FURTHER STUDIES ON RASPBERRY RINGSPOT AND TOMATO BLACK RING, SOIL-BORNE VIRUSES THAT AFFECT RASPBERRY

Raspberry ringspot virus (RRSV) was found in eastern Scotland and Wiltshire infecting several varieties of raspberry, several weed species and sugar beet. Serological tests, and protection tests in Petunia hybrida, showed that isolates from different host species found at several localities in eastern Scotland were more closely related to one another than to the isolate from Wiltshire. RRSV was readily transmitted to Chenopodium amaranticolor by mechanical inoculation of sap from diseased raspberry but less readily to other species. Both the symptoms shown by C. amaranticolor, French bean, tobacco and Petunia hybrida, and its behaviour in serological and plant-protection tests, distinguished RRSV from tomato black ring, raspberry yellow dwarf, tobacco ringspot and cucumber mosaic viruses. Preparations of RRSV lost infectivity when diluted 10(-4), kept for 3 weeks at 18 degrees C., or when heated for 10 min. at 70 degrees C. but not at 66 degrees C. RRSV was precipitated without being inactivated by ammonium sulphate, ethanol or acetone. It was inactivated at pH 3. The beet ringspot strain of tomato black ring virus was isolated from the raspberry varieties Malling Seedling V and Malling Exploit by mechanical inoculation of sap to Chenopodium amaranticolor, but not from other varieties growing in virus-infested soil. RRSV and the beet ringspot strain of tomato black ring virus are soil-borne. They infected plants grown under glass in soil collected from several different fields: the incidence of infection differed in different soils, but infection by each virus was favoured by the same samples of soil. Infection with tomato black ring virus occurred equally in soil collected at different times of the year. Treatment with formaldehyde or parathion made soil non-infective. Attempts to detect virus in extracts of virus-containing soils, and to make autoclaved soils infective by watering them with virus suspensions or by growing artificially infected plants, failed, suggesting that infection depends on some factor other than free virus, possibly the presence of an organism.