First report of Phytophthora cactorum and P. citrophthora causing root rot of Ribes lobbii (Gray) in Oregon

Authors: Weiland, Gerald - Jerry

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2014
Publication Date: 1/1/2015
Citation: Weiland, G.E. 2015. First report of Phytophthora cactorum and P. citrophthora causing root rot of Ribes lobbii (Gray) in Oregon. Plant Disease. 99(1):157.

Interpretive Summary: We examined a ornamental plant production facility in western Oregon with a number of native gummy gooseberry plants (Ribes lobbii) that were wilting and dying from an unknown disease. Further examination showed that the roots of affected plants were rotted. We isolated two pathogens from diseased plants that were identified as Phytophthora cactorum and P. citrophthora. We inoculated healthy gooseberry plants with both pathogens and were able to reproduce the original disease symptoms, confirming that P. cactorum and P. citrophthora are the causal agents. This research is important because it is the first time that these two Phytophthora species have been reported to cause disease on gummy gooseberry. This information will help ornamental plant growers become aware of significant diseases affecting gummy gooseberry and will allow researchers to develop control methods for this disease.

Technical Abstract: Ribes lobbii is an ornamental shrub native to the western United States that is grown for its pendulous red and white flowers, bristly fruit, and aromatic foliage. In 2013, we observed a number of R. lobbii plants that were wilting and chlorotic in a production facility in western Oregon. The fine roots of affected plants were rotted and larger roots exhibited numerous necrotic lesions. Two Phytophthora species were isolated from infected plants and identified as P. cactorum and P. citrophthora. A single isolate of each species was used to inoculate healthy R. lobbii plants and confirm pathogenicity. All inoculated plants died within a week after inoculation and both pathogens were successfully reisolated. Therefore, this is the first report of P. cactorum and P. citrophthora as root rot pathogens of R. lobbii.