Epidemiology, genetic variance, and symptomology of grapevine viruses in Canada: A metagenomic approach

Abstract

The global grape and wine industry holds plays a significant role in the Canadian economy. However, the spread of grapevine viruses is posing a serious threat to this industry. Two such viruses, Grapevine Pinot gris virus (GPGV) and Grapevine Red Blotch Virus (GRBV), have caused substantial harm in viticulture regions like Italy and the United States, and their presence in Canada has recently been confirmed. Despite this, many epidemiological aspects of these viruses in Canada remain poorly studied. This two-part project seeks to provide novel insights into the epidemiology of GPGV and GRBV. The first part focused on investigating the genomic variance of GPGV in Canada. Researchers obtained the genome of 26 GPGV isolates from the four main grape-growing regions of Canada through high throughput sequencing. Phylogenetic analysis of their genomes revealed that Canadian GPGV is closely related to GPGV isolates in the United States, but distinct from isolates in Europe and Asia. The source of GPGV in Canada was likely a recent import from France, and the majority of Canadian GPGV isolates belong to the asymptomatic clade. The second objective involved monitoring the spread of grapevine viruses by deploying 40 virus-free sentinel vines in two vineyards of different agronomic practices in the Niagara region, both heavily infected with GRBV and GPGV. After 4 months of exposure to the infected vineyards and 11 months in a controlled environment, 46% of surviving sentinel vines were infected with GPGV. No spread of GRBV was observed. GPGV spread faster in the organic vineyard (72% infection rate) compared to the conventional one (5% infection rate). A scan for alternative hosts for grapevine viruses found that all samples from floor covering and perennial plants were free of grapevine viruses, but four out of five wild grape samples harbored GPGV. These findings underscore the importance of rigorous screening of imported plant material to prevent the introduction of grapevine viruses to Canadian vineyards. To safeguard the sustainability and profitability of Canada's grape and wine industry, a reliable local source of virus-free planting material is imperative. Furthermore, vineyard managers should remain vigilant regarding wild grape, which can act as alternative reservoirs for grapevine viruses.