Combining Ability And Heterotic Groups Of Earlymaturing White Maize (Zea Mays L.) Inbreds Under Strigainfested And Striga-Free Environments

ABSTRACT Striga hermonthica constitutes a major constraint to maize production and productivity. It is the largest single biological constraint to food production in Sub-Saharan Africa. Hence there is the need to develop hybrids that are tolerant to this constraint. Knowledge and understanding of Striga resistance in early maturing maize inbreds are crucial for the developments of hybrids adapted to Striga-infested environments in the sub-region as well as for enhancing breeding strategies. This study examined the performance of 15 early maturing inbreds and their F1 progenies derived from a 15 x 15 diallel mating design under Striga-infested and Striga-free environments; estimated general and specific combining ability effects for grain yield and other related traits and classified the inbred lines into heterotic groups. The inbred lines were evaluated using the randomized complete block design while a 10 x 11 lattice was used in the evaluation of the hybrids. The evaluations were conducted at three locations in 2015 in Nigeria. Grain yield, plant height, days to silking and anthesis, ear height, root lodging, ear aspect, plant aspect, Striga damage at 8 and 10 weeks after planting and number of emerged Striga plants at 8 and 10 weeks after planting were the traits measured. Data were subjected to analysis of variance and correlation analysis using PROC GLM in SAS while the grain yield was subjected to GGE biplot analysis to determine the stability of the genotypes. General combining ability (GCA) and specific combining ability (SCA) mean squares were significant for grain yield and other agronomic traits under Striga-infestation and across research environments indicating that both additive and non-additive gene effects were important in the inheritance of grain yield under the two contrasting environments. The larger proportion of GCA sum of squares over SCA for grain yield under Striga-infested, Striga-free and across research environments indicated the predominance of additive over non-additive genetic effects for grain iii yield and that GCA was the major component accounting for the differences in grain yield among the hybrids. The inbreds TZEI 56 and TZEI 383 were the highest yielding inbreds across the research environments, whilst TZEI 7 and TZEI 326 were the most stable. The hybrid TZdEI 352 x TZEI 355 was the highest yielding across research environments based on the IITA selection index. The GGE biplot analysis identified the hybrids TZdEI 352 x TZEI 355, TZEI 296 x TZdEI 352 and TZEI 7 x TZdEI 352 as high yielding and stable across research environments. These should be extensively tested and promoted for commercialization to contribute to improved maize production and productivity in SSA. Inbreds TZEI 7 and TZdEI 352 were identified as the best testers based on display of highly significant and positive GCA effects, classification into specific heterotic groups and grain yield performance. These inbred lines may be used to classify other early maturing white maize inbred lines into heterotic groups and also to identify superior hybrid combinations