INVITRO INITIATION OF SCLEROTIA OF SCLEROTIUM-CEPIVORUM

Sclerotium cepivorum, the causal agent of white rot of Allium species, survives in soil by means of small, black, spherical sclerotia formed on the roots and bulbs of infected host plants. Factors responsible for the initiation of sclerotium formation in nature are unknown. When grown in culture on potato dextrose agar at 17 +/- 1-degrees-C, S. cepivorum forms sclerotia about 4 days after full colonization of the surface of the medium, regardless of the elapsed time from inoculation. Restriction of mycelial growth in S. cepivorum after a period of rapid growth and expansion initiates sclerotium formation. Growth may be restricted by physical, nutritional, competitive, or antagonistic factors. Physical injury to the mycelium and staling products do not induce sclerotium formation in S. cepivorum.