South Africa Wine Research Projects

2. VITICULTURE RESEARCH PROJECT IN PROGRESS

SELECTION OF LEAFROLL VIRUS IMMUNE RAMSEY

Pathsol GP 22-01 Prof Gerhard Pietersen, Patho Solutions Project is co-funded by SATI and Raisins SA Start date: 2022

AIM AND INDUSTRY RELEVANCE: Using Ramsey ( Vitis champini , formerly Salt creek), researchers aim to identify grapevine leafroll associated virus type 3 (GLRaV-3) immune and GLRaV-3 tolerant individuals of this rootstock. They will then establish these two phenotypes, make them available to industry and determine whether genetic differences, based initially on standard molecular markers, exist between those individuals. In previous Winetech-funded projects, researchers have shown that (GLRaV-3) is only detected in some individuals of Vitis rootstock crosses and species commonly used in South Africa. This was tested under conditions where the corresponding scion tested positive for the virus. Researchers have concluded that rootstock crosses, generally made from Vitis species other than Vitis vinifera , have resistance to GLRaV-3 infection but that these crosses are heterogeneous regarding this trait. Researchers will determine whether the difference between immune (no virus replication) and tolerant (virus replication but no symptoms) Ramsey individuals can be genetically identified with standard markers as a first step towards identifying the gene(s) that differ between the two phenotypes. Identifying such genes will allow the exploitation of these in future leafroll control strategies using vines which do not allow GLRaV-3 replication. If successful, the industry can be provided with a Ramsey clone, immune to GLRaV-3 infection, of known virus status, for use as a rootstock. This obviates the need to test for GLRaV-3 infection within the certification scheme and will prevent the potential transmission route of this virus via rootstocks. This will obviate the need for fallow periods between vineyards where this rootstock is used as rootstock volunteers will not contain the virus. Ramsey is selected as the first of all rootstock c ultivars to which this will be done, as it is a very widely utilised rootstock for both table and wine grapes and was requested to do so by the Winetech Plant Improvement Subcommittee.

SOUTH AFRICA WINE RESEARCH 2024

39