Factors Influencing Pre‐emergence Mortality in Peas

SUMMARY Seedling emergence of 25 samples of wrinkle‐seeded peas ( Pisum sativum L.) was determined in unsterilized soil and sterilized sand at 15°C in the laboratory, and in a spring sowing in the field. Seed exudate from the seed samples was examined by steeping seed in water for 24 hours and measuring the electrical conductivity of the steep water and its soluble carbohydrate content. Significant correlations were found between the amount of exudation and the number of viable seed in the test samples (negative) and between the amount of exudation and the predisposition of the viable seed to pre‐emergence mortality (positive). Samples containing a large proportion of seed that readily exuded into steep water showed poor emergence in soil, both in the laboratory and in the field. Pythium spp. were isolated from ungerminated seeds taken from the field and laboratory soil. The role of exudates in stimulating fungal pathogens in soil is discussed as a possible explanation for the association between exudation and predisposition to pre‐emergence mortality. A routine test for indicating seed samples of potentially low field emergence is suggested.