Criniviruses associated with Cucurbit yellows disease in Greece and Cyprus. Criniviruses of cucurbits

Cucurbit yellow stunting disorder virus (CYSDV), Cucurbit chlorotic yellows virus (CCYV) and Beet pseudoyellows virus (BPYV) are three whitefly transmitted viruses classified whithin the genus Crinivirus of the family Closteroviridae. They cause similar yellowing symptoms in cucurbits and are responsible for high economic losses. In nature, CYSDV and CCYV are transmitted by Bemisia tabaci Gennadius, whereas BPYV by Trialeurodes vaporariorum Westwood. During 2012-2017 an extensive study was conducted in order to identify the virus species involved in interveinal leaf yellowing symptoms, leaf brittleness and plant vigor reduction of plant species of the Cucurbitaceae family in Greece and Cyprus. The study included survey of the three criniviruses incidence in the main cucurbit crops (cucumber, melon, watermelon and zucchini) and alternative hosts, identification of the whitefly species present in the two countries and molecular characterization of the virus populations. Results showed that both in the mainland and the islands of Greece, CYSDV was the most widespread virus with a percentage of 49.9%, followed by CCYV (20.3%) and BPYV (20.2%). B. tabaci complex and T. vaporariorum species occurrence was estimated at 54.5 and 45.6%, respectively. In Cyprus, CYSDV was predominant (96.7%), followed by CCYV (19.2%), which are transmitted solely by B. tabaci while no BPYV infection was detected. Approximately 15% of weed samples from 17 different species which belong in 12 botanical families were identified as hosts for one or more of these criniviruses. Finally, sequence analysis of the capsid protein gene of the crinivirus isolates revealed very low levels of genetic diversity further supporting the genetic stability of Crinivirus populations. The results of our long-lasting epidemiological study in two different countries of the eastern Mediterranean unveiled substantial changes on the relative incidence of the cucurbit infecting criniviruses and their whitefly vectors over the last fifteen years further suggesting the need for adopting novel management strategies.