Studies on a strain of raspberry ringspot virus occurring in England

Abstract

SUMMARYA strain of raspberry ringspot virus (RRV‐E) infecting blackberry in Essex was transmitted by inoculation of sap to twenty‐six herbaceous species, and caused symptoms in Nicandra physaloides, Datura metel and Gomphrena globosa that differentiated it from the Scottish strain of the virus (RRV‐S). In sap, with an infection end‐point of 10‐5, it was inactivated in 10 min. at 74° C, and in 5 weeks at 23° C. It was precipitated without inactivation by a 30% acetone or 30%‐saturated ammonium sulphate solution, but was inactivated when acidified to less than pH 4. Partially purified preparations of RRV‐E contained approximately equal amounts of three components with sedimentation rates of 50, 90 and 127S; electron micrographs of preparations mounted in neutral sodium phosphotungstate showed three kinds of particles with diameters about 30 mμ but with different internal structure. A preparation of RRV‐S contained a main component with a sedimentation rate of 129s, and a minor one with 50S. Petunia hybrida, cucumber and French bean seemed equally susceptible to infection with RRV‐E when grown in soil containing the nematode vector Longidorus macrosoma, but inoculation of sap infected the roots of P. hybrida much more readily than roots of the other two species. Cucumber seedlings became infected when exposed for 1 day to infective L. macrosoma, and virus‐free L. macrosoma acquired the virus from plants in 4 days. Infective L. macrosoma transmitted readily at 20° C, occasionally at 25° C, and not at 30° C; feeding seems inhibited at 30° C. RRV‐E was transmitted to seedlings grown in soil containing L. macrosoma that had been kept free from plants for 34 days. Of sixty‐eight extracts of infective L. macrosoma inoculated to Chenopodium quinoa plants, only one caused infection.