A study was carried out to study the combining ability effects of diallel cross hybrids for grain yield, agronomic traits and reaction to grey leaf spot (GLS). Forty five experimental diallel cross hybrids made from ten quality protein maize (QPM) inbred lines with varying level of resistance to GLS were evaluated along with three checks at Bako and Jima Research Centers during 2014/2015 cropping season. Analysis of variance showed significant variation (P≤0.05) among genotypes and between environments. This depicted the existence of genetic variation among genotypes in all studied traits. Mean squares characterized by general and specific combining ability effects were significant for the most traits and this suggested that both additive and non-additive gene actions have the contribution in the expression of the traits. However, the ratio of General combining ability (GCA) to specific combining ability (SCA) sum of squares were greater than unity, this revealed that there was preponderance of additive gene action in the expression of all the traits under study. Among inbred lines studied P6 and P10 had a desirable GCA effects for grain yield whereas P1, P4 and P10 were the best general combiners for GLS resistance. Furthermore, P10 was identified as good general combiner for grain yield as well as GLS is therefore recommended to be used in breeding programs with a purpose of developing both high yielder as well as GLS disease resistant genotypes. Crosses, P2×P8 and P4×P6 showed the most desirable performances and SCA effects for grain yield. Grain yield showed positive correlation between ear per plant, plant and ear height, and ear position whereas negative correlation were observed with GLS, days to anthesis, days to silking, plant aspect and ear aspect traits. The information which is generated in this study could be helpful to develop high yielding maize varieties with good agronomic traits as well as GLS resistance.
Key words: Agronomic traits, diallel, general combining ability, gray leaf spot, quality protein maize, specific combining ability.
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