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A Technical Guide for Wine Producers
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Grapevine virologists get together
The Winetech Grapevine Virus Research Programme has been running for two years now. All stakeholders met recently for two days at the magnificent Plaisir de Merle Estate to discuss recent progress with the various research projects and to revisit the goals and approaches of the programme. Two days of frank and productive discussions were followed by "roadshows" in Worcester and Paarl, where researchers presented talks on selected topics of relevance to producers.
Second annual Grapevine Virus Workshop
In May 2001 Winetech held a Grapevine Virus Workshop to evaluate the first year of their Virus Research Programme. This meeting proved so successful that it led to the second annual Grapevine Virus Workshop at the Plaisir de Merle wine estate in early May 2002. A total of thirty two participants, comprising people from the wine industry, producers, nurserymen, as well as academics and researchers attended the first day, when researchers presented highlights of their work during the past year.
The programme has two main research aims, the first is to develop strategies to effectively manage the existing leafroll disease over the short and medium term, while longer term strategies aim to introduce virus resistance into wine grape cultivars.
Managing leafroll disease effectively
Key elements in controlling leafroll disease (or any other disease) are knowledge about the origin, magnitude and spread of the disease, and while everyone in the industry has very firm opinions about these aspects, Winetech decided to implement formal studies on these topics. Dr Gerhard Pietersen of the Agricultural Research Council's Plant Protection Research Institute (ARC-PPRI) in Pretoria is studying the distribution patterns of leafroll disease in the Western Cape. His study is based on visual symptoms in 67 mother block vineyards of the red cultivars Cabernet Sauvignon, Shiraz, Merlot and Pinotage in the Stellenbosch, Paarl, Wellington and Worcester districts. Some of the interesting observations he made were that although only 10% of the blocks were not infected, spread of the disease is not as fast as generally perceived - spread in existing vineyards is in the order of 0,5 % per annum. Three different types of spread were observed: random spread, a possible indication of infected planting material; clustering, which may be an indication of secondary spread (by any vector) within a vineyard; edge effects, indicative of infected neighbouring vineyards, and spread along a gradient, suggesting the involvement of insect vectors. Of these, secondary spread, especially along the rows of a vineyard, seems the most common. A disturbing observation by Dr Pietersen is that grapevine leafroll-associated virus 3 (GLRaV-3) is not the only virus spreading in the vineyards of the Western Cape.
Three researchers are studying insect vectors of leafroll disease and reported on their latest findings. Mr Vaughn Walton (ARC-Infruitec-Nietvoorbij) explained how results of the stem monitoring of mealy bugs can be combined with degree-day data to predict optimal spray dates for the control of mealy bugs, the primary vector of leafroll disease. He reported preliminary results on the use of mealy bug pheromones for more sensitive and reliable monitoring of the vector and alluded to the potential of pheromones in mealy bug mating disruption programmes. Ms Pia Addison (ARC-Infruitec-Nietvoorbij) explained the importance of the association between mealy bugs and ants and how the use of cover crops in the vineyard can assist with ant control. She also mentioned that new bait traps for ants will soon be evaluated. Dr Kerstin Krüger, of the ARC-PPRI, gave an overview of her project to determine the ability of alternative scale insects to act as vectors for leafroll disease. She reported that a soft scale insect with a proven ability to transmit the virus (in studies abroad), has been found locally. She also presented preliminary results on the artificial transmission of GLRaV-3 by the grapevine mealy bug.
Virus resistant grape cultivars
The establishment of virus resistance in wine grape cultivars is a slow process, even when modern technologies like genetic engineering is employed. Parallel with the development of resistance, a number of projects aim to elucidate the viruses involved in leafroll and other virus disease complexes, and to develop tools for their detection. Dr Dariusz Goszczynski (ARC-PPRI) talked about the progress he has made in trying to find the cause for Shiraz disease and reported that Grapevine Virus A (GVA) is consistently associated with the disease symptoms, but that a number of sequence variants of this virus exist. He also explained his progress with the development of an ELISA for the simultaneous detection of GVA and GVB. Ms Marike van der Merwe (ARC-PPRI) told the meeting that she now has reliable PCR-based detection assays for GLRaV-3, GVA and GVB, and that she will next attempt assays for Grapevine Rupestris Stem Pitting-associated Virus (GRSPaV) and GLRaV-1.
Dr Johan Burger (Stellenbosch University, Department of Genetics) gave an overview of the strategies that are being used to introduce virus resistance into grapevine. These include both very specific resistance, e.g. against GLRaV-3 using a gene from the virus itself, and broad-spectrum resistance, where the resistance gene originates from carnations. The most exciting project comprises a combination of these approaches, where the carnation resistance gene will only be switched on in grapevine cells upon virus infection. The first of the resistance gene constructs has been completed and is ready for transformation into grapevine.
The road ahead
The second day of the workshop was used for in-depth technical discussions among researchers and members of some of the Winetech technical committees. The aim was to critically evaluate progress with individual projects, to assess results that could be incorporated in the standard operational procedures of the Vine Improvement Association (VIA), and to confirm the focus areas of the research programme. The participants were satisfied with the status of the majority of projects, although recommendations of slight direction changes were made for a few projects. The general strategy to implement disease management measures for the existing situation, and the incorporation of virus resistance in the longer term, was confirmed by all present.
Grapevine Virus Roadshows
Two information sessions were held in collaboration with the VinPro consultants in Worcester and Paarl. During these sessions researchers reported on their progress with special emphasis on issues relevant to producers. The programme included an introduction to the recently launched "Leafroll Overview" by Ms Roleen Carstens. This glossy brochure explains all aspects of leafroll disease and can be obtained from Winetech (Anel Andrag Tel: 021-8073387). Mr Vaughn Walton talked about the latest developments with mealy bug research and elaborated on the use of pheromones to assist in monitoring the insects as well as the potential use in mating disruption programmes. The lively response to his talk was a clear indication that mealy bug control is an important aspect for most producers. Dr Pietersen reported preliminary results from his disease distribution survey and gave a few simple practical hints that may be incorporated in the SOPs of the VIA and may prevent secondary spread in existing diseased vineyards. Mr Tobie Oosthuizen (KWV-Vititec) explained the tedious process of wine grape improvement in South Africa and Mr Attie Jonker discussed the risks and potential dangers of importing grapevine material from abroad. Mr Nico van Rensburg (Vine Improvement Association) introduced the upgrading of the standard operational procedures of the VIA. Finally, Messrs Schalk du Toit and Dricus van der Westhuizen discussed the responsibilities of producers to manage the disease in infected vineyards. Most of these measures involve control of the insect vectors, information about these aspects is summarised in a colour brochure that is available from Winetech (Anel Andrag Tel: (021) 807-3387).
Comments from academic referees and representatives from industry alike were very positive about the research programme and its progress. Both the virus workshop and roadshows were highly successful and will feature on the Winetech calendar in future.
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Johan Burger, Dept of Genetics, US
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