Evaluation of Grain Yield and Its Components in Wheat Genotypes under Terminal Drought Stress Conditions in Darab Region

Nine bread wheat and one durum wheat genotypes were evaluated under non-stress, mild and severe terminal drought stresses conditions at Darab Agricultural Research Station in three cropping seasons (1998-2001). Split plot arrangements in randomized complete block design with there replications was used. Main plots included: three moisture regimes (1. non stress, 2. mild drought stress: 25% reduction of water requirement from 50% anthesis of local check cultivar (Chamran) and 3. severe drought stress: 50% reduction of water requirement from 50% anthesis of local check cultivar (Chamran). Ten wheat genotypes were randomized in sub-plots. Results indicated that mild and severe drought stresses significantly (P < 0.05) decreased grain yield for all genotypes. Main reason for grain yield reduction in mild drought stress (21.8%) and severe drought stress (40.7%) was reduction in grain number per spike and thousand grain weight, respectively. Genotype no. 6 produced the highest grain yield (5352 kg ha-1) in non-stress conditions. The highest grain yield in mild drought stress (4178 kg ha-1) and severe drought stress (3505 kg ha-1) conditions was obtained from genotype no. 9. Stress tolerance index (STI), geometric mean productivity (GMP) and mean productivity (MP) showed the highest correlation with the grain yield in non-stress, mild and severe drought stresses conditions. Therefore, these indices are suggested for selection for drought tolerant genotypes. According to these indices, genotypes no. 6 and 9 were the most tolerant genotypes under mild and severe drought stresses, respectively. Correlation analysis showed that biological yield and harvest index had significant and positive correlations with grain yield in all three moisture regimes. Therefore, genotypes no. 6 and no. 9 are suggested to be used in wheat breeding programs for improving terminal drought tolerance.