Properties of spinach yellow mottle, a distinctive strain of tobacco rattle virus

A virus (isolate SYM) obtained from spinach plants in England with a severe yellow mottle disease induced symptoms resembling those of tobacco rattle virus (TRV) in several indicator species but caused systemic necrosis in Chenopodium amaranticolor and C. quinoa. It was transmitted to bait plants grown in soil containing the nematode Trichodorus primitivus. Purified virus preparations contained rod-shaped particles that were predominantly of four modal lengths: 188 nm (L particles), 101 nm (S particles), 57 nm and 48 nm (together called VS particles), containing RNA with mol. wts of 2.4, 1.5, 0.7 and 0.6 million, respectively. L particles (s°₂₀= 300 S) and S particles (230 S) greatly outnumbered VS particles (c. 150 S). All particles contained a single polypeptide species with estimated mol wt of 24 700, slightly larger than those previously reported for tobraviruses. Purified L particles were infective but both L and S particles were needed to induce the production of virus nucleoprotein particles. VS particles were not infective and apparently had no qualitative or quantitative effect on infection by L or by L plus S particles. S particles carried determinants for serological specificity and ability to invade C. amaranticolor systemically. Isolate SYM produced pseudo-recombinants with isolate PRN of TRV. Also, isolates CAM, OR and PRN of TRV, and isolate SYM, were found to be distantly related by three kinds of serological test. No relationship was detected between these isolates and pea early-browning virus in gel-diffusion precipitin tests or electron microscope serological tests, but a distant relationship between isolate SYM and pea early-browning virus was found by micro-precipitin tests. Isolate SYM therefore has closer affinities with TRV than with pea early-browning virus and is considered to be a distinctive strain of TRV.