QTL mapping in tropical maize .2. Comparison of genomic regions for resistance to Diatraea spp.

Southwestern corn borer (SWCB), Diatraea grandiosella (Dyar), and the sugar cane borer (SCB), Diatraea saccharalis (Fabricius), are serious insect pests in maize (Zea mays I,.) production areas of Central America and the southern USA. We mapped and characterized quantitative trait loci (QTL) affecting resistance to the leaf feeding generation of SWCB (1SWCB), compared these QTL with those for resistance to the leaf feeding generation of SCB (1SCB) identified in the same mapping population, and assessed the consistency of QTL for 1SWCB across two populations. One hundred seventy-one F-2 genotypes from cross CML131 (susceptible) x CML67 (resistant) and 100 RFLP marker loci were used for the QTL analyses. 1SWCB and 1SCB resistance were assessed in F-2:3 lines by leaf damage ratings (LDR) after artificial infestation in field experiments with two replications at one subtropical environment in 2 yr. The method of composite interval mapping (CIM) was used for QTL detection. Estimates of genotypic (sigma(g)(2)) and genotype x year interaction variance (sigma(gy)(2)) were highly significant for 1SWCB LDR and 1SCB LDR. Phenotypic and genotypic correlations between both traits were 0.62 and 1.02, respectively. For 1SWCB LDR, six QTL were detected explaining 53.3% of <(sigma)over cap (2)(g)>, with two QTL displaying significant QTL x year interactions. Ten QTL were detected for 1SCB LDR, accounting for 98.2% of <(sigma)over cap (2)(g)>. The QTL showed predominantly additive or partially dominant gene action. Seven out of 10 QTL were pleiotropic to both Diatraea spp. Three genomic regions, on Chromosomes 5 and 9, were consistent with a second mapping population derived from cross Ki3 (susceptible) x CML139 (resistant), for which seven QTL for 1SWCB LDR were found. Marker-assisted 'gene stacking' is recommended for transferring pleiotropic QTL into susceptible germplasm and for pyramiding QTL from different sources of insect resistance.