Effect of temperature during sclerotial formation, sclerotial dryness, and relative humidity on myceliogenic germination of sclerotia of Sclerotinia sclerotiorum

Abstract

A study was conducted to determine the effect of sclerotial dryness, temperature during sclerotia formation, and relative humiditiy during incubation on myceliogenic germination of sclerotia of two isolates of Sclerotinia sclerotiorum (Lib.) De Bary. In the absence of exogenous nutrients, sclerotia germinated more readily at 100% RH than at 95% RH or lower. Desiccation of sclerotia is an important factor affecting myceliogenic germination and hyphal growth. At high humidity, either in an atmosphere with 100% RH or on moist sand, desiccant-dried sclerotia germinated readily and produced vigorous hyphal growth that often developed into colonies. On the other hand, fresh, untreated sclerotia germinated less readily and produced limited growth of hyphae that rarely developed into colonies. There was generally no effect of temperature at which sclerotia formed on germination. The incidence of seed rot and seedling wilt of sunflower was significantly (p < 0.05) higher when desiccant-dried sclerotia were used as inoculum rather than fresh sclerotia.Key words: Sclerotinia sclerotionum, sclerotia, myceliogenic germination, sclerotinia wilt of sunflower, relative humidity.