Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/1998
Publication Date: N/A
Interpretive Summary: Corn with resistance to damage by fall armyworm and southwestern corn borer has been developed and released by USDA-ARS scientists at Mississippi State, MS. This corn germplasm is being used by commercial seed companies to produce hybrids with insect resistance. Determining what factors make this germplasm resistant to insect damage will make transferring this resistance into high-yielding, commercially available hybrids easier. This investigation was undertaken to determine the associations between various physical and chemical chracteristics of corn plants and resistance to fall armyworm and southwestern corn borer damage. Resistance to insect damage increased as the corn plant matured. Hemicellulose was higher in resistant plants than susceptible plants and appeared to be associated with resistance to fall armyworm damages. Relative amounts of protein, fat, lignin, and cellulose did not appear to be associated with resistance. As plants mature, leaves change from adult blue juvenile type to a brighter green adult type that results from differences in type and amount of epicuticular waxes. Resistant corn plants were found to possess 3 to 5 fewer juvenile-type leaves than susceptible plants. This trait may prove useful in identifying additional sources of resistant corn germplasm, and as a selective marker for resistance in breeding programs.
Technical Abstract: Corn, Zea mays L., germplasm with resistance to leaf feeding by southwestern corn borer, Diatraea grandiosella Dyar, and fall armyworm, Spodoptera frugiperda (J. E. Smith), has been released. Resistant genotypes sustain less damage than susceptible genotypes. Larvae that feed on plants of resistant genotypes grow more slowly than those that feed on susceptible genotypes. Both resistant and susceptible genotypes sustain less damage at plant age as infestation increases. This investigation was undertaken to determine the associations between various chemical and physical characteristics of resistant and susceptible corn hybrids and leaf-feeding damage and larval growth on hybrids infested at different vegetative stages of growth. Leaf-feeding damage was heavier on plants infested 28 to 35 d after planting than on older plants. Larvae weighed more when plants were infested between 28 and 35 d. Larvae fed on lyophilized leaf tissue in laboratory bioassays were also heaviest when whorl tissue was collected from plants 28 to 35 d after planting. Resistant hybrids completed the transition from juvenile to adult earlier than susceptible hybrids. Leaves of susceptible hybrids were less tough than leaves of the resistant hybrids, and toughness increased with plant age. Relative amounts of hemicellulose were higher in resistant genotypes and in older plants of all genotypes. Hemicellulose levels appear to be associated with fall armyworm resistance, but not southwestern corn borer.