PHYSIOLOGICAL-RESPONSES OF AN INSECT-RESISTANT SOYBEAN LINE TO LIGHT AND NUTRIENT STRESS

Optimum or higher levels of soil potassium have been implicated with a decline in the incidence of disease and insect pests in several plant species. Light intensity is recognized as an important environmental factor that influences plant morphological and physiological logical p rocesses. The objectives of this field-cage study were to determine th e effects of soil potassium levels and reduced light intensities on th e insect resistance and growth characteristics of a Mexican bean beetl e, Epilachna varivestis Mulsant, resistant soybean, Glycine max (L.) M err., line and to evaluate foliar concentrations of 12 nutrients in pl ants grown under the imposed physiological stresses. The soybean line MBB 85-116 was grown on a Matapeake silt loam soil during 1989, 1900, and 1991. Variables were three rates of soil K and three levels of lig ht, obtained through the use of field cages (3.66 m(2)) and shade clot h. Field cages were infested with Mexican bean beetle adults at a rate of 5-8 beetles per 0.3 m of row. Soil ii, Mg, Ca, and pH were signifi cantly higher at the high K rate. Potassium was the only measured foli ar nutrient significantly greater at the high K rate. Elevated levels of soil potassium had no effect on Mexican bean beetle feeding damage and little effect on seed yield. Reduced light and increased Mexican b ean beetle feeding damage resulted in significant changes in concentra tions of 10 foliar nutrients. However, none of the foliar nutrients wa s directly associated with Mexican bean beetle resistance. A 58% reduc tion in light resulted in a 63% increase in Mexican bean beetle feedin g damage. These results indicated that the factors responsible for ins ect resistance in MBB 85-116 are altered by light intensity.