Physiological Responses of an Insect-Resistant Soybean Line to Light and Nutrient Stress

Abstract

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 processes. The objectives of this field-cage study were to determine the effects of soil potassium levels and reduced light intensities on the insect resistance and growth characteristics of a Mexican bean beetle, Epilachna varivestis Mulsant, resistant soybean, Glycine max (L.) Merr., line and to evaluate foliar concentrations of 12 nutrients in plants growth under the imposed physiological stresses. The soybean line MBB 85-116 was grown on a Matapeake silt loam soil during 1989, 1990, and 1991. Variables were three rates of soil K and three levels of light, obtained through the use of field cages (3.66 m2) and shade cloth. Field cages were infested with Mexican bean beetle adults at a rate of 5-8 beetles per 0.3 m of row. Soil K, Mg, Ca, and pH were significantly higher at the high K rate. Potassium was the only measured foliar 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 bean beetle feeding damage resulted in significant changes in concentrations of 10 foliar nutrients. However, none of the foliar nutrients was directly associated with Mexican bean beetle resistance. A 58% reduction in light resulted in a 6.3% increase in Mexican bean beetle feeding damage. These results indicated that the factors responsible for insect resistance in MBB 85-116 are altered by light intensity.