RESISTANCE IN SOME JAPONICA RICE CULTIVARS TO RICE TUNGRO SPHERICAL VIRUS

Four rice waika virus (RWV)-resistant japonica rice cultivars, Aichi A sahi, Kimmaze, Nishikaze and Saikai 139, and RWV-susceptible cultivar Reiho were tested for their resistance to rice tungro spherical virus (RTSV). Seedlings of the cultivars were artificially inoculated with R TSV plus rice tungro bacilliform virus (RTBV) by viruliferous green le afhopper, Nephotettix virescens (GLH), and virus infections were deter mined by the enzyme-linked immunosorbent assay (ELISA). Seedling infec tion with RTSV was low in the four RWV-resistant cultivars in contrast with RTSV infection in Reiho, which was as high as in susceptible che ck cultivar Taichung Native 1 (TN1). The antibiosis test showing that all the four cultivars were susceptible to the vector GLH indicates th at the low RTSV infection in the cultivars were due to their resistanc e to RTSV infection. Furthermore, the low ELISA value for RTSV of the four cultivars suggests that the cultivars were also resistant to RTSV multiplication. All these cultivars were susceptible to RTBV infectio n and its multiplication. These results support the conclusions of ear lier reports suggesting that RWV was identical with or closely related to RTSV. Among other 17 cultivars tested, those reported to be highly resistant to RWV (SHIMURA et al. 1978) were found to be resistant als o to RTSV infection. The lineage study on the four RWV-resistant culti vars showed that the RTSV resistance of these cultivars was derived fr om that of traditional Japanese cultivar Takenari. The result that RWV -resistant cultivars tested were also resistant to RTSV indicates that RWV-resistant cultivars could become outstanding new gene sources for RTSV resistance of japonica cultivars, because some of the RWV-resist ant cultivars have good agronomical traits. On the other hand, RTSV-re sistant indica cultivars, such as those bred at the International Rice Research Institute (HIBINO et al. 1988) could become new gene sources for resistance to rice waika disease.