Tamusred mosaic virus, a potexvirus from black bryony (Tamus communis)

A virus was isolated in Italy from Tamus communis in which it caused symptoms of red mosaic and leaf distortion. The virus, for which the name tamus red mosaic virus (TRMV) is suggested, was differentiated from other potexviruses or possible potexviruses on the basis of host range, particle properties and serology. In crude preparations, TRMV had elongated particles of modal length 550–560 nm and diameter of 13 nm. TRMV was easily purified from Chenopodium quinoa and had a buoyant density of 1·34 g/cm3 in CsCl and 1·27 g/cm‐3 in Cs2SO4. An antiserum to TRMV was obtained with a titre of 1/1024 in slide precipitin tests. TRMV was related to, but distinct from, tamus latent virus, a potexvirus isolated from Tamus communis in the UK, and more distantly related to potato virus X, cactus virus X and commelina virus X. Polyacrylamide gel electrophoresis (PAGE) indicated that the virus particles contained a single protein species of estimated molecular weight 25·2 kDa. Enzymatic digestions, agarose gel electrophoresis and infectivity of the isolated nucleic acid indicated that the virus has a single major molecule of single‐stranded positive‐sense RNA of estimated molecular weight 2120 kDa (ca. 6·4 kb).