HYBRID PERFORMANCE OF SORGHUM AND ITS RELATIONSHIP TO MORPHOLOGICAL AND PHYSIOLOGICAL TRAITS UNDER VARIABLE DROUGHT STRESS IN KENYA

Sorghum, Sorghum bicolor L. Moench, is grown mostly in semi-arid clima tes where unpredictable drought stress constitutes a major production constraint. To investigate hybrid performance at different levels of d rought stress, 12 single-cross hybrids of grain sorghum and their 24 p arent lines were grown in eight site-season combinations in a semiarid area of Kenya. In addition, a subset of 20 genotypes was evaluated at the seedling stage under polyethylene glycol (PEG)-induced drought st ress. Environmental means for grain yield ranged from 47 to 584 g/m(2) reflecting the following situations: two non-stress, one moderate pre flowering, four moderate terminal and one extreme drought stress. Mean hybrid superiority over mid-parent values was 54% for grain yield and 35% for above-ground biomass. Across environments, hybrids out-yielde d two local varieties by 12%. Differences in yield potential contribut ed to grain yield differences in all stress environments. Early anthes is was most important for specific adaptation to extreme drought. Fiel d performance was not related to growth reduction and osmotic adjustme nt under PEG-induced drought stress. In conclusion, exploitation of hy brid vigour could improve the productivity of sorghum in semi-arid are as.