Occurrence and characterization of tomato spotted wilt orthotospovirus isolated from cucumber

Diseases associated with tomato spotted wilt orthotospovirus (TSWV) are a serious threat to vegetable production worldwide. In 2019, leaf necrosis disease was observed on cucumber plants in Fukushima Prefecture, Japan. TSWV infection was identified in the diseased plants by immunostripe tests and RT-PCR analysis. Sequencing of the complete genome of this TSWV strain showed the highest identity with previously characterized TSWV isolates, and we therefore designated the cucumber-infecting variant as TSWV-Fukushima:cucumber 2019 (TS-FC19). Phylogenetic analyses based on the intergenic regions revealed that TS-FC19 and other TSWV isolates collected from the same area clustered in a distinct clade. Cucumber plants inoculated with TS-FC19 produced leaf necrosis symptoms, whereas other TSWV strains did not induce severe symptoms in this host. Together, our findings indicate that the cucumber leaf necrosis disease in Fukushima Prefecture is caused by a new strain of TSWV that appears to have evolved locally. This is the first detailed report on the biological characteristics of a cucumber-infecting TSWV.