Four Botrytis species of B. allii, B. cinerea. B. squamosa and B. fabae were examined for their responses of conidium and sclerotium formation to continuous irradiation with near ultraviolet radiation (NUV) and continuous darkness at temperatures between 5 and 30℃ on the V-8 vegetable juice agar plates and on the host tissues. The number of conidia formed under darkness relative to that under NUV was greatest in B. allii, followed by B. cinerea and B. squamosa. Botrytis fabae did not form conidia under darkness. Dependency on the NUV for conidium formation was greater on the VJA plates than on the respective host tissues. Conidium formation of B. fabae was completely dependent on the NUV, even on its own host tissues. Favorable conditions of light and temperature for conidium formation and those for sclerotium formation were different. There was an antagonistic relationship between conidium formation and sclerotium formation. Sclerotia formed under conditions that were unfavorable for conidium formation of Botrytis species and for epidemic of the disease caused by the fungi. These results support the ecological role of sclerotia that are formed as a resting structure and serve as an organ for survival of the fungus under adverse conditions, while conidia are formed as dispersal propagules.