Nonpathogenic Nilaparvata lugens reovirus is transmitted to the brown planthopper through rice plant

Nilaparvata lugens reovirus (NLRV) was found in a colony of the brown planthopper, N. lugens, an important plant virus vector. Unlike with usual phytopathogenic reoviruses, there are no visible symptoms on a rice plant which has been attacked by NLRV-infected planthoppers. Manner of transmission, host range, and multiplication of NLRV in rice plant were studied by enzyme-linked immunosorbent assay or polymerase chain reaction using reverse transcriptase. NLRV was transovumly transmitted to about 15% of nymphs. NLRV could further spread to planthoppers via rice plants through sucking by viruliferous insects. This horizontal transmission was apparently of primary importance for continuous NLRV infection to a colony of N. lugens. By corearing with viruliferous N. lugens on rice seedlings, Laodelphax striatellus acquired NLRV but Sogatella furcifera, Nephotettix cincticeps, and N. malayanus did not during the period studied. NLRV inoculated onto rice plant by viruliferous N. lugens failed to multiply, which accounts for the lack of symptoms on the plant even after an attack by viruliferous planthoppers. These biological properties and our previous data, which revealed a molecular similarity between NLRV and fijiviruses, suggest that NLRV is an ancestral virus of fijiviruses.