South Africa Wine Research Projects 2025

2. VITICULTURE RESEARCH COMPLETED PROJECT

SELECTION OF LEAFROLL VIRUS IMMUNE RAMSEY

Pathsol GP 22-01 Prof Gerhard Pietersen, Patho Solutions Project is co-funded by SATI and Raisins SA Project completed: 2024

AIM AND INDUSTRY RELEVANCE: Grapevine leafroll-associated virus type 3 (GLRaV-3) is a significant viral pathogen impacting grapevine production globally. Although frequently found in scions, its presence in rootstocks, particularly Vitis species like Ramsey, is sporadic. The project aimed to identify, confirm, and propagate Ramsey rootstock individuals resistant to Grapevine leafroll-associated virus type 3 (GLRaV-3), thereby providing the South African grape industry with virus-resistant planting material. This involved screening field-grown Ramsey rootstocks under natural infection pressure, testing for virus presence using molecular and biological methods, and validating immune candidates through genetic and virological analyses. A total of ten Ramsey rootstock sources were established from field vines where the scions tested positive for GLRaV-3, but the rootstock suckers tested negative. These were propagated under insect-free greenhouse conditions and evaluated using PCR testing and grafting onto Cabernet franc indicator vines. Four sources induced leafroll symptoms in the indicators and tested positive for GLRaV-3, suggesting resistance along with low viral replication. In contrast, two sources, BK 10 44 and DP 85-026, consistently tested negative for GLRaV-3, exhibited no symptoms on Cabernet franc, and were confirmed virus-free through next-generation sequencing. Fingerprinting confirmed their genetic identity as Ramsey. The immune lines have been submitted for virus elimination and certification, positioning them for distribution across the industry.

SOUTH AFRICA WINE RESEARCH 2025

39