Factors Affecting Myceliogenic Germination of Sclerotia ofSclerotinia sclerotiorum

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Abstract
Sclerotia of S. sclerotiorum collected from different fields varied in ability to undergo myceliogenic germination without addition of exogenous nutrients. Of 3 samples tested from sunflower, mungbean and safflower, the frequency of germinated sclerotia was 8, 79 and 98%, respectively. These differences were not due to the existence of distinct strains because germination of daughter sclerotia produced on potato-dextrose agar was similar. Light-colored sclerotia, resulting from incomplete melanization of the rind, were found in 14 of the 15 samples collected from 5 hosts in western Canada and comprised from 0.5-85% of the sclerotia in each sample. Germination occurred readily in intact light-colored sclerotia incubated on autoclaved moist sand, but it occurred in black sclerotia only when the rind was injured. The incompletely melanized, light-colored sclerotia were more frequently contaminated with microorganisms than were the completely blackened ones. Myceliogenic germination of sclerotia is affected by the extent of melanization of the rind and that the black, melanized rind prevents germination in the absence of exogenous nutrients, and also protects sclerotia from invasion by microorganisms.