Purification and properties of cassava green mottle, a previously undescribed virus from the Solomon Islands

Abstract

SUMMARYA sap‐transmissible virus obtained from cassava with a green mottle disease occurring at Choiseul, Solomon Islands, was transmitted to 30 species in 12 plant families and was readily seed‐borne in Nicotiana clevelandii. In cassava plants infected by inoculation with sap, the first leaves to be infected systemically developed a mottle with some necrosis whereas leaves produced subsequently were symptomless but contained the virus. Most other species developed chlorotic or necrotic local lesions and systemic mottle or necrosis. This was followed, in several species, by production of small symptomless virus‐containing leaves. The virus was cultured in N. clevelandii; Chenopodium quinoa was used for local‐lesion assays. Leaf extracts from infected N. clevelandii were infective after dilution to 10–5 but usually not at 10–6, after heating for 10 min at 60°C but not at 65°C, and after storage at 20°C for at least 12 days. The virus has isometric particles of 26 nm diameter which sediment as three components, all containing a protein of mol. wt c. 53000. The two fastest sedimenting components respectively contain single‐stranded RNA of mol. wt, estimated after glyoxylation, c. 2.9 × 106 and 2.3 × 106. Both RNA species are needed for infection of plants. In tests with antiserum prepared to purified virus particles, the virus was detected in cassava and N. clevelandii by gel‐diffusion precipitin tests, by immunosorbent electron microscopy and by ELISA. Despite its similarity to nepoviruses, the virus did not react with antisera to 18 members of the group. It was named cassava green mottle virus and is considered to be a previously undescribed nepovirus.