A severe strain of Cucumber mosaic virus (CMV) originating from an infected tomato plant (GastouniOlympia, Greece) was isolated in tobacco (Nicotiana tabacum cv. Xanthi nc), after three serial local lesion passages in Chenopodium quinoa and designated CMV-G. CMV-G induces yellow mosaic (YM) symptoms in tobacco. When CMV-G was passed mechanically through C. quinoa, phenotypic variants inducing YM or green mild mosaic (MM) in tobacco were isolated. Aphid transmission, from different hosts, appears to be an effective approach for separating MM variants of CMV-G from YM variants. In particular, aphid transmission from zucchini proved to be very efficient in selecting for MM variants. In contrast, aphids transmitted only YM variants from tomato plants. Molecular characterization of CMV-G and its progeny resulted in their classification in the CMV subgroup IB, free of satellite RNA, being the first discovery of the subgroup IB in Greece. In the Solanaceae family (tobacco, tomato, pepper) YM variants induced more severe symptoms than the MM variants. YM and MM phenotype was stable in tobacco for all seven passages tried using the obtained YM and MM variants. Cross-protection experiments showed that an isolated MM variant was able to protect tobacco plants against a challenge infection by a YM variant.

Cucumber mosaic cucumovirus (CMV) has been the most serious pathogen of tomato in Greece for the last 15 years, causing tomato shrinkage, tomato necrosis and tomato fruit necrosis. In an epidemiological study in Eleia county, one of the main centres of production of processing tomato in Greece and one most affected by CMV, it was confirmed that the virus had an extremely high frequency. Disease frequency and severity was found to have a patchy spatial and temporal distribution at county, zone and locality level, during the years and within 1998, the main year of experimentation (and a disastrous year for CMV). Great variation was found in the trends of infection frequencies during the growing season of 1998 in the 15 experimental fields but all were finally 100% or almost 100% infected. The trends of infection frequency in these 15 fields paralleled total captures of alate aphids by a Rothamsted-type trap, whereas in one of these fields, with a Moericke-type trap, these parallel captures were composed almost exclusively of Aphis spiraecola.

Unusual symptoms were observed on 'Baresana' x 'Baresana' Vitis vinifera hybrid vines in the Grapevine Variety Collection of the Grapevine Institute, Athens. The affected vines showed sharp angular mosaic on leaves, along the veins and in vein angles, malformations, abortive flowers or very few berries with smaller, wrinkled and non-germinating seeds, as well as gradual decline, severe stunting and death of the vine. Serological tests on diseased vines for the presence of 13 known grapevine viruses gave negative results. An infectious agent was transmitted mechanically to several herbaceous indicator plants. Koch's Postulates were fulfilled, and the agent, proven to be a virus, was named Grapevine angular mosaic virus (GAMV). Serological tests have been developed for the virus. The most conserved polymerase region showed significant similarity of GAMV with members of subgroup 1 of the Ilarvirus genus; however ML phylogenetic analysis could not support its clustering within this subgroup. GAMV differs serologically and in particle morphology from Grapevine line pattern virus (GLPV) a putative Eur