Tospoviruses that have single-stranded, negative sense RNA genomes are members of the Tospovirus genus, the Bunyaviridae family. Tomato spotted wilt virus is the type species of this genus. They are transmitted in a persistent manner by thrips belonging to the genera Ceratothrioides, Dictyothrips, Frankliniella, Scirtothrips, Sericothrips and Thrips and seriously damage vegetables and ornamental crops worldwide. In this report, the current state of knowledge on the biological and genetic structure, transmission mode and classification of tospoviruses are reviewed. The natural occurrence, endemicity and vector insects of tospovirus strains belonging to 29 distinct species including 8 species in Japan are described.
The incidence of apple scab, caused by V. inaequalis, has gradually decreased in recent years, while the incidence of Japanese pear scab, caused by V. nashicola, has been high. For that reason, the effects of high temperature on conidial germination and mycelial survival were investigated. Conidial germination of V. inaequalis was strongly inhibted at 35°C and 40°C as compared with that of V. nashicola. Mycelia of V. inaequalis did not survive at 40°C, but mycelia of V. nashicola did. From these results, conidial germination and mycelial survival of V. inaequalis seems to have lower tolerance than V. nashicola to high temperature. Therefore, a primary factor in the recent decrease of apple scab incidence may be due its greater sensitivity to high temperatures compared with Japanese pear scab fungus, even though the two kinds of fungi have almost the same epidemiological traits.