USDA-ARS Crop Improvement and Protection Research Unit, 1636 E. Alisal Street, Salinas, CA 93905
Tomato chlorosis virus (ToCV) is the second whitefly-transmitted, phloem-limited, bipartite closterovirus described infecting tomato. ToCV is distinct from tomato infectious chlorosis virus (TICV), based on lack of serological and nucleic acid cross-reactions and differences in vector specificity. TICV is transmitted only by the greenhouse whitefly (Trialeurodes vaporariorum), whereas ToCV is transmitted by the greenhouse whitefly, the banded-wing whitefly (T. abutilonea), and Bemisia tabaci biotypes A and B (B. argentifolii). Double-stranded (ds) RNA analyses of ToCV show two prominent dsRNAs of approximately 7,800 and 8,200 bp, with several small dsRNAs. Digoxigenin-11-UTP-labeled riboprobes derived from cDNA clones representing portions of RNAs 1 and 2 were used in Northern blot hybridizations to detect two large nonhomologous dsRNAs and a subset of smaller dsRNAs. These probes were used in dot blot hybridizations to detect ToCV in infected tomato. Inclusion bodies and cytoplasmic vesicles were consistently observed in phloem tissues of ToCV-infected Nicotiana clevelandii. Computer-assisted sequence analysis showed significant homology between ToCV clones that hybridize specifically with RNAs 1 and 2 and the lettuce infectious yellows virus methyltransferase of RNA 1 and the HSP70 heat shock protein homolog of RNA 2, respectively. Thus, ToCV is another member of the growing subgroup of bipartite closteroviruses transmitted by whiteflies.