The Eleventh Regional Wheat Workshop For Eastern ... - Cimmyt

Response ofbread wheat genotypes to drought simulation - Kimurto et al.
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RESULTS
The mean ANOVA (Table I) showed that there was significant difference (p==O.Ol) between
watering regimes and among genotypes tested for grain yield. The control treatment had the
highest yield for all genotypes in both seasons while the terminally stressed treatment (70
mm) had the lowest yield (Table 2). In both seasons, the treatments where the lowest quantity
of water were applied had the lowest number of seeds per head, number of tillers per plant,
percent reproductive tillers, spike lets per head and kernel weight, while treatments where
more moisture was applied recorded higher values (Table 2). The most stressed conditions
also recorded the highest number of sterile florets per head and the plants with shortest ears.
Generally, yield and yield components decreased with increasing moisture stress. Genotype
R748 had the highest mean grain yield followed by Duma, while R830 and R831 were the
lowest yielders (Table 3). Genotype R833 had the highest number of seeds per head in both
seasons followed by R748 and Duma while R830 attained the lowest overall number of seeds
per head (Table 3). Genotype R831 had the longest ears and second highest number of
spikelets per head after R833 and highest number of sterile florets per head. R748 had the
lowest number of sterile florets per head and highest seed weight followed by Duma. R833
had the lowest seed weight and shortest ears followed by R830 in both seasons (Table 3).
R830 and R748 headed and matured last while Duma and R833 were' the earliest maturing
genotypes. R748 were the longest plants while R833 and Duma were the shortest (Table 3).
Genotype R831 and R830 produced the highest number of tillers per plant but recorded the
lowest number of reproductive tillers while R833 and R748 produced the lowest tiller number
but number of highest reproductive tillers.
DISCUSSION
Severe water stress from seedling stage to maturity reduced expression of all yield
components. Terminal and early drought reduced grain yield by 62.2% and 52.7% as
compared to 44.3% and 21.4% loss by mid and late drought when compared to control. These
show that reproductive stage was the most critical stage that required moisture followed by
seedling stage. Duma and R748 suffered highest yield loss under mid to late season drought
while R830, R833 and R831 were affected more by early drought, showing that there was
genotypic differences in response to drought stress.
Highest yield loss during reproductive stages was associated with reduced number of seeds
per head (20.3%), increased number of sterile florets per head (28.3%), reduced number of
reproductive tillers (13%), reduced length of ears and number of spikelets per head (16.9%
and 14.3%, respectively) and reduced kernel weights (22.4%) for all genotypes (derived from
Table 2). Kernel weight was affected more by moisture stress from grain filling to maturity.
Soil moisture deficits could have hastened the ear emergence period, flowering and
pollination which consequently resulted in poor or incomplete pollination and poor seed set.
Moisture stress from grain filling to maturity was strongly associated with reduced number of
seeds per head (11.8%) and kernel weights (14.7%) which could have been caused by
shortened grain filling periods and reduced carbohydrate supply. There was increased kernel
abortions under these conditions. Highest reduction in ear length and spike lets per head
occurred under mid-late season drought because soil moisture deficits could have affected
spike vegetative development. Genotype R831 and R830 had the highest number of tillers per
plant but lowest number of reproductive tillers because of tiller abortions. Abortive tillers
contributed to low yield in these genotypes because they compete with main culm for
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