Rice Grassy Stunt Virus: A Planthopper-Borne Circular Filament

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Abstract
Two viruslike particles, threadlike filaments 6-8 nm in diameter and small isometric particles 18-20 nm in diameter, were observed in extracts of rice plants affected by rice grassy stunt disease. The filaments were abundant and the isometric particles were scarce. The filaments were purified and antiserum to the filaments was obtained. The antiserum specifically reacted with extracts of infected plants and the vector Nilaparvata lugens that had fed on rice grassy stunt-affected plants. The purified filaments were often circular and the circular filaments were 950-1350 nm in length. The filament was nucleoprotein containing RNA and a single protein species with a MW of 31,000 daltons. Purified filaments were not infective. Serologically, the filament was distantly related to rice stripe virus but not to maize stripe and rice hoja blanca viruses. Purified rice stripe virus has a circular filament 11-13 nm in diameter, with a helical configuration and with varied length. The loosened helix appeared to be constructed of a filament 6-8 nm in diameter. The serological relationship and morphological similarity between the filaments and rice stripe virus indicate that the filament is the causal virus of grassy stunt. The name rice grassy stunt virus (RGSV) is proposed for the filament.