STUDIES ON WATER DAMAGE IN MUNGBEAN .1. EFFECT OF WEATHERING ON SEED QUALITY AND VIABILITY

The expansion of mungbean production in Australia is severely limited by the susceptibility of current cultivars to weather damage in the fi eld. The aim of this research was to describe the causes, process, and effects of weathering in mungbean as the first step toward the breedi ng of resistant cultivars. Symptoms of weather damage were produced by exposing plants to simulated rainfall/high humidity and by subjecting seeds to cycles of wetting and drying. In both cases, symptoms progre ssed from discolouration, wrinkling, and cracking of the testa, to ger mination of the seed. Symptoms produced in controlled experiments were the same as those observed in the field. Only seeds that imbibed duri ng the wetting phase developed symptoms of weather damage on drying. E xposure to one cycle of weathering also advanced the timing and degree of damage to seeds during subsequent cycles. This was associated with an increased rate of water absorption in weathered seeds. The lowerin g of apparent resistance to weather damage with prior exposure to rain fall suggested that only protected material be screened for weathering resistance. The death of seeds remained the ultimate expression of th e changes induced by weathering.