Studies on weather damage in mungbean. III. Development of a system for measuring genotypic variation in resistance to weathering

Abstract

Mungbeans are susceptible, following rainfall, to weather damage which reduces their value for food uses. Cultivars differ in their resistance to weathering, but selection for resistance based on field response has been unsuccessful. Three controlled experimental systems (immersion in water, exposure to simulated rainfall, and exposure to cyclic wetting and drying in a mist chamber) were evaluated for their ability to reproduce the symptoms of weather damage and to differentiate among the responses of cultivars known from field experience to differ in resistance. When seeds were immersed, the susceptible green gram cv. Berken absorbed water faster and had less impermeable seed than the resistant black gram cv. Regur. The green gram cv. Celera showed an intermediate response consistent with its intermediate resistance to weathering. The rainfall simulator produced more realistic conditions for weathering than seed immersion, and symptoms typical of weather damage were produced. However, the responses of cultivars were relatively poorly differentiated and the method showed poor repeatability. The exposure of podded racemes to wetting and drying cycles under controlled conditions of temperature and humidity in a mist chamber provided the most reliable method for simulating weather damage. The degree of damage increased with duration of exposure and the relative resistance of cultivars was consistent with field observation. The extent of weather damage was best measured as reduction in seed viability and as change in the appearance and permeability of the testae of seeds following exposure. The combined use of the mist chamber and these measurement criteria constitute a successful system for the selection and breeding of mungbeans for resistance to pre-harvest weathering.