Occurrence of Major Grapevine Viruses in Oklahoma and Genetic Diversity Assessment of Field Isolates of Grapevine Leafroll-Associated Virus 3 and Grapevine Red Blotch Virus.

Oklahoma grapevine production interests are on the rise, but very little is known about the occurrence of major grapevine-infecting viruses in the state. To address this knowledge gap, a total of 85 grapevine samples were collected from eight vineyards across six counties in Oklahoma during the spring and fall of 2024. Total RNA extracts from each sample were assayed for 14 major viruses by RT-PCR, including grapevine leafroll-associated virus 1 (GLRaV-1), GLRaV-2, GLRaV-3, GLRaV-4, grapevine fanleaf virus (GFLV), grapevine red blotch virus (GRBV), tobacco ringspot virus, tomato ringspot virus, grapevine fleck virus, grapevine rupestris stem pitting-associated virus (GRSPaV), grapevine virus A (GVA), GVB, GVE, and GVH. Virus infection was detected in 68.2% of samples, with mixed infections (36.5%) being more common than single infections. Seven of the targeted viruses were detected at varying levels of incidences, including GRBV (48.2%), GRSPaV (40%) GLRaV-3 (20%), GFLV (11.8%), GVE (11.8%), GVA (5.9%), and GVH (2.4%). GRBV variants belonging to both clades I and II were identified in Oklahoma, with the clade II members being more predominant. Multigenic diversity assessments of GLRaV-3 isolates from Oklahoma showed the occurrence of variants belonging to both clades I and V, with the latter being more frequently detected in the state relative to results from other U.S. growing regions. The findings of the study underscore the importance of continued virus surveillance, the use of clean plant materials, and targeted management strategies to protect Oklahoma's developing vineyards from the long-term impact of viral diseases.