VARIATION IN CULTURAL MORPHOLOGY AND VIRULENCE AMONG PROTOPLAST-REGENERATED ISOLATES OF SCLEROTINIA-SCLEROTIORUM

The influences of source isolates and exposure to polyethylene glycol (PEG) on variations in cultural morphology and virulence among protoplast-regenerated isolates of Sclerotinia sclerotiorum were determined. More than 50 germinated protoplasts were isolated from each of three source isolates. One-half of the regenerants were exposed to a PEG treatment, and one-half were unexposed. Source and regenerate isolates were compared for variations in cultural morphology on potato-dextrose agar and in lesion diameters produced on celery petioles. Qualitative variations in cultural morphology, color, and sclerotial production occurred in most treatments. Quantitative variations in lesion diameters also occurred in most treatments, but interactions among isolates and PEG treatments were not significant. The stability of variation in selected regenerants was evaluated by serial transfer and evaluation of colony morphology and virulence for five subcultures after regeneration. Depending on the source isolate used, variation in regenerants tended to be unstable and to revert back to the characteristics of the source isolate. However, several virulent regenerants that did not produce sclerotia in culture were obtained. The results indicate that protoplast methods can be used for the production and isolation of isolates with unique characteristics.