The breeding possibilities and genetic parameters of maize resistance to foliar diseases

The combining ability and genetic parameters of maize grown in two different environments of diseases pressure were estimated for partial resistance to northern leaf blight (Exserohilum turcium, NLB) and gray leaf spot (Cercospora spp., GLS). Nine inbred lines were crossed in a complete diallel mating scheme including reciprocals. Two experiments were carried out to test the hybrids using randomised complete blocks design with three replications during the growing season 2008/2009. The severities of NLB and GLS were assessed under natural infestation conditions. The first experiment was the lowest NLB and GLS pressure environment, whereas the second was the highest. Data was evaluated using individual and joint Griffing’s diallel analyses. General and specific combining abilities were significant (P < 0.10) for NLB and GLS resistance under both pressures. Although additive and nonadditive gene effects were significant, the additive gene effects were more important for resistance to the diseases. The lines 1 (P₈₃), 6 (P_30F) and 7 (P_st) had the most outstanding general combining ability for NLB resistance, and the line 3 (P₈₀) was outstanding for resistance to GLS. Based on both diseases resistance and grain yield, the synthetic composites 6 × 7 × 3 and (6 × 7) × 3 were recommended for intrapopulational breeding using recurrent selection. Three promising hybrid combinations (the 3 × 6, and 5 × 7 for resistance to NLB, and 3 × 9 for resistance to GLS) were recommended for interpopulational breeding. Resistance levels to NLB and GLS resistance were better discriminated under HP than LP conditions; however, promising lines were detected under both pressures.