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Fifteen experiments testing seven sets of genotypes under irrigated
non-stress and drought stress situations were conducted from 2004 to 2006
with the objective to study the effect of different severity levels of
drought on tolerant and susceptible advanced breeding lines, current
varieties, and traditional and improved donors, and to study the effect of
selection for high early vigor on yield. With the onset of drought, a yield
reduction due to a decrease in biomass was observed in both susceptible and
tolerant lines. However, after an initial reduction in yield, tolerant
lines were able to sustain a yield loss more effectively than susceptible
lines by better maintenance of biomass and higher harvest index. Under
intermittent drought stress, genotypes with the ability to maintain higher
biomass, reflected in terms of high early vigor recorded 3wk after
transplanting, recorded higher grain yield than genotypes with low early
vigor. Lines with high early vigor yielded higher under both irrigated
non-stress and intermittent drought stress situations. Under intermittent
stress, plants with high vigor, low vigor, or random plants with high or
low vigor coming from tolerantxsusceptible crosses yielded higher than did
the plants with the same vigor coming from susceptiblexsusceptible crosses.
Under both irrigated non-stress and intermittent drought stress situations,
early vigor showed significant genetic correlation with grain yield and
could be included as an efficient selection criterion to improve yield in
the lowlands.
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