POD ROT OF DRY PEAS DUE TO INFECTION BY ASCOSPORES OF SCLEROTINIA-SCLEROTIORUM

Dry peas (Pisum sativum) were artificially inoculated with airborne ascospores of Sclerotinia sclerotiorum over an 8-day period at the pod development stage. Pod rot lesions at the flower end of pods (basal rot) developed in 71.8% of pods. Lesion incidence at the distal end of pods (end rot) averaged 17.8%, whereas that on other parts of the pod tissues averaged 11.8%. The scanning electron microscopy studies illustrated that the high incidence of basal rot was attributable to close contact between pod tissues and the stamens, which provided substrate for germination of pathogen ascospores, subsequent ramification of mycelia, and the creation of specific infection sites for the basal rot pathogen. Mycelia on anthers and filaments spread onto the pod surface and developed infection cushions consisting of compact, dichotomously branched hyphae that initiated the penetration of pod tissues. Lesions of end rot appeared most frequently on green pod tissue at the base of the senescent style. Pollen grains often were invaded by S. sclerotiorum. The role of anthers, pollen grains, filaments, and styles in the development of Sclerotinia pod rot in dry peas is discussed.