QTL MAPPING IN TROPICAL MAIZE .1. GENOMIC REGIONS AFFECTING LEAF FEEDING RESISTANCE TO SUGARCANE BORER AND OTHER TRAITS

Sugarcane borer (SCB), Diatraea saccharalis Fabricius, is a serious pe st in tropical maize production areas in the Americas. Little is known about the genetic resistance of maize genotypes to this pest. In this study, we mapped and characterized quantitative trait loci (QTL) affe cting resistance to the leaf feeding generation of SCB (1SCB), grain y ield under both protection (GYP) and infestation (GYI) with SCB larvae , and plant height (PHT). A total of 171 F-2 genotypes derived from cr oss CML131 (susceptible) x CML67 (resistant) and 93 RFLP marker loci w ere used in QTL analyses. F-3 lines were evaluated for the above trait s and grain yield reduction (GYR) in field experiments with two replic ations at two or three tropical environments. Resistance was assessed by rating leaf feeding damage after artificial infestation with SCB la rvae. The method of composite interval mapping with selected markers a s cofactors was used for detection and characterization of QTL. Resist ance to 1SCB was significantly affected by 10 putative QTL on Chromoso mes 1, 2, 5, 7, 8, 9, and 10. These showed predominantly additive gene action and explained 65.0% of the phenotypic variance and 93.5% of th e genetic variance in a simultaneous Bt. Six QTL for GYP, Eve QTL for GYI with primarily dominant genetic effects, and Pour QTL for PHT with primarily additive genetic effects were identified, explaining in tot al about one third of the phenotypic variance for the respective trait . No more than one putative QTL was found to be common between differe nt characters. QTL x environment interaction was found to be significa nt for 1SCB ratings only. Based on these data, prospects for improving 1SCB resistance by marker-assisted breeding are promising.