Grapevine Pinot gris virus: is pathogenicity related to genetic diversity

Grapevine Pinot gris virus (GPGV) is a recently characterized member of the genus Trichovirus, putatively associated to a new grapevine disease whose symptomatology consists of chlorotic mottling, stunting and deformation of the leaves. Firstly identified through high-throughput sequencing of a cv Pinot Gris accession in the Trento's area (northern Italy), GPGV was later frequently detected in vineyards of northern and southern Italy, Slovenia, South Korea, Czech Republic and Slovak Republic. Despite the high occurrence and the fast rate of natural spreading, GPGV role in the induction of mentioned aetiology is under study. With these premises, the present study aimed at further characterizing GPGV pathogenicity, starting from NGS analysis of two Pinot gris accessions, one showing symptoms of leaf mottling, the other asymptomatic. Virome profile analysis consistently duplicated what already described, unravelling the presence of GPGV together with Grapevine rupestris stem pitting virus (GRSPaV), Grapevine Rupestris vein feathering virus (GRVFV) and the two viroids Hop stunt viroid (HSVd) and Grapevine yellow speckle viroid 1 (GYSVd-1), without relevant differences between the two vines. Derived consensus sequences were therefore submitted to whole genome pairwise and phylogenetic comparison, additionally including GPGV isolates originating from Italian and Czech-Slovak vineyards. Phylogenetic reconstruction strongly clustered strains associated to symptom expression, clearly distinguished from those characterized by latent behaviour. On that account we extended the analysis to a sample population comprising grapevine accessions known to be free from viruses associated to leafroll, infectious degenerations or rugose-wood diseases and found a 84% of association of GPGV with symptoms. Maximum likelihood and Bayesian analyses were focused on two GPGV genomic regions, i.e. the RNA polymerase RNA dependent domain of the replicase gene, and a segment comprised between the movement protein and the coat protein genes. We ascertained that the lineage grouping symptomatic vines is distinct from those of symptomless plants, thus hypothesizing that an evolutionary dynamic, independent from the vine genotype, could have selected for virulent or latent GPGV strains