Epidemiological Survey of Grapevine Leafroll-Associated Virus 1 and 3 in Sicily (Italy): Genetic Structure and Molecular Variability.

Background: the most widely distributed and virulent Grapevine leafroll-associated viruses(GLRaV) that affect grapevine are GLRaV-1 and GLRaV-3, transmitted semi-persistently by differentmealybugs and soft scales, mainly causing downward rolling of the leaf margins and interveinalreddening. Methods: the main objectives of this study were to investigate the genetic structureand molecular diversity of GLRaV-1 and GLRaV-3 in 617 samples from 11 autochthonous Siciliangrapevine cultivars, ascertaining their presence and spread. The detection was implemented by serologicaland molecular analyses and subsequently phylogenetic analyses on selected Sicilian isolateswere conducted. Results: in total, 33 and 138 samples resulted positive to GLRaV-1 and GLRaV-3,with an incidence of 5.34% and 22.36%, respectively; 9 out of the 11 cultivars resulted positive,while the presence of both viruses was not found in 'Grillo' and 'Moscato' cultivars. Conclusions:phylogenetic analyses of the coat protein (CP) gene of 12 GLRaV-1 selected sequences showed a closerelationship with European isolates; the discrete nucleotide differentiation and positive selectioncould demonstrate a current increase in population fitness. The phylogenetic analyses of the CP geneof 31 GLRaV-3 Sicilian CP sequences demonstrates a close relationship between Sicilian and differentcountries isolates; a certain stability of GLRaV-3 in the different cultivars analyzed is suggested bythe discrete differentiation nucleotide and negative selection of the Sicilian isolates.