Enhanced Recovery of Phytophthora ramorum from Soil Following 30 Days of Storage at 4°C

Chlamydospores of Phytophthora ramorum were used to infest field soil at densities ranging from 0.2 to 42 chlamydospores/cm(3) soil. Recovery was determined by baiting with rhododendron leaf discs and dilution plating at time 0 and after 30 days of storage at 4 degrees C, as recommended by USDA-APHIS. Baiting was slightly more sensitive than dilution plating in recovering P. ramorum immediately following infestation of soil and allowed detection from samples infested with as little as 0.2 chlamydospores/cm(3) compared with 1 chlamydospore/cm(3) for dilution plating. After 30 days of infested soil storage at 4 degrees C, P. ramorum was detected at significantly (P = 0.05) higher levels than at time 0 with both recovery methods. The results indicate that storage of P. ramorum-infested soil at 4 degrees C may allow for pathogen activity, such as sporangia production, which may enhance recovery from soil.