MAPPING AND CHARACTERIZATION OF QUANTITATIVE TRAIT LOCI AFFECTING RESISTANCE AGAINST 2ND-GENERATION EUROPEAN CORN-BORER IN MAIZE WITH THE AID OF RFLPS

The European corn borer (Ostrinia nubilalis Hubner) is an important pest in the global production of maize (Zea mays L.). In this study, we mapped and characterized quantitative trait loci (QTLs) significantly affecting resistance against second-generation European com borer (2ECB) and plant height with the aid of RFLP markers. A total of 300 F3 lines derived from cross B73 (susceptible) x B52 (resistant) were assayed for their parental F2 genotype at 87 RFLP loci. Field data on plant height and resistance against 2ECB were collected for the 300 F3 lines, the parents and the F2 generation at two sites, Ames and Ankeny, IA, USA. Resistance was assessed by measuring the damage of stalk tissue (tunnel length) caused by severe artificial infestation with 2ECB larvae. Genotypic variances among F3 lines were highly significant for tunnel length and plant height, but genotype by location interactions were significantly different from zero only for plant height. Heritabilities were intermediate (0.63) for tunnel length but high (0.87) for plant height. The genotypic correlation between the two traits was 0.29. The method of interval mapping was used for localization of QTLs and estimation of their genetic effects. In the combined analysis across locations, genomic regions significantly affecting resistance against 2ECB were found on chromosome arms 1S, 1L, 2S, 2L, 3L, 7L and 10L. Genomic regions on IS, 3L and 9L significantly affected plant height. Results were largely consistent across locations. Different types of gene action were found for the putative QTLs for both traits. For tunnel length a total of 38 per cent of the phenotypic variance was explained by simultaneous mapping of the seven putative QTLs. The three putative QTLs for plant height explained 63 per cent of the phenotypic variance. On 3L, evidence was found for an interaction of genes conferring resistance to 2ECB and plant height. Significant digenic epistasis was detected for one pair of marker loci.