The natural occurrence of Hibiscus chlorotic ringspot virus (Carmovirus; Tombusviridae) in aibika or bele (Abelmoschus manihot) in some South Pacific Island countries

Aibika or bele (Abelmoschus manihot), a perennial malvaceous shrub, is cultivated extensively in some Melanesian countries for its highly nutritious leaves and shoot tips. During preliminary surveys of major crop species in some South Pacific Island countries, virus-like leaf symptoms were frequently found in aibika plants grown in Fiji, Papua New Guinea, Solomon Islands and Vanuatu. A virus isolated from such plants was subsequently identified as Hibiscus chlorotic ringspot virus (HCRSV). This isolate induced symptoms in indicator plant species indistinguishable from those of HCRSV from Hibiscus rosa-sinensis; both isolates induced local lesions followed by systemic leaf chlorosis in H. cannabinus (kenaf), and local lesions only in Chenopodium quinoa, Cyamopsis tetragonoloba, Dolichus biflorus, Gossypium hirsutum and Phaseolus vulgaris. Purified preparations of the isolated virus from infected kenaf seedlings contained isometric particles c.28 nm in diameter which had properties typical of carmoviruses. An antiserum to HCRSV from H.rosa-sinensis reacted with the virus from A.manihot to its homologous titre in precipitin tube tests, ELISA and immunosorbent electron microscopy, and was subsequently used in ELISA to detect infection in aibika.

HCRSV has hitherto been reported to occur only in the ornamental shrub H.rosa-sinensis (Waterworth, 1980; Lawson, 1994; Raju, 1985); its natural occurrence in a major food crop in some South Pacific Island countries is, therefore, of particular local importance. HCRSV is undoubtedly disseminated in vegetative propagules from infected aibika and H. rosa-sinensis plants; however, it is not seed-transmitted in either of its natural hosts, and its mode of local spread is unknown. It thus remains to be determined if, like some other carmoviruses (Morris & Carrington, 1988), it is transmitted by beetles, by the soilborne fungus Olpidium bornavanus, abiotically in soil, or mechanically during cultivation and harvesting.