To investigate factors involved in host adaptation and specificity of bipartite geminiviruses, the infectivity of bean dwarf mosaic (BDMV) and tomato mottle (ToMoV) geminiviruses and the BDMV/ToMoV pseudorecombinants [BDMV DNA-A + ToMoV DNA-B (BA+TB) and ToMoV DNA-A + BDMV DNA-B (TA+BB)] in Phaseolus vulgaris, Lycopersicon esculentum, Nicotiana benthamiana, and N. tabacum plants was determined. Additionally, replication of these viruses was examined in protoplasts prepared from N. tabacum BY2 and Xanthi-nc cells. In adapted hosts and the permissive experimental host, N. benthamiana, BDMV and ToMoV infected nearly 100% of inoculated plants, induced severe symptoms, and had high levels of both DNA components. In nonadapted hosts, BDMV and ToMoV infected approximately 40% of inoculated plants, induced no symptoms, and had reduced levels of both DNA components. For the pseudorecombinants, symptoms were observed only in TA+BB-infected N. benthamiana and P. vulgaris plants. In the other pseudorecombinant/host combinations, symptomless infections were detected and some plants were infected with the DNA-A component only. Symptom development and/or higher infection rates for the pseudorecombinants were correlated with the host-adapted DNA-B component, and pseudorecombinant-infected plants had reduced levels of DNA-B. Protoplast replication assays revealed inefficient DNA-B replication for the pseudorecombinants, and differences in viral replication properties in the two N. tabacum cell lines.