QTL MAPPING IN TROPICAL MAIZE - III - GENOMIC REGIONS FOR RESISTANCE TO DIATRAEA SPP AND ASSOCIATED TRAITS IN 2 RIL POPULATIONS

The southwestern corn borer (SWCB, Diatraea grandiosella Dyar) and sug arcane borer (SCB, Diatraea saccharalis Fabricius) are two related ins ect species that cause serious damage in maize production in subtropic al and tropical regions of Central and Latin America. We analyzed quan titative trait loci (QTL) involved in resistance to the first generati on of both borer species in two recombinant inbred line (RIL) populati ons from crosses CML131(susceptible) X CML67 (resistant) and Ki3 (susc eptible) x CML139 (resistant). Resistance was evaluated as leaf feedin g damage (LFD) in replicated field trials across several environments under artificial infestation. Leaf protein concentration and leaf toug hness were evaluated in one environment as putative components of resi stance. The method of composite interval mapping was employed for QTL detection with RFLP linkage maps derived for each population of RIL. E stimates of the genotypic and genotype x environment interaction varia nces for SWCB LFD and SCB LFD were highly significant in both populati ons. Heritabilities ranged from 0.50 to 0.75. In Population CML131 x C ML67, nine and eight mostly identical QTL were found for SWCB LFD and SCB LFD, respectively, explaining about 52% of the phenotypic variance (<(sigma)over cap>(2)(p)) for each trait. In Population Ki3 x CML139, five QTL for SWCB LFD were detected, explaining 35.5% of <(sigma)over cap>(2)(p). Several of these QTL were found in regions containing QTL for leaf protein concentration or leaf toughness. A low number of QTL in common between the two RIL populations and between RIL and corresp onding populations of F-2:3 indicated that the detection of QTL depend ed highly on the germplasm and population type. Consequently, chances of successful application of marker-based selection (MBS) for corn bor er resistance are reduced when QTL are not identified in the germplasm in which the final selection will be carried out.