Identification of Albugo candida causing white blister rust of Wasabia japonica in British Columbia

Commercial plantings of Wasabia japonica (Miq.) Matsu. are expanding in the Pacific Northwest, where it is utilized in the culinary market and in sushi restaurants. The high moisture environment required to cultivate the crop has led to an increasing incidence of disease and occurrence of a number of destructive root and foliar pathogens. In 2015, wasabi (cv. ‘Daruma’) grown in a research polyethylene house in Agassiz, BC showed symptoms of white blister rust, including severe blistering and sori development. Sporangiospores were collected from white blister leaf samples into a water suspension and were morphologically identified as either Albugo candida (Pers. Ex Lev) Kuntze or A. wasabiae Hara. Sporangiospores were collected from white rust infected Capsella bursa-pastoris (L.) Medik in close proximity to the crop, and were shown to be morphologically indistinct. Genomic DNA was extracted and PCR conducted using ITS1F-ITS4 fungal primers. Sequence comparison in GenBank showed both isolates were A. candida. Inoculations with sporangiospores collected from W. japonica could not confirm pathogenicity on either W. japonica or C. bursa-pastoris; however, inoculations on W. japonica with sporangiospores collected from C. bursa-pastoris resulted in small galls. Albugo white rust can be a major foliar disease of wasabi in parts of Asia, but fungicide applications can control it. In Canada and the U.S.A. there are no products currently registered for the control of white rust on wasabi, and the growing complex of diseases will continue to be a major obstacle for the industry.