BIOLOGY OF Alternaria alternata, THE CAUSAL AGENT OF BLACK POD DISEASE OF WHITE BEAN IN SOUTHWESTERN ONTARIO

Abstract

During the growing season Alternaria alternata was isolated from leaves of many weed species commonly found in or around a bean (Phaseolus vulgaris L.) field. The fungus was also found on bean plants at all stages of growth. Population densities of A. alternata on the leaves of bean plants grown from surface-sterilized and non-sterilized seeds were similar. Population densities of A. alternata on the leaves of weeds and beans increaased as the growing season advanced. The increase in the population of A. alternata was correlated with natural senescence of leaf tissues. Sugars and ninhydrin positive substances (NPS) in the leaf wash increased with plant age. At a given growth stage, the concentration of sugars and NPS found in leaf washes of cultivars susceptible to A. alternata were higher than those tolerant to it.Key words: Bean (field), Alternaria alternata