Characterization of grapevine fanleaf virus isolates in 'Chardonnay' vines exhibiting severe and mild symptoms in two vineyard parcels

Fanleaf degeneration is a complex viral disease of Vitis spp. that detrimentally impacts fruit yield and reduces the productive lifespan of most vineyards worldwide. In France, the main causal agent of the disease is grapevine fanleaf virus (GFLV). In the past, cross-protection was explored as a management strategy of GFLV, but results were unsatisfactory because mild virus strains negatively impacted fruit yield. In order to select new GFLV isolates with hypo-aggressive potential in vineyards in the Champagne region of France, we examined two old 'Chardonnay' parcels in the region. These two parcels were heavily infected with GFLV and encompassed vines with distinct phenotypes that were classified in three different categories: GFLV-infected vines displaying mild symptoms, GFLV-infected vines severely diseased, and asymptomatic GFLV-free vines. The infection status, phenotypes, and fruit production of vines in these three categories remained stable over the four-year study. The complete genomic coding sequence of GFLV variants was determined by high-throughput sequencing, and analyzed. Most grapevines tested were infected by multiple genetically divergent molecular variants but no specific molecular features were apparent for GFLV isolates from vines displaying mild symptoms. However, a genetic differentiation of GFLV molecular populations depending on the vineyard parcel was observed. The mild symptomatic grapevines identified during this study were established in a greenhouse to recover GFLV isolates of potential interest for cross-protection studies.