Direct response of a maize synthetic to recurrent selection for resistance to stem borers

Selection against pink stem borer (Sesamia non-agrioides Lef) (PSB) attack was performed in the maize (Zea mays L.) synthetic EPS12. The direct response of the EPS12 population to three cycles of selection to reduce tunnel length damage by PSB while maintaining yield was evaluated. [S.sub.0] (cycles of selection) and [S.sub.1] (selfed cycles of selection) generations and testcrosses to three testers were evaluated under artificial infestation with two corn borers, PSB and European corn borer (Ostrinia nubilalis Hubner) (ECB). Genotypes and the genotype x environment interaction were significant for tunnel length and yield. Differences among cycles of selection were significant for tunnel length, and the linear decrease for this trait (-1.80 cm [cycle.sup.1]) achieved during selection accounted for most of these differences. Yield was not significantly reduced with selection. Inbreeding for yield significantly increased due to selection. EPS12 crossed to EP42 showed a significant increase in yield with selection, while crosses to other testers showed a nonsignificant reduction in yield. Although crosses to EP42 were not significantly different for tunnel length, the high heterosis between EPS12 and EP42 and the increased yield of EPS12 x EP42 during selection suggest that inbred lines developed from advanced cycles of EPS12 could be crossed to EP42 to generate promising hybrids. In general, resistance to PSB and ECB was improved, while yield was maintained, inbreeding was increased, and yield of the cross EP42 x EPS12 was improved.