Leaf Feeding Resistance to Multiple Insect Species in a Maize Diallel

The southwestern corn borer (SWCB), Diatraea grandiosella Dyar, and the sugarcane borer (SCB), D. saccharalis F., are important pests of maize, Zea mays L., in some regions of the Americas. The European corn borer (ECB), Ostrinia nubilalis Hübner, is a major maize pest in temperate North America and Europe. Germplasm with resistance to leaf feeding by these insect species was developed at the International Maize and Wheat Improvement Center (CIMMYT) in Mexico, but little was known about the inheritance of resistance in this germplasm. A 10-parent diailel cross of eight CIMMYT inbreds and two susceptible public inbreds was evaluated for leaf feeding by SWCB, SCB, and ECB in separate trials. General combining ability (GCA) for leaf feeding rating was a significant source of variation among F₁'s under artificial infestation with each of the three insect species. Variation due to specific combining ability (SCA) was not significant. Both leaf feeding ratings for F₁'s and estimated GCA effects were highly correlated between SWCB and SCB infested trials, indicating that selection for resistance to one species probably confers resistance to the other in the materials in the study. ECB leaf feeding ratings of the F₁'s and GCA effects were also highly significantly correlated with those of the other two species, but correlation coefficients were slightly lower than those between SWCB and SCB. ECB is the least aggressive leaf feeder in this study, hence selection for resistance to ECB may not confer resistance to SWCB or SCB, but selection for resistance to SWCB or SCB appears to confer ECB leaf feeding resistance. Some inbreds developed from CIMMYT's multiple borer resistant (MBR) population showed good leaf feeding resistance to all three insect species. Breeding methods that take advantage of additive genetic variance should be effective in utilizing this resistance. Part of dissertation for senior author's Ph.D. degree. Joint contribution of Cornell University and CIMMYT. Cornell Paper no. 803. Research supported in part by funds from USAID Grant no. DAN-1406-G-SS-7087-00 and Hatch Project no. NY (C) 149412.