A diverse virome of leafroll-infected grapevine unveiled by dsRNA sequencing

Quebec is the third-largest wine grape producing province in Canada, and the industry is constantly expanding. Traditionally, 90% of the grapevine cultivars grown in Quebec were winter hardy and largely dominated by interspecific hybrid Vitis sp. cultivars. Over the years, the winter protection techniques adopted by growers and climate changes have offered an opportunity to establish V. vinifera L. cultivars (e.g., Pinot noir). We characterized the virome of leafroll-infected interspecific hybrid cultivar and compared it to the virome of V. vinifera cultivar to support and facilitate the transition of the industry. This study highlights the complexity of the grapevine virome associated with leafroll-infected plants of different cultivars. Independently of the grapevine cultivar, the plants were infected by multiple viral and viroid species and different variants of the same virus. These results are supported by Beuve et al. However, these authors described this complex virome only on the cultivar Pinot noir. The symptomless hybrid cultivar Vidal presents a complex virome which, in contrast, was dominated by grapevine Rupestris stem pitting-associated virus despite the presence of grapevine leafroll disease (GLD) virus species. Therefore, removing and destroying of symptomatic grapevines and possibly vines immediately adjacent to those symptomatic grapevines, which is proven to be efficient to control GLD spread, will not be effective in vineyards where Vidal grapevines are grown because this latter cultivar will hamper the management efforts. During the transition and establishment of new and less winter hardy cultivars such as Vitis vinifera (e.g., Pinot noir) in Quebec, growers cannot rely only on certified material derived from virus-tested stocks, they also need to periodically test their vineyards for at least the presence of GLRaV (2 and 3), and the testing should particularly include the symptomless Vidal cultivar. These findings and their implications for grapevine leafroll disease management are discussed.