Effect of temperature on survival of Phytophthora kernoviae oospores, sporangia, and mycelium †

Phytophthora kernoviae Brasier, Beales & Kirk, recently found in the UK and New Zealand, is a pathogen of more than 30 host species. It is not known to produce chlamydospores, but is homothallic and produces abundant oospores and sporangia. This study was conducted to examine long-term survival of oospores, sporangia, and mycelium buried in sand at different temperatures. Viability of oospores buried in sand kept at 4, 10, 20 or 30 oC was assessed by staining with tetrazolium bromide solution. After 1 year at these temperatures, 82, 81, 79, and 58 % of oospores of a New Zealand isolate respectively had survived. Corresponding values for an English isolate were 86, 75, 82, and 78%. Necrosis was observed on Rhododendron L. leaf discs exposed to oospores that had been buried for 1 year at temperatures below 30 oC. Oospores exposed for 1