Factors Affecting Sclerotial Germination of Sclerotium cepivorum, Secondary Sclerotia Formation, and Germination Stimulants to Reduce Inoculum Density. Prudence A. Somerville, Former Graduate Research Assistant, Department of Plant Pathology, University of California, Davis 95616. Dennis H. Hall, Extension Plant Pathologist (deceased), Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 71:229-233. Accepted for publication 18 September 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0229.

Eruptive germination of sclerotia was stimulated by allyl sulfide (AS) and Allium extracts. Exposure to 2.5–5% AS (v/v) for 7 days was near optimal for stimulation of eruptive germination, whereas exposure to higher concentrations was somewhat inhibitory to total (hyphal + eruptive) germination. Incubation of sclerotia on substrates containing available nutrients also inhibited eruptive germination. Exposures to AS for 15 min were sufficient to stimulate eruptive germination, but the highest level of eruptive germination was attained after exposures of 24 hr or longer. A 6-hr exposure was required for subsequent secondary sclerotia formation. A maximum mean of three secondary sclerotia was produced per eruptively germinated primary sclerotium when sclerotia were incubated on purified agar and exposed to 2% AS for 1 wk. Applications of Allium extracts to fallow field soil induced germination of up to 60% of recovered sclerotia. Under conditions not conducive for secondary sclerotia formation and of low initial inoculum density, such reductions could reduce white rot incidence in the next crop.