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Preliminary Study of Grapevine Virus Incidence and Severity in North Carolina Muscadine Vineyards.

By: Kimberly Heagy, Christie Almeyda, Chunying Li, Mark Hoffmann

A muscadine virus survey was conducted in 2024 to assess the incidence of grapevine viruses across North Carolina (NC). This was a continuation of prior research in 2018-2020 on bunch grapes which confirmed the presence of grapevine viruses within NC vineyards. For this survey, muscadine vines were tested for grapevine leafroll associated virus complex (GLRaV-2, 3, 4, 7), grapevine red blotch virus (GRBV), grapevine virus A and B (GVA and GVB), grapevine rupetsris stem pitting-associated virus (GRSPaV), tomato ringspot virus (TRSV), and grapevine Syrah virus-1 (GSyV-1). Leaf-petiole samples were collected from 270 asymptomatic vines sampled across 8 vineyards. Samples were collected using a sterile technique with gloved hands and ethanol solution and evaluated at the NC State Micropropagation Unit. RNA was extracted from samples and then evaluated for viruses using Rt qPCR assays. The results show 37.1% incidence of GLRaV-2, 25.7% of GVB, 2.4% incidence of Xylella fastidiosa, and 0.5% incidence of GSyV-1. The total virus incidence was a 42.3% (89 vines) with co-infection incidence of 22.9% (48 vines). Additional muscadine testing will continue to understand the implication of muscadines viruses to both muscadines and bunch grapes crops.