Trunk Cambium Facilitates Pre-Symptomatic and Year-Round Detection of Grapevine Red Blotch Virus Using the LAMP Assay

<h3>Abstract</h3> <h3>Background and goals</h3> This study uses trunk cambium sampling to improve detection of grapevine red blotch virus (GRBV) with the loop-mediated isothermal amplification (LAMP) assay, which can complement visual assessments and confirm GRBV infections. LAMP diagnostics of petiole tissues is optimal from harvest to dormancy and has shown poor detection of pre-symptomatic infections. Using Napa Valley vineyards, our goal was to validate a trunk sampling process to determine if LAMP assay diagnostics of cambium tissue could detect pre-symptomatic infections and detect GRBV on a year-round basis. We compared these results to LAMP assay testing of petiole tissue. We also surveyed LAMP assay users in the Napa Valley to assess practitioner experiences. <h3>Methods and key findings</h3> This is the first study to demonstrate that trunk cambium is the most sensitive tissue for identifying pre-symptomatic infections, with an incidence of 33% compared to cane (16%) and petiole (2.7%) tissues. Optimal GRBV detection in petiole tissue was limited to veraison through early senescence; GRBV was detected in trunk cambium tissue year-round (budbreak through dormancy). Seventy percent of LAMP users were testing from 600 to more than 1000 vines per year, preferring trunk sampling with the primary purpose of identifying pre-symptomatic, infected vines. <h3>Conclusions and significance</h3> Trunk cambium sampling is a new method for pre-symptomatic and year-round detection of GRBV with the LAMP assay. The grower community is adopting this strategy, and broader implementation of this approach will improve accurate estimates of GRBV incidence, leading to timely and informed management decisions to reduce the risk of spread.