Exserohilum turcicum is a major constraint to maize production in the humid highlands of sub-Saharan Africa. To develop efficient cultivars, the gene action involved and genetic stability across target ecologies must be understood. A half diallel study of 12 inbred lines was conducted to assess the types of gene action involved in turcicum resistance and genetic stability across 5 locations in central and western Kenya. Both additive and non-additive gene effects were important and highly dependent on test ecologies. General combining ability accounted for 84% of the variation across locations and hence selection for resistance to turcicum should be effective if directed at disease environments. Dominant effects were less influenced by the environments, suggesting stability of turcicum resistance among hybrids. Two environments, Bukura and Kitale, were found most discriminating for the disease both among parental genotypes and among the F1 crosses. Half of lines used in this study were found to have acceptable levels of resistance. One parent, P2 (S4 80-17-2-1) had the most desirable qualities of per se resistance, general combining ability and genetic stability. Multi-locational breeding nurseries can be a useful strategy to identify turcicum resistant lines with wide ecological appeal to plant breeders.
Key words: Gene action, turcicum blight, resistance, genetic stability, genotype-by-environment interaction
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