EFFECT OF TEMPERATURE DURING SCLEROTIAL FORMATION, SCLEROTIAL DRYNESS, AND RELATIVE-HUMIDITY ON MYCELIOGENIC GERMINATION OF SCLEROTIA OF SCLEROTINIA-SCLEROTIORUM

A study was conducted to determine the effect of sclerotial dryness, t emperature during sclerotia formation, and relative humiditiy during i ncubation on myceliogenic germination of sclerotia of two isolates of Sclerotinia sclerotiorum (Lib.) De Bary. In the absence of exogenous n utrients, sclerotia germinated more readily at 100% RH than at 95% RH or lower. Desiccation of sclerotia is an important factor affecting my celiogenic 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 dev eloped into colonies. On the other hand, fresh, untreated sclerotia ge rminated less readily and produced Limited growth of hyphae that rarel y developed into colonies. There was generally no effect of temperatur e at which sclerotia formed on germination. The incidence of seed rot and seedling wilt of sunflower was significantly (p < 0.05) higher whe n desiccant-dried sclerotia were used as inoculum rather than fresh sc lerotia.