To prepare an field soil modeled for ecological study of Pythium spp., the field soil was heat-treated with water vapor-saturated air for eliminating native populations of Pythium spp. without disturbing physical and chemical properties of the soil. Oospores of P. spinosum or P. aphanidermatum were then introduced to the treated soil and the untreated soil to observe their germination patterns. These patterns varied with species and seasons, but there was few difference between the soils.
In the fall of 1989, a new disease was found on Sesbania, tropical leguminous manure crops, in Niigata, Japan. Dark green to grayish brown lesions appeared on the stems, petioles, leaf blades and pods of the plants. A species of Botrytis was isolated from those lesions. The fungus isolated was pathogenic to fruits of eggplant, cucumber and green pepper. Conidia were obovoid to ellipsoid, 1-celled, hyaline or pale brown. The optimum temperature for mycelial growth was 20-25°C on PSA medium. The causal agent was identified as Botrytis cinerea Persoon. “Gray mold of Sesbania” was proposed to the disease.