Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 13, 1998
Publication Date: N/A
Interpretive Summary: The southwestern corn borer is a serious pest of corn in the U.S. and Mexico. When corn is attacked while in the vegetative stages, before silks and tassels emerge, larvae feed on the leaves and then tunnel into the stalk. Corn with resistance to this type of damage has been identified. When corn is attacked after silks emerge, the southwestern corn borer larvae feed on the developing ears and then tunnel into the stalk. Lodging of the stalks is common. Corn with resistance to this type of damage has not been identified. The lack of a reliable method of evaluating corn for resistance to such damage has been a major hindrance. In this investigation a group of experimental corn hybrids including some that could be potentially useful as sources of resistance were infested with larvae. Damage to leaf sheaths and husks was visually rated, and larvae were recovered and counted and weighed after 14 days. Unfortunately, the visual ratings were not useful in determining which hybrids were resistant. Differences in the numbers and weights of larvae, however, indicated that some of these hybrids possess resistance to southwestern corn borer when plants are infested after anthesis. These experimental hybrids will be useful as sources of resistance in developing commercially available corn hybrids for farmers. This will reduce yield losses.
Technical Abstract: Southwestern corn borer, Diatraea grandiosella Dyer, is an important pest of corn, Zea mays L., in the southern U.S. and Mexico. Germplasm with resistance to attack by southwestern corn borer in the vegetative stages has been released; however, resistance to attack after anthesis has not yet been identified. The objectives of this investigation were to evaluate a diallel cross among a group of inbred lines, some of which appeared to exhibit resistance in laboratory and preliminary field tests, and to evaluate the effectiveness of visual ratings of leaf sheath and husk damage in identifying resistant hybrids. The nine-parent diallel cross was grown for two years and plants were infested with southwestern corn borer larvae 7 d after anthesis. Leaf sheaths and husks were visually rated and larvae recovered, counted, and weighed 14 d after infestation. Husks were also collected from an additional planting of the diallel cross within 3 d after silk emergence, lyophilized, and used in preparation of laboratory diets. Larvae were fed on the diets for 21 d and then weighed. Leaf sheath and husk rating were not significant among hybrids; however, differences in number of larvae, mean larval weight, and total weight of larvae on a plant in the field test and mean larval weight in the laboratory among hybrids were significant. General combining ability effects indicated that the parental inbreds, Mp305 and SC213, contributed to resistance of their hybrids. Visual ratings of leaf sheath and husk damage do not appear to be sufficiently sensitive to detect relatively small differences in resistance among hybrids, but traits associated with larval survival and growth in both field and laboratory evaluations indicated resistance in some hybrids.