The European corn borer (Ostrinia nubilalis Hübner) 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 corn 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 IS, IL, 2S, 2L, 3L, 7L and IOL, 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.

One 10‐inbred‐line diallel of maize (Zea mays L.) was evaluated for 2 years for resistance to second‐brood European corn borer [Ostrinia nubilalis (Hübner)], and a second 10‐line diallel was evaluated for 1 year for resistance to first and second broods. First‐brood evaluations were based on leaf‐feeding ratings in the pretassel stage, and second‐brood evaluations were based on plant‐cavity counts in mature plants. Variations attributed to general combining ability and general combining ability ✕ years were highly significant in the first diallel, but none of the F‐tests for specific combining ability were significant. Different levels of borer infestation in the 2 years probably affected the estimates of genetic effects. In the second diallel, variations attributed to general combining ability and specific combining ability were highly significant for both first‐ and second‐brood data. Also, heterosis was highly significant, with resistance being partially dominant. Inbred B52 contributed the most resistance to second brood, and CI31A and B49 contributed the most resistance to first brood. There are differences in the genes of the maize plant that condition resistance to first and second broods, but some genes may contribute resistance to both broods.

The European corn borer (ECB) [Ostrinia nubilalis (Hübner)] is the most damaging corn (Zea mays L.) insect pest in the USA. Utilization of corn hybrids with reduced susceptibility to ECB is the most economical method of control. Iowa normally has two generations of ECB each season that coincide with two growth stages of the plant. Sources of resistance to both generations in one genotype are rare and additional sources are needed. Resistance to ECB is conditioned by several genes and is primarily additive in gene action. For these reasons, a 10‐line synthetic, designated BS9, was developed specifically to be used in a recurrent selection program. Four cycles of S1 recurrent selection were conducted for resistance to both first and second generation ECB, and these cycles were then evaluated to determine the extent to which resistance for the whole life of the plant could be improved. The four cycles of selection decreased ratings in BS9 from 3.6 to 2.7 for first generation ECB damage and from 6.4 to 4.4 for second generation ECB damage on a 1 to 9 scale, and cavity counts (one cavity = 2.5 cm) decreased from 8.9 to 3.1. High artificial infestations of first, second, and both generations of ECB resulted in average grain yield reductions of 5.7, 22.0, and 21.1%, respectively. An increase in resistance in advanced cycles of BS9 decreased yield reductions caused by artificial infestations of ECB. Yielding ability also decreased, however, resulting in no yield advantage of the more resistant material under high infestation levels. Yield reductions were not different between testcrosses of testers that varied in ECB resistance, which resulted in nonsignificant correlations between ECB damage ratings and yield. Tolerance may be the key factor in this response.