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Viral infections cause the reduction of yields and efficiency of vine cultivation in all viticultural regions of the world. Simultaneous infecting with several viruses, the so-called mixed infection, can significantly increase the severity of symptoms. The article presents the results of study of mixed infecting of grapevine with viruses in the vineyards of the Crimean Peninsula during 2011-2020. More than 800 grapevine samples of 153 varieties selected in 23 vineyards of the Crimea were analyzed over the entire period of study. Presence of phytopathogenic viruses in the samples was determined by RT-PCR using virus specific primers. The share of 25.5 % of all the samples tested gave positive result for one or more of the following viruses: GFLV, GLRaV-1, GLRV-2, GLRaV-3, GFkV, GVA, GRSPaV, ArMV, GFLV. During the process of studyno vines affected by GVB virus were identified. Single-agent infection was found in 20% of the examined vines. The amount of vines affected by mixed infection was 5.48 % of all tested. In a mixed viral infection more common combinations are: GRSPaV/GFkV; GVA/GRSPaV; GVA/GLRaV-1/GRSPaV; GVA/GLRaV-3/GRSPaV. Vines were infected the most with GRSPaV and GFkV viruses, which is visually manifested in the form of mosaic leaf variegation, leaf chlorosis and the appearance of necrotic spots.

Leaf-feeding phylloxera decreases the photosynthetic activity of a grape plant, leading to decreasing number of fruit buds. In addition, phylloxera larvae emerging from the leaf galls may colonize the roots, negatively affecting the growth of the grape plant. In this study, we evaluated host tolerance of three grapevine hybrid populations obtained from crossing of the same maternal grapevine M. no. 31-77-10 with interspecific hybrids carrying introgressions from Muscadinia and other North American Vitis species against leaf-feeding grape phylloxera. Combining genotyping data of the populations obtained with 12,734 SNPs and their resistance phenotypes evaluated in the laboratory experiment, we performed an association study. As the result of GWAS, nine SNPs with the lowest significant p-values were discovered in the whole sample of 139 hybrids as associated with variation of the scores 'the percentage of infested leaves' and 'intensity of gall formation'. Three of the SNPs on LG 7 were located in the same chromosome interval where a major QTL (RDV6) for root phylloxera resistance was reported from Muscadine background. Two SNPs on LG 8 were detected within the gene, encoding E3 ubiquitin-protein ligase UPL4 involved in apoptosis. SNPs detected on LG 13 and LG 18 may overlap with the previously reported QTLs for phylloxera resistance inherited from V. cinerea. [ABSTRACT FROM AUTHOR]