Factors limiting the survival of Ascochyta spp. of peas in soil

A. pinodella and A. pinodes survived over a 12-month period in inoculated sterile soil maintained at a temperature range of −20 to 25 °C. Cultures isolated from soil from −20 °C to 15 °C were pathogenic; however, cultures isolated from soil at 5 and 10 °C were more virulent. A. pisi survived in soil at −20 and 5 °C for 12 months but only cultures isolated from −20 °C soil were pathogenic. The ability of soil cultures A. pinodella and A. pinodes to form chlamydospores is considered to a be a factor in their survival over this period of time and temperature range. No chlamydospores were formed in soil cultures of A. pisi. A. pinodella and A. pinodes were both antagonistic to A. pisi in sterile soil plates and A. pinodella was antagonistic to A. pinodes. Ascochyta spp., either A. pinodella or A. pinodes, were isolated from 18 of 46 soil samples collected from many areas in Canada. Soil cropped to corn contained fewer Ascochyta propagules than did soil cropped to beans, turnips, or peas; the latter soils contained the most propagules.