WHITEFLY-TRANSMITTED VIRUSES OF THE SOUTHWEST (PLANT, INSECT-TRANSMITTED GEMINIVIRUSES).

Three distinct plant viruses, transmitted by the tobacco whitefly Bemisia tabaci Genn., were associated with diseased food or fiber crops grown in the southwestern deserts of Arizona. The cotton leaf crumple virus (CLCV), thought to affect only cotton Gossypium (L.) spp., is now known to infect other malvaceous plants and members of the Convolvulaceae and Leguminosae. Results of an experimental host range study suggest that potential virus-vector reservoirs may exist in cotton growing regions which include both weeds and cultivated plants. Geminivirus-like (GVL) particles of ∼18 x 30 nm were isolated for the first time from CLCV-infected bean, Phaseolus vulgaris (L.), 'Red Kidney', a plant which was a better purification host than cotton. Studies of CLCV-vector relationships indicated that the acquisition- and inoculation-access times, latent period and length of retention by whitefly vectors were similar to those of the original isolate reported in California in 1954. When growth chamber temperatures of 26, 32, and 37C were used in virus-vector studies, optimal acquisition and transmission occurred at 32C while temperatures of 37C were lethal to whitefly adults. Two additional virus-like agents were isolated from single and mixed infections of lettuce or melons, respectively. The virus-like agent from lettuce infected primarily members of the Chenopodiaceae, Compositae and Cucurbitaceae, and was whitefly but not mechanically transmissible. Long flexuous closterovirus-like rods of ∼10 x 1400-2000 nm were visualized in extracts prepared from plants inoculated with the lettuce isolate. The isolate was similar to the lettuce infectious yellow virus (LIYV) based upon host range, transmission characteristics and unique particle morphology. Both long flexuous rods like those associated with the lettuce isolate and GVL particles of 18 x 30 nm were associated with diseased melons. The host range of the GVL agent was confined to the Cucurbitaceae and Leguminosae and the agent was separated from the mixed infection by mechanical transmission to a non-LIYV host. The GVL-agent was distinct from previously described cucurbit viruses including the squash leaf curl virus, based upon host range and transmission characteristics and was tentatively designated as the watermelon curly mottle virus (WCMV)