Considerable variation in morphology (Marukawa et al., 1975a; Morrall et al., 1972; Price and Calhoun, 1975a) and pathogenicity (Marciano et al., 1983; Morrall et al., 1972; Price and Calhoun, 1975a) has been observed among isolates of S. sclerotiorum. Variation in pathogenicity have been associated with the production of pectolytic enzymes (Hancock, 1966; Lumsden, 1976, 1979), cellulase (Lumsden, 1969), hemicellulase (Hancock, 1967), phosphatidase (Lumsden, 1970), and oxalic acid (Maxwell and Lumsden, 1970; Marciano et al., 1983; Noyes and Hancock, 1981). However, variation in these factors does not appear to be the primary determinant of pathogenicity as correlations have not always been apparent (Marciano et al., 1983; Morrall et al., 1972). In S. trifoliorum, a degenerate non-virulent isolate of the pathogen produces more protopectinase than a normal strain but only the normal isolate secretes a toxin and is considered virulent (Held, 1955). Little information is available on additional mechanisms that affect virulence among isolates of S. sclerotiorum.
KeywordsSclerotinia Sclerotiorum Vegetative Compatibility Group Agricultural Population Pathogenic Variability Typical Colony Morphology
Unable to display preview. Download preview PDF.