Abstract
Strawberry root rot was first recorded in a small area in the suburbs of Shizuoka city in 1949, where strawberries are usually grown on paddy fields after rice plants have been harvested and the flooding water has been drained off. Since then this disease has spread in the strawberry growing areas in Shizuoka Prefecture. The symptoms were always accompanied by red stele which is characteristic to the Phytophthora infection. When the roots showing the red stele symptom were immersed in water, the pear-shaped sporangia characteristic to Phytophthora appeared abundantly on the root surface. The root rot disease of strawberry occurring in Osaka and Hyogo Prefectures was also accompanied by the red stele symptom. Abundant sporangia of Phytophthora were always detected from these diseased roots. The results indicate that the root rot disease is identical with that occurring in Shizuoka Prefecture. Phytophthora sp., Fusarium oxysporum, Pythium spp., Rhizoctonia sp., and other unidentified fungi were isolated from the diseased roots. Inoculation experiments showed that only Phytophthora sp. was responsible for the unique red stele symptom. The Phytophthora sp. was identified as Phytophthora fragariae Hickman from the physiological and morphological characteristics.
