Comparative Diagnosis of Grapevine Red Blotch Disease by Endpoint PCR, qPCR, LAMP, and Visual Symptoms

Abstract

Background and goals

Grapevine red blotch disease (GRBD) is caused by grapevine red blotch virus (GRBV). GRBD diagnosis is often challenging because of the nature of symptoms in grapevines and complexity of testing methods. In 2020 and 2021, we compared the accuracy of four GRBV detection methods using samples collected from a commercial vineyard in southern Oregon.

Methods and key findings

Tissue samples were collected at fruit set, veraison, harvest, and dormancy from basal, middle, and apical shoot nodes of 20 GRBV-positive and negative vines. GRBD symptoms on grapevines were recorded at the time of collection, and leaf samples were tested for GRBV using loop-mediated isothermal amplification (LAMP), endpoint PCR, and quantitative PCR (qPCR). The detectability of GRBV-positive vines by the assays differed significantly among node positions, depending on phenology. At fruit set and veraison, the sensitivity of qPCR and endpoint PCR assays was 98%, whereas the sensitivity of LAMP was 49% and 78%, respectively, from basal leaf samples. At harvest and dormancy, the sensitivity of all assays was 100% in basal and middle samples, and no significant differences were detectable between LAMP, endpoint PCR, and qPCR. None of the GRBV-positive grapevine samples expressed symptoms at fruit set, and 31% of the basal canopy samples expressed symptoms at veraison. At harvest, 90% of these vines expressed symptoms, which was not significantly different than other methods. Similarly, at fruit set, the specificity of LAMP was less than 75%, whereas at veraison and harvest, it increased to 100% for all DNA-based detection methods.

Conclusions and significance

The results of this study show that PCR-based assays are the most accurate option if early diagnosis is needed; less expensive methods such as LAMP and basal canopy symptoms are reliable at later phenological stages. These findings contribute to the better understanding of GRBV detection and benefit other researchers, winegrape, and nursery industries.