Occurrence of botrytis leaf blight, anthracnose leaf spot, and white blister rust on Wasabia japonica in British Columbia

Abstract

Diseases of wasabi (Wasabia japonica) are the most important reason for crop failure in commercial greenhouses, and expanding disease issues highlight the importance of identifying the causal agents. Diseased wasabi leaves were collected during 2013–2015 from greenhouses in the Fraser Valley of British Columbia. Isolations from plants showing symptoms of leaf spot and blight yielded a Botrytis sp. and a Colletotrichum sp. when plated onto PDA. In addition, pustules containing sporangiospores of an Albugo sp. were observed on naturally infected leaves. Molecular identification using the ITS1–ITS4 region of rDNA revealed the pathogens isolated from wasabi leaves were B. cinerea and C. higginsianum, while the Albugo species was A. candida. The B. cinerea isolates were shown to be weakly pathogenic, infecting only succulent and senescing or wounded leaves. Inoculation studies with C. higginsianum showed that it caused lesions on Brassica juncea (mustard) leaves and on wasabi, but not on Medicago sativa (alfalfa). In culture, fastest growth occurred at 25 and 30°C, and the highest conidial production after 7 days occurred under continuous darkness. Isolates of A. candida collected from naturally infected Capsella bursa-pastoris (shepherd’s purse) plants were identical to those from wasabi plants. These previously unreported pathogens on wasabi in Canada will continue to provide challenges to commercial producers and further research into disease control methods is warranted.