Properties of a tomato isolate of Pelargonium zonate spot virus

Abstract

SUMMARYA manually transmissible virus isolated from tomato plants with stunting, unfruitfulness, malformation and yellow rings and line patterns of the leaves was indistinguishable from Pelargonium zonate spot virus (PZSV) in biological, physico‐chemical and serological properties. The tomato isolate (PZSV‐T) of PZSV was seed transmitted in Nicotiana glutinosa and was detected in the pollen of this host. In sap of N. glutinosa PZSV‐T lost infectivity after diluting 10‐1 to 10‐2, heating for 10 min at 35 to 40 °C or storage at 25 °C for 7 h.Virus particles were quasi‐spherical with a diameter ranging between 25 and 35 nm with a modal value of 29 nm. Particles sedimented as three components (TV, MV and BV) with sedimentation coefficients of 80S (TV), 90S (MV) and 118S (BV); component BV is probably an aggregate of TV. Particles were unstable in CsCl and CS2SO4 but formaldehyde‐stabilised particles banded at a common density of 1–268 g/cm3 in Cs2SO4. Particles contained a single protein species with mol. wt of c. 23000 and c. 18% single stranded RNA present as two species with mol. wts of c. 1.25 × 106 (RNA‐1) and 0.95 × 106 (RNA‐2). Mixtures of RNA‐1 + RNA‐2 were infectious and this infectivity was not enhanced by the addition of coat protein. Virus particles had a Tf (mid point of extinction when heated) of 63 °C and were readily dissociated by 0.1% SDS.PZSV‐T was serologically unrelated to alfalfa mosaic and to 32 isometric viruses including five ilarviruses. Some properties of PZSV resemble those of ilarviruses but others are sufficiently different to suggest that it may not be a member of this virus group.