0.83 Late wheat 395.8 266.5 129.3 3.32 1.37 Early wheat 380.3 214.1 166.2 3.25 1.48 l.s.d. 15.1 16.6 19.4 0.50 0.23 (p < 0.05)

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90

A comparative analysis of yield components between secondary tritordeum and late wheat showed that despite producing more ears per m2

, more spike­lets per m2 and a similar number of grains per ear, the much smaller mean grain weight of secondary tri­tordeum was a major contributing factor to the smaller grain yield. The continued genetic influence of the very small grain size of H. chilense (3-4 g per 1000 grains) and the considerable amount of assimi­lates required to synthesise the high protein content in tritordeum (Penning de Vries et al., 1983) could be explanations for the smaller grain size.

Biomass accumulation in recombined tritordeum was 31 per cent less than in secondary tritordeum, with most of the difference occurring after anthesis. Genotypic differences in biomass production depend on differences in green area index or intercepted radi­ation (Monteith, 1977). However, the GAl's of recombined and secondary tritordeum were similar throughout the growing season. The difference in post-anthesis dry matter production between recom­bined tritordeum and secondary tritordeum may have resulted from the low harvest index of recombined tritordeum acting as a sink limitation.

Grain yield in secondary tritordeum was 61 per cent more than in recombined tritordeum, the respective harvest indices (HI) being 0.24 and 0.14. The improvement in HI resulted from the large increase in floret fertility, from 0.4 to 1.0 grain per spikelet. However, the mean grain weight was not modified through selection for high yield in tritordeum. This is consistent with the improvement in grain yield in wheat from old to modern cultivars which largely resulted from more grains per ear or grains m-2, mean grain weights having remained relatively constant (Fischer, 1983).

Both tritordeums had the same seasonal evapotran­spiration (ET) as the two wheats. The seasonal distri­bution of ET for the tritordeums was intermediate between the two wheats. The earlier flowering date of the early wheat was responsible for a larger propor­tion of ET occurring after anthesis. Secondary tritor­deum had the same WUEb as both wheats, while recombined tritordeum had a significantly lower WUEb. This difference was due to the smaller bio­mass production of the recombined tritordeum.

The similarities between the secondary tritordeum and the late wheat in biomass production, phenologi­cal development and water use indicated the potential of tritordeum for crop production under mediterranean conditions. Suggested breeding strategies to further adapt tritordeum to these conditions are (i) reduced duration of tillering, (ii) increased grain size and (iii) earlier flowering. This latter strategy has been employed successfully to increase cereal production under post-anthesis drought conditions (Turner and Begg, 1981 ; Passioura, 1986). Earlier development results in a larger proportion of seasonal ET occurring

M. Gallardo and E. Fereres

after anthesis. Passioura (1977) reported a correlation between the proportion of post-anthesis ET and grain yield in crops experiencing water shortage during the reproductive phase. To exploit this strategy, early vig­our i.e. higher rates of growth early in the season when temperatures are low, is required. Considering that secondary tritordeum had the lowest GAl in the vegetative phase (0-63 DAS) (Figure 3b), it is likely that rapid genetic advance could be obtained by selecting for early vigour among the population of secondary tritordeum.

A comparative analysis of the development of tri­tordeum and triticale shows that similar breeding problems were encountered and the same morpho­physiological traits were found to be improved in the early stage of both breeding programs. Yield has increased faster in tritordeum than in triticale as a consequence of the technologies recently emerged ; after only 10 years of plant breeding some of the sec­ondary lines of tritordeum approach 80 per cent of wheat yield in our field conditions (Martfn, 1988).

Although secondary tritordeum was only assessed in one season, the consistency of (i) the behaviour of the recombined tritordeum and (ii) the differences between recombined tritordeum and the two wheats in both growing seasons, suggest that the observed per­formance of the secondary tritordeum was representa­tive. The substantial improvement from the recom­bined tritordeum to secondary tritordeum in biomass accumulation and harvest index, achieved by mass selection in several generations, suggests that further improvements could be made. Tritordeum's high grain protein content, good adaptability to mediterranean conditions and agronomic performance which already approaches high-yielding wheat varieties, demonstrates the considerable potential of this recently synthetised cereal.

ACKNOWLEDGMENTS

We thank Dr. A. Martin and Mr. J. Ballesteros for providing the seeds of tritordeum and for valuable discussions. The helpful comments on the text by Drs. R. B. Thompson, N.C. Turner and J. Palta are gratefully acknowledged.

REFERENCES

Cubero J. I., Martin A., Millan T., Gomez-Cabrera A. and de Haro A. (1986). Tritordeum: A new alloploid of potential importance as a protein source crop. Crop Sci., 26, 1186-1190.

Doorenbos J. and Pruitt W. 0. (1977). Crop water requirements. Irrigation and drainage. Paper No. 24. FAO, Rome, Italy, p. 143.

Eur. J. Agron.

Agronomic evaluation of tritordeum

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