Changes in Agronomic Traits Associated with Recurrent Selection in Two Maize Synthetics
The agronomic performance of two maize (Zea mays L.) synthetics, BSAA and BSBB, was investigated following four cycles of S1 recurrent selection for resistance to first-generation European corn borer (Ostrinia nubilalis Hübner) (ECB) and Diplodia (Diplodia maydis (Berk.) Sacc.) stalk rot (DSR). The original and four improved cycle populations (CO–C4), their crosses to a single-cross tester, crosses between synthetics, and three single-cross checks were evaluated in five Iowa environments. Artificial infestations of ECB and inoculations of D. maydis were used to assess the ability of genetic resistance to reduce yield losses. Highly significant grain yield reductions were observed in both synthetics per se and averaged 20% from the C0 to the C4 in the absence of disease or insect pressure. Ear length was the main component contributing to grain yield reductions. Changes toward earlier pollen date were closely associated with reductions in plant height observed in both synthetics. The level of resistance achieved in the improved populations of BSBB was sufficient to prevent grain yield losses caused by ECB infestations and D. maydis inoculations relative to a control treatment. Additional genetic studies suggested that the response of most of the agronomic traits evaluated was associated with allelic frequency changes resulting from selection. Inbreeding depression caused by random genetic drift played a small role in most traits, with the exception of grain yield in BSBB.
Copyright © 1989.