Growth, Sporulation, and Pathogenicity of the Raspberry Pathogen Under Different Temperature and Moisture Regimes.

Phytophthora root rot of raspberry, which is mostly caused by , is a significant issue for the Washington State red raspberry industry. Considered a cool weather pathogen, it is often assumed that it is most active and infective during the cool, wet winters of the region when soil temperatures range from 5 to 10°C; however, there are little data to support this view. More recent research has found that symptoms of root disease during late summer were strongly associated with . Therefore, experiments were conducted at four temperatures from 5 to 20°C to evaluate the effects of temperature on mycelial growth and sporulation and the effects of both temperature and soil moisture on the pathogenicity of on red raspberry. At 20°C, grew fastest and sporulated the most heavily. However, disease was most severe at both 15 and 20°C. The soil moisture parameters tested did not affect the pathogenicity results. These results show that is more likely to infect during the spring and summer months (from May through September), when soil temperatures are consistently in the range of 15 to 20°C.