First Report Of Wasabi Mottle Virus Causing Ringspot And Vein-Clearing Symptoms On Wasabi (Wasabia Japonica) In North America

Symptoms of ringspots and vein-clearing were observed on wasabi (Wasabia japonica(Miq) Matsum) plants in three greenhouses in British Columbia during 2017. Ten indicator plant species, including fourNicotianaspecies, were inoculated with sap extracts from symptomatic leaves; after 4-11 days, necrotic lesions developed on all plants. Transmission electron microscopy revealed rod-shaped virions, 250-300 nm in length, in leaves ofN. occidentalisandN. clevelandii. Total RNA from symptomatic wasabi tissues was used in RT-PCR with universal primers corresponding to five virus genera and specific primers for turnip ringspot virus and alfalfa mosaic virus. Amplicons similar to 400 bp in size were obtained with tobamovirus primer set TobN up3/TobN do4 and amplicons of similar to 300 and similar to 600 bp were obtained with ilarvirus primer set Ilar1F5/Ilar1R7. Sequencing and MegaBLAST (NCBI) query of the Ilar amplicons showed 99% identity to wasabi mottle virus (WMoV), a member of the genusTobamovirus. Next-generation Sequencing confirmed WMoV as the only virus present in diseased plants. BC isolates (GenBank accession no. MK431779) showed 99.43% sequence identity to isolate 'Alishan' (GenBank accession no. KJ207375.1) and 98.62% identity to 'Tochigi' strain (GenBank accession no. AB017504.1). Mechanical inoculation of wasabi cultivars 'Green Thumb' and 'Daruma' produced ringspots and vein-clearing symptoms after 22-23 days on the former while the latter was asymptomatic, but WMoV was detected in all plants by RT-PCR. WMoV may have been introduced into Canada on imported infected 'Green Thumb' plants and subsequently spread through commercial vegetative propagation. The effects on yield or rhizome quality are yet unknown.