Ecological factors have been studied to reveal the effect of the conditions of soil on the development of apothecia of Sclerotinia sclerotiorum. The different genotypes of the soils determined the sporogenesis. Most apothecia were developed on the surface of soddy alluvial and sandy soils. Strong correlations have been found between the physical, chemical and microbiologycal features of soil and the intensity ofapothecia development. The susceptibility of sunflower was studied in the field. NS-H-45, NS-11-43, S-2151 and U 55E, S-281, U 74E were tolerant to Sclerotinia sclerotiorum caused by spontaneus infection and inoculation in the field.