ARI Biennial Review for 2018-2019

Grapevine viruses Grapevines are known to be infected with over 80 distinct virus species. A survey was conducted to investigate the presence of viruses in grapevine crops in Cyprus. More than 800 leaf samples from red and white varieties were randomly collected from the districts of Lemesos, Pafos and Lefkosia, and total RNA was extracted. All samples were tested using serological and molecular methods for the presence of 14 viruses involved in leaf- roll-associated and rugose woody disease complex, as well as fleck, infectious degeneration and decline disease complex. Results showed that among the viruses associated to leaf-roll disease, Grapevine leafroll-associated virus 3 (GLRaV-3) was detected in more than 40% of the samples tested, followed by GLRaV-1 (6%) and GLRaV- 2 (1%). The incidence of viruses involved in rugose woody complex was 14, 5 and 2% for Grapevine virus A (GVA), Grapevine rupestris stem pitting-associate virus (GRSPaV) and Grapevine virus B (GVB), respectively. Grapevine fanleaf virus (GFLV) and Grapevine fleck virus (GFkV) were also detected at 8 and 0.5% respectively. Two new viruses, Grapevine roditis leaf discoloration associated virus (GRLDaV) and Grapevine pinot gris virus (GPGV) were identified in a selection of samples from Greek and other imported varieties. Finally, Arabis mosaic virus (ArMV), Tomato ringspot virus (ToRSV), and the grapevine leaf-roll-associated viruses 4 and 7, were not detected. Interestingly, most viruses were detected in mixed infections of various combinations. The presence of these viruses has most likely resulted from the use of infected plant material combined with possible spread by vectors. (L.C. Papayiannis) Epidemiological studies of whitefly-transmitted viruses in Cyprus During the past twenty years, an extensive study has been conducted in order to assess the identity and prevalence of whitefly transmitted viruses and their vectors in major vegetable crops of Cyprus, using molecular- based diagnostic tools. Results showed that TYLCV (IS and MLD) is the only Begomovirus species involved in tomato yellow leaf curl disease epidemics and is widely distributed. TYLCV was also detected in 50 different weed species belonging to 15 botanical families, which could serve as natural virus reservoirs. Three Crinivirus species have been identified and associated with yellowing symptoms. In cucurbits, CYSDV is the predominant virus (95%) infecting cucumber, melon, watermelon and zucchini crops, followed by CCYV (20%), which has recently emerged and established as a new pathogen in Cyprus, and in most cases is detected in mixed infections with CYSDV. In tomato crops, ToCV is identified in plants showing chlorotic symptoms with a low incidence (2%). Finally, the ipomovirus CVYV is rarely detected in greenhouse cucumbers with symptoms of vein clearing (0.2%). In nature, all of these viruses are transmitted with Bemisia tabaci MEAM1 (also known as biotype B), which is currently the most abound and important whitefly vector in Cyprus. This high incidence and distribution of whitefly-transmitted viruses in vegetable crops and weeds, requires the adoption of new management strategies that should focus on the use of resistant or tolerant hybrids when available, removal of alternative virus hosts and more effective control of whitefly vectors. (L.C. Papayiannis) 45 PLANT PROTECTION