Partial characterization of cucumber mosaic virus isolates from citrus and grapevine.

Three mechanically transmissible viruses recovered from grapevine (isolate YA200) and lemon (isolate L43) in Turkey and from sweet orange (isolate OR) in Italy, were identified as new strains in the subgroup IA of Cucumber mosaic virus (CMV). Particle morphology, electrophoretic pattern of viral nucleic acids, molecular hybridization with CMV-specific riboprobes, and reactions of experimental test plants, conformed to those of CMV. However, differences were observed in the cytopathology. Furthermore, unlike most CMV isolates, none of the strains under study induced the typical fern leaf symptom in tomato, and all systemically infected Chenopodium quinoa and Vigna unguiculata. In the latter, local infection by YA200 was characterized by very few necrotic lesions, whereas no local lesions were induced by L43 and OR. Partial sequencing of RNA-2 showed that amino acid changes occur in the gene coding for protein 2a of all three isolates, a condition that, as shown with other virus strains (CMV-B, CMV-L) seems to confer ability to infect V. unguiculata systemically. YA200, L43 and OR supported replication of a necrogenic satellite RNA, when added to the inoculum as a biologically active transcript. However, the expected necrotic phenotype was co-determined in ‘Rutgers’ tomato seedlings only by YA200. Unlike YA200, L43 and OR were destabilized by organic solvents used for purification and were thermosensitive, since symptom appearance in herbaceous hosts was strongly inhibited at temperatures above 25°C. CMV has already been recorded from grapevine, but citrus (sweet orange and lemon) represents an addition to the already very wide natural host range of this virus.