Abstract Six sets of 48 maize ( Zea mays L.) inbred lines, and their 96 single crosses generated using the North Carolina Mating Design II system, were evaluated for resistance to gray leaf spot (GLS). The aim of the study was to assess the implications of combining ability, heterotic effects, and potence ratio in breeding for GLS resistance in maize. Inbred lines, crosses, and two local commercial checks were artificially inoculated with Cercospora zeina and evaluated across nine field environments in Western Kenya from 2012 to 2014. Analysis of variance revealed significant ( p ≤ 0.05) differences in disease resistance among inbred lines and their single crosses. Both general combining ability (GCA) and specific combining ability (SCA) effects were significant ( p ≤ 0.05), suggesting that resistance was influenced by both additive and non‐additive genetic factors. However, the sums of squares of GCA were two to four times larger than those of SCA, indicating a greater role of additive genetic effects, although the magnitude varied depending on the genetic set under investigation. Further, there was a strong and significant correlation ( p ≤ 0.05) between the GCA effects of the parental lines and the resistance levels of their hybrid crosses, indicating GCA effects were predictive of hybrid resistance and that reciprocal recurrent selection may be a potential strategy of breeding for GLS resistance. Inbred lines CML202, CML210, and CML373 were the strongest general combiners. The highest SCA effects were observed in crosses such as CML373 × CML168, CML371 × CML168, and CML219 × CML205. Crosses derived from parents within compatible heterotic patterns exhibited significant ( p ≤ 0.05) mid‐parent heterosis, with the cross CML219 × CML123 showing the most pronounced heterotic effect. Other crosses with notable mid‐parent heterosis included CML371 × CML390, CML204 × CML160, and CML394 × CML168. Although the variation in potence ratio estimates indicated that the interactions between loci ranged from complementary to inhibitory epistasis, the most prevalent genetic interaction was overdominance. These findings suggest that breeding strategies to improve GLS resistance in maize should be adapted to the specific genetic backgrounds of parental material. While reciprocal recurrent selection would suit most of the evaluated genotypes, half‐sib and genomic selection could be the most effective in different contexts.
Nyanapah et al. (Thu,) studied this question.