Detection of rice grassy stunt virus in planthopper vectors and rice plants by ELISA.

Abstract

Filamentous particles associated with rice grassy stunt were purified from the infected rice plants. The filamentous particles were 6-12nm in width. An antiserum to the filamentous particles specifically reacted to extracts of grassy stunt-infected leaves and -viruliferous planthoppers, Nilaparvata lugens by agar gel double diffusion test. The antibody neutralized the infectivity in extracts of grassy stunt-infected rice leaves. In enzyme-linked immunosorbent assay (ELISA), the filaments were detected in extracts of grassy stunt-exposed planthopper population up to a dilution of one planthopper/8ml and also from extracts of the infected leaves at 1/100, 000 dilution. Extracts of virus-free insects and healthy rice leaves did not give a positive reaction in ELISA. The purified filamentous nucleoprotein reacted positively even when diluted to A260=1.0×10-5. The infective planthoppers stored at 25C for 1 month and the infected rice leaves stored at room temperature for 4 months gave positve reactions, but the intensity of the reactions was lower than that in fresh or frozen materials. In the exposed planthopper populations, 40% of the insects transmitted the causal agent and gave a positive reaction in ELISA, 41% failed to transmit the agent but gave a positive reaction, while both tests were negative in the remainder. The brown planthoppers that migrated across the South China Sea were collected and tested for the presence of the filaments in ELISA in 1982. About 0.1% of the total 1, 126 individuals tested gave positive reaction.