HOST ADAPTATION AND REPLICATION PROPERTIES OF 2 BIPARTITE GEMINIVIRUSES AND THEIR PSEUDORECOMBINANTS

To investigate factors involved in host adaptation and specificity of bipartite geminiviruses, the infectivity of bean dwarf mosaic (BDMV) a nd tomato mottle (ToMoV) geminiviruses and the BDMV/ToMoV pseudorecomb inants [BDMV DNA-A + ToMoV DNA-B (BA+TB) and ToMoV DNA-A + BDMV DNA-B (TA+BB)] in Phaseolus vulgaris, Lycopersicon esculentum, Nicotiana ben thamiana, and N. tabacum plants was determined. Additionally, replicat ion of these viruses was examined in protoplasts prepared from N. taba cum BY2 and Xanthi-nc cells. In adapted hosts and the permissive exper imental host, N. benthamiana, BDMV and ToMoV infected nearly 100% of i noculated plants, induced severe symptoms, and had high levels of both DNA components. In nonadapted hosts, BDMV and ToMoV infected approxim ately 40% of inoculated plants, induced no symptoms, and had reduced l evels of both DNA components. For the pseudorecombinants, symptoms wer e observed only in TA+BB-infected N. benthamiana and P. vulgaris plant s. In the other pseudorecombinant/host combinations, symptomless infec tions were detected and some plants were infected with the DNA-A compo nent only. Symptom development and/or higher infection rates for the p seudorecombinants were correlated with the host-adapted DNA-B componen t, and pseudorecombinant-infected plants had reduced levels of DNA-B. Protoplast replication assays revealed inefficient DNA-B replication f or the pseudorecombinants, and differences in viral replication proper ties in the two N. tabacum cell lines.