Combining ability and cultivar superiority of sorghum germplasm for grain yield across tropical low- and mid-altitude environments

Sorghum grain production in sub-Saharan Africa is constrained by the fact that farmers' choice of improved varieties is limited. Hybrid cultivars have been shown to be more productive for grain than pure line and landrace varieties hence their development can enhance productivity and food security. This study was, therefore, conducted to determine combining ability of 18 sorghum lines, the level of heterosis and cultivar superiority of experimental hybrids in tropical lowland and mid-altitude environments. Eight cytoplasmic male-sterile lines were crossed with 10 male-fertile lines in accordance with the North Carolina II mating scheme to generate 80 experimental hybrids. The hybrids, parents and two standard check varieties were evaluated in replicated row-column α-designs across six environments in Mozambique, South Africa and Zimbabwe. Cultivar superiority was assessed using the cultivar superiority index (Pi). Results indicated significant (P ≤ 0.05) differences among genotypes for both grain yield potential and secondary traits. Hybrids were predominant in the top 20 ranking for grain yield, and displayed up to 285% standard heterosis. Overall hybrid mean yield was significantly higher than that of parents and standard check varieties, which was attributed to high levels of average heterosis and standard heterosis, respectively. Grain yield data were positively and significantly correlated with head length and number of leaves plant−1, suggesting an improvement in grain yield potential as the number of leaves and head size increase. General combining ability (GCA) and specific combining ability (SCA) effects were significant (P ≤ 0.05) for all traits, implying that both additive and non-additive gene effects were important. Both GCA and SCA effects significantly interacted with site effects demonstrating the need for multi-location testing of potential cultivars. However, the top grain yielders were generally stable across environments. Parents ICSV700, ICSR165, S35, IMDP97, ICSA4, ICSA724, and ICSA26 with positive and significant GCA effects, which also revealed significant SCA effects in crosses for grain yield were identified as potential materials for inclusion in the hybrid breeding programme.