South Africa Wine Research Projects 2025

2. VITICULTURE RESEARCH COMPLETED PROJECT

DETERMINATION OF CULTIVARS AMENABLE TO VISUAL ASSESSMENT FOR LEAFROLL EVALUATION

Pathsol GP 22-02 Prof Gerhard Pietersen, Patho Solutions Project completed: 2024

AIM AND INDUSTRY RELEVANCE: Grapevine leafroll disease, primarily caused by GLRaV-3, poses a significant challenge to certifying grapevine planting material. Although ELISA testing is the standard method for detecting the virus, it is limited to a specific seasonal window and demands substantial resources. This project aimed to ascertain whether visual assessment of leafroll symptoms in specific red grape cultivars—Durif, Malbec, Pinot Noir, Pinotage, and Ruby Cabernet—can reliably replace ELISA testing as the method for identifying grapevine leafroll disease. Over three growing seasons, the study evaluated the reliability of visual diagnosis of grapevine leafroll by comparing symptoms with ELISA test results for GLRaV-3 across 15 vineyards. The results demonstrated a consistently high negative predictive value (NPV) across all cultivars and regions, indicating that visually healthy vines could be free of the virus. Visual assessments proved particularly accurate in low-infection vineyards, typical of certified mother blocks, suggesting that ELISA testing can be confidently substituted with visual inspection under these circumstances. Although some false positives arose due to latent infections or testing limitations, these were generally explicable and did not compromise the overall reliability of visual assessment. Cultivars varied slightly in symptom clarity, with Pinotage exhibiting the most distinct leafroll signs and Ruby Cabernet necessitating experienced evaluators. The study concludes that trained personnel can reliably utilise visual assessments instead of ELISA for these cultivars, allowing testing resources to be redirected toward white cultivars, where visual detection is not feasible.

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SOUTH AFRICA WINE RESEARCH 2025