Recurrent Selection for Resistance to European Corn Borer in a Corn Synthetic and Correlated Effects on Agronomic Traits1

Abstract

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.