Response of Two Maize Synthetics to Recurrent Selection for Resistance to First-Generation European Corn Borer (Lepidoptera: Pyralidae) and Diplodia Stalk Rot

Abstract

Four cycles of recurrent selection in two maize, Zea mays L., synthetics, BSAA and BSBB, were done to select for resistance to first-generation European corn borer (ECB), Ostrinia nubilalis Hubner, and Diplodia ( Diplodia maydis [Berkeley] Saccardo) stalk rot (DSR). Recurrent selection was based on the evaluation of SI lines. The original synthetics and four improved cycle populations of BSAA and BSBB were evaluated in multiple environments as populations per se, crosses between synthetics, and test crosses to a susceptible tester. Two cycles of recurrent selection in BSAA and three cycles in BSBB produced populations that were as resistant to leaf feeding by the ECB as the highly resistant single-cross check, B75 x CI31A, after which no further progress was made. The realized gain per cycle of selection for BSBB (be = -0.63 units on a 1-9 scale) was highly significant and of greater magnitude than for BSAA (be = -0.10 units, nonsignificant). In contrast, highly significant linear progress for DSR resistance was made through all four cycles of selection in both synthetics (be = -0.38 and -0.36 units for BSAA and BSBB, respectively, on a 1-6 scale). The level of resistance to ECB and DSR in the population crosses and test crosses suggests that the genes governing resistance to these two traits are acting in an additive manner. Selection for resistance to DSR and ECB was associated with improvement in stalk rind strength and decreases in the incidence of stalk lodging and natural stalk rot development. The results indicate that improved stand ability in environments conducive to stalk rot development may require selection for physical stalk strength as well as for resistance to stalk-rotting organisms.