Field surveys of European wine grapes ( Vitis vinifera cultivars) were completed between 2018 and 2020 to understand the distribution and incidence of grapevine viruses in North Carolina. In October and November of 2018 to 2020, 1,620 leaf petiole samples were collected from 270 symptomatic vines across 14 vineyards in North Carolina. The petiole samples were assessed for grapevine leafroll associated virus-2, -3, -4, and -7 (GLRaV-2, -3, -4, and -7), grapevine red blotch virus (GRBV), grapevine virus A, grapevine virus B, and tobacco ringspot virus (TRSV). Samples were also tested for Xylella fastidiosa, a common bacterial pathogen in North Carolina and the causal agent of Pierce's disease. Petiole samples were collected and immediately stored on ice overnight. Total nucleic acids were extracted from petiole samples and analyzed for the presence of viruses using reverse-transcription polymerase chain reaction. Samples that crossed a C Q = 35 threshold were considered positive. More than one-third (34.8%) of evaluated samples were positive for GRBV, whereas other viruses had lower incidence: GLRaV-3 at 8.1%, GLRaV-2 at 4.8%, and TRSV at 0.3%. For the bacterium X. fastidiosa, the total field incidence was 11.5%. Seventy-four percent of the state GRBV infections were found in the Yadkin Valley, which had a regional incidence of 46.7%. GLRaV-2 and GLRaV-3 were found in just a few vineyards, with a much lower incidence across the state. This study suggests GRBV as the main grapevine virus threat for North Carolina and implies the need for further investigations on region-specific vector presence and management methods.
Heagy et al. (Thu,) studied this question.