Growth, sporulation, and pathogenicity of the raspberry pathogen phytophthora rubi under different temperature and moisture regimes

Authors: GRAHAM, KIM - Oregon State University; Beck, Bryan; Zasada, Inga; Scagel, Carolyn; Weiland, Gerald - Jerry

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2020
Publication Date: 4/30/2021
Citation: Graham, K.A., Beck, B.R., Zasada, I.A., Scagel, C.F., Weiland, G.E. 2021. Growth, sporulation, and pathogenicity of the raspberry pathogen phytophthora rubi under different temperature and moisture regimes. Plant Disease. https://doi.org/10.1094/PDIS-09-20-1916-RE.

Interpretive Summary: Phytophthora root rot of raspberry is caused by the pathogen Phytophthora rubi. This disease causes significant losses for the red raspberry industry. The pathogen is considered to be a cool weather pathogen that infects raspberries during the cool, wet winters in the Pacific Northwest when temperatures range from 5 to 10°C. However, there is little information to confirm whether this is true or not. Experiments were conducted to evaluate how the pathogen grew, sporulated, and caused disease at four different temperatures from 5 to 20°C. The pathogen grew fastest and sporulated the most heavily at 20°C compared to the lower temperatures. However, disease was most severe at both 15 and 20°C, while being least severe at 5 and 10°C. These results are important because they show that P. rubi is more likely to infect during the spring and summer months when soil temperatures range from 15 to 20°C, and not during the winter months as previously suspected.

Technical Abstract: Phytophthora root rot of raspberry, caused mostly by Phytophthora rubi, is a significant issue for the Washington State red raspberry industry. Long considered to be a cool weather pathogen, it is often assumed that this pathogen is most active and infective during the cool, wet winters of the region when soil temperatures range from 5 to 10°C; however, there is little data to support this view. In addition, more recent research found that late summer symptoms of root disease were strongly associated with P. rubi. Experiments were therefore conducted at four temperatures from 5 to 20°C to evaluate the effect of temperature on P. rubi mycelial growth and sporulation and the effect of both temperature and moisture on the pathogenicity of P. rubi to red raspberry. Phytophthora rubi grew fastest and sporulated the most heavily at 20°C. However, disease was most severe at both 15 and 20°C. Moisture parameters tested did not affect pathogenicity results. These results show that P. rubi is more likely to infect during the spring and summer months from May through September, when soil temperatures are consistently in the 15 to 20°C range. Our results also demonstrated that sporulation starts later than, and continues for a longer period of time than is reported in the literature.