Attenuated isolates of cucumber mosaic virus produced by satellite RNA and cross protection between attenuated isolates and virulent ones.

Abstract

Cucumber mosaic virus (CMV) has four major RNA segments, which are named RNA 1, 2, 3 and 4 in order of decreasing molecular weight. The largest three RNAs are essential for the manifestation of the infectivity of the virus, and RNA 4 is a subgeno-mic fragment of RNA 3. Recently, the existence of another low molecular weight satel-lite RNA, i.e. the fifth RNA, associated with the replication of CMV has been re-ported1-8). Kaper and Waterworth4) showed that CMV-S containing the satellite RNA (CARNA 5) induced lethal necrotic symptoms on tomato, and Takanami7) also reported striking changes in the symptoms on CMV-infected plants by the addition of the satel-lite RNA. Mossop and Francki6) showed that Sat-RNA attenuated symptoms of CMV on Rutgers tomato plants. In 1982, necrotic disease of tomato plants (Fig. 1) was observed in Ohno and Nanae, southern Hokkaido, and an isolate of CMV, designated as CMV-P(n), was found to be the causal agent of the disease9). A small RNA was detected among the RNAs of CMV-P(n)10), and it had a satellite nature similar to that of CARNA 54) or satellite RNA7) previously reported. This satellite RNA which was isolated from CMV-P(n), and des-ignated as (n)RNA 5, caused necrosis on tomato plants only when it was simultaneouly inoculated with satellite-free CMV.