Grapevine leafroll disease is caused by grapevine leafroll-associated viruses (GLRaVs). These viruses are common in vineyards worldwide and often associated with vitiviruses that are involved in the rugose wood complex of grapevine. Ten mealybug species are known as vectors of one or several of these grapevine viruses, including the apple mealybug Phenacoccus aceris which is widespread in Holarctic regions and able to transmit Grapevine leafroll-associated virus-1 and -3 (GLRaV-1 and -3). Our aim was to characterize the transmission features of leafroll viruses by Phenacoccus aceris in order to better understand the contribution of this mealybug to leafroll epidemics. Results showed that Phenacoccus aceris is able to transmit GLRaV-1, -3, -4, -5, -6, and -9 to grapevine but not GLRaV-7. This is the first report of GLRaV-6 transmission by a mealybug. Also, for the first time it was shown that Phenacoccus aceris could vector vitiviruses Grapevine virus A (GVA) and Grapevine virus B (GVB). First instar nymphs were the most efficient stage in transmitting GLRaV-1, -3, and GVA. This research sheds light on the transmission biology of grapevine viruses by Phenacoccus aceris and represents a step forward to leafroll disease management.

We have characterized the virome of a grapevine Pinot Noir accession (P70) that displayed, over the year, very stable and strong leafroll symptoms. For this, we have used two extraction methods (dsRNA and total RNA) coupled with the high throughput sequencing (HTS) Illumina technique. While a great disparity in viral sequences were observed, both approaches gave similar results, revealing a very complex infection status. Five virus and viroid isolates [Grapevine leafroll-associated viruse-1 (GLRaV-1), Grapevine virus A (GVA), Grapevine rupestris stem pitting-associated virus (GRSPaV), Hop stunt viroid (HSVd) and Grapevine yellow speckle viroid 1 (GYSVd1)] were detected in P70 with a grand total of eleven variants being identified and de novo assembled. A comparison between both extraction methods regarding their power to detect viruses and the ease of genome assembly is also provided.

Spread patterns of a Grapevine leafrollassociated virus 1 (GLRaV-1) epidemic and a mealybug infestation survey over 10 year were recorded in two Burgundy French vineyards to investigate the relation between them. The temporal evolution of leafroll spread at both study sites was compared on disease incidence data with logistic regression models. We first tested if the spatial distribution of the disease and the mealybug were aggregated using permutation methods, then we tested the independence between the two spatial patterns by randomly shifting one pattern. In Bon-zon, an increase from 5 % to 86 % of leafroll prevalence was observed over an 8-year time span, whereas leafroll prevalence remained stable around 5 % in Marsannay-la-Côte during the same period. In Bonzon, the disease spread rapidly from older neighbouring vineyards in four main patches while no spread of the disease was recorded from infected vines in Marsannay-la-Côte. The mealybug Phenacoccus aceris was recorded on 74 % of vines in Bonzon throughout the study and only 6 % of vines in Marsannay-la-Côte. In the latter location, the disease was not associated with the presence of the mealybug, so that it may have arisen from infected plant material escaping the sanitary inspection. In Bonzon, the significant statistical correlation between the mealybug distribution and diseased plants suggests that P. aceris was responsible for the rapid spread of GLRaV-1 in the vineyard. This is the first report of GLRaV-1 natural spread in Europe.Keywords Epidemiology . Ampelovirus . Grapevine scale insects . Leafroll disease . Spatial statistics Abbreviations GLRaVGrapevine leafroll-associated virus GVA Grapevine virus A GVB Grapevine virus B DAS-ELISA Double-antibody sandwich enzyme-linked immunosorbent assay