The effect of relative humidity and temperature on survival and growth of Botrytis cinerea and Sclerotinia sclerotiorum

Tests with mycelium and conidia of five strains of Botrytis cinerea and mycelium of three strains of Sclerotinia sclerotiorum have shown that survival and growth of these organisms depended on relative humidity, temperature, and type and strain of organism. Survival of mycelium of both organisms in the absence of nutrients, for example, varied from 12 months at 95–100% relative humidity and 0 °C to less than 1 month at below 95% relative humidity and 20 °C, depending on strain. When nutrients were present growth occurred at solution equilibrium relative humidities over 93%; at equilibrium relative humidities below 93% no growth occurred and mycelium survived only up to 1 month. Growth rates of all strains of both organisms were similar between −0.8 and 35 °C with maximum rates at about 20 °C. Results also showed that mycelium and conidia of B. cinerea survive under the conditions at which vegetables are usually stored but that mycelium of S. sclerotiorum in most instances does not.