Yield and yield stability of four population types of grain sorghum in a semi-arid area of Kenya
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Sorghum [Sorghum bicolor (L.) Moench] is widely grown in semi-arid tropics where local farmers depend on the adaptability of their rainfed crops to unpredictable drought and other stress factors. To investigate the effects of heterozygosity and heterogeneity on the adaptability of grain sorghum, two sets of material, each containing 12 parent lines, six single-cross hybrids, six two-component blends of parent lines, and six two-component hybrid blends were grown in eight macro-environments in the semi-arid Makueni District of Kenya, during 1991 through 1993. Environmental means for grain yield ranged from 584 to 47 g m−2 In all environments, hybrids outyielded their parent lines, with a mean relative hybrid superiority of 54%. Blending effects were non-significant. Combined analyses of variance were computed with logarithmically transformed data. Entry × environment interaction effects were more important than genetic effects. Lines in pure stand contributed most to the total entry × environment interaction variance. Wide ranges were found within all four groups for stability parameters derived from regression analysis. On average, hybrids in pure stand had most favorable values. Pattern analysis (classification and ordination techniques) was applied to the environment-standardized matrix of entry means from the individual environments. A one-way classification clearly distinguished homozygous from heterozygous entries. Heterogeneous entries were not consistently grouped together. Performance plots for different entry groups showed various patterns of adaptation and illustrated the superiority of heterozygous entries. The biplot from ordination underlined the importance of entry × type-of-drought-stress interaction. Principal Components 1 and 2 were highly correlated with entries' mean yield and regression coefficient, respectively. Breeding heterozygous cultivars could contribute to increased grain yields and improved yielding stability of sorghum in the target area of Kenya.