Effects of temperature, moisture, substrates and soil coverage on sclerotium germination and hyphal growth of Southern blight of apple in China

Southern blight, caused by Sclerotium rolfsii Sacc., is a significant disease of apple in China and many other counties. Sclerotium germination and hyphal growth are two critical processes for epidemic development. Controlled experiments were conducted to study the effects of environmental conditions on sclerotium germination and hyphal growth of the pathogen. Temperature for sclerotium germination and hyphal growth of S. rolfsii ranges from 15 to 35(o)C with the optimum at 31.5(o)C. The soil water content needs to exceed 30%, and once over this threshold, soil water content did not affect sclerotium germination and hyphal growth. The rate of sclerotium germination was high in sawdust, and hyphae grew fastest in the mixture of sawdust and soil. Sclerotium germination and hyphal growth were inhibited in nursery substrate. Hyphal growth was affected by pH but to a far lesser extent sclerotium germination. Soaking in water inhibited sclerotium germination.