Ergosterol and Substitutes for the Ultraviolet Radiation Requirement for Conidia Formation In Stemphylium Solani

SUMMARY

Stemphylium solani preconidiophores respond by subsequent pigmentation and conidia production to treatment with certain solvents and carriers alone or with added ergosterol. Treatment consisted of flooding 7-day-old cultures grown in the dark at 21 C on V-8 juice 1.5% agar with 4 ml of solution so that preconidiophores are wetted or soaked for 24 hr prior to deflooding and dark incubation for another 24 hr. Conidia were induced to form by 1–10% DMSO in 0.1 M KH₂PO₄ and by 2% ethanol. Ergosterol added to carriers or solvents increased conidial formation 2- to 5-fold over that in controls. The morphology and pigmentation of conidiophores and conidia were similar to those produced by ultraviolet radiation at appropriate doses. A possible explanation is that free ergosterol is involved in the conidial formation in S. solani.