Eldene Eyssell and Elisabeth Lickindorf A Stellenbosch team has found a fast, accurate test for the fungus known as “black goo” which has been devastating the world’s vineyards. Slow to grow, the deadly fungus (Phaeomoniella chlamydospora) is difficult to detect in its early stages. Like cholesterol that blocks arteries in humans, the fungus attacks the woody tissue of grapevines, which reacts by producing a thick, sticky substance – the consistency and colour of Marmite – that blocks the vessels carrying water and minerals from the roots to the rest of the plant. The vines become lethargic, unproductive and off-colour. After three to seven years they die. Says plant pathologist Professor Pedro Crous of the University of Stellenbosch: “Walking through vineyards I realised what havoc this fungus was causing. I had to drop whatever else I was doing and investigate.” The fungus is ruinous for vine growers in wine-producing areas from California to South Australia. Although it can take years to develop, especially in the temperate climates of France, Italy, New Zealand and South Africa, it appears to be latent in nearly all “mother vines”. So farmers need to know that cuttings are healthy before planting them out into vineyards.
In the past it would take four weeks or more before the fungus could be positively identified under a microscope. Because other fungi superficially show similar symptoms, it’s vital to isolate the specific fungus quickly to halt further infection. Crous and his colleagues, biochemist Professor Dirk Bellstedt and postgraduate student Michelle Groenewald, have designed a groundbreaking diagnostic method in the form of DNA “fingerprinting” that can identify the fungus within 24 hours, even in young nursery vines that show no symptoms. Using minute samples from infected vines in South Africa and the Netherlands, they grew cultures of the fungus and extracted its DNA, which they then replicated many thousands of times using primers in a polymerase chain reaction amplification process. Because they do not allow the DNA of other fungi to multiply, these primers enable the identification of black goo DNA. Phaeomoniella chlamydospora – discovered and named by Crous in 1995 – is associated with, and may even make vines vulnerable to, other debili-tating diseases like esca and apoplexy. It is potentially as cataclysmic as the root-destroying aphid, phylloxera, that wiped out most of Europe’s vineyards in the 19th century. It is also causing dissent between vine suppliers and growers. Because the disease has been found on newly planted farms that have never had grapevines, let alone black goo, farmers are blaming nurseries for supplying infected material. Plant pathologists at the Nietvoorbij Institute of Viticulture and Oenology in Stellenbosch, for instance, found infected roots in about half of the newly transplanted nursery vines that they tested. Too little is known about the disease, its causes and how it is transmitted, however, to know whom to blame. “Doing research in this field is like walking a tightrope,” comments Crous, “because so much money is involved. The nurseries are adamant that the problem doesn’t lie with them; the farmers are equally adamant. We still have lots to find out, but a process of screening vines, young and old, and certifying them free of infection has now become very important.”
Farmers complain that the quality of cuttings is not what it was now that the industry is growing and nurseries are under pressure to meet increasing demand for new vines. Nurseries counter by pointing out that black goo is stress-induced – it can be caused by any combination of conditions, like careless planting in holes that are too small or too shallow, lack of water or poor drainage, nutrition deficiency, compacted or poorly prepared soil. It’s not certain what causes black goo to spread. It could be airborne, infecting vine wounds during pruning, or soilborne, attacking plants through the roots. It could be dispersed by rain and sprinklers or carried by insects. However it is spread, there is no cure. “A healthy plant has about 20 shoots,” Crous explains. “Once a plant becomes sick it produces fewer and fewer shoots, which means fewer and fewer bunches of grapes – that is why some people call it ‘slow dieback disease’. The length of time it takes for the plant to die depends on how early it becomes infected and how badly stressed it gets. “That’s why it’s so difficult to estimate the damage. You have to calculate the cost of the plants that die and also the cost of reduced production while the plants slowly sicken. The figure could run to millions of rands.” Crous envisages a certification scheme that would, within a year or so, enable nurseries to give young vines a clean bill of health: “We scientists have done the research and provided the knowledge. Now entrepreneurs need to apply DNA screening of vines commercially.” l The scientific announcement by M Groenewald, DU Bellstedt and PW Crous was published in the South African Journal of Science.
@Technology produces better wines Marianne Merten African frontiers South Africa’s use of clean and green technology in its wine industry – particularly its research into optimal yeast strains – is among the best in the world, according to the Wine Industry Network of Expertise and Technology (Winetech). And the country, ranked the sixth-largest wine producer in the world, is also pioneering an integrated production system, an environmentally friendly approach to winemaking from soil preparation to cultivation through to bottling.
Researchers monitor adherence through random sampling, followed by trouble-shooting and advice. “We are very confident of our capacity,” said Winetech executive director Jan Booysen. He said that research on yeast already ranks alongside similar projects in France and Australia, while local research on virus-resistant vines will bear fruit over the next two years. The use of technology in winemaking is part of a strategic review under Winetech’s Vision 2020 programme launched in June last year to identify problem areas, plan improvements and to take stock of natural and human resources.
Similar programmes are in place in Australia and California, which launched a combined 10-year strategy this year. The final report is due at the end of November and will be released to growers, farmers and other interested parties early next year. Indications are that South Africa can hold its own in terms of technology, but some attention needs to be paid to smooth out hiccups in product marketing. Last year South African winegrowers produced a harvest of 9,1-million hectolitres: 65% of this was used in winemaking, the rest for brandy, grape concentrate and grape spirit. About 104 000ha of land are under cultivation with about 312-million vines. About 80% of wines are still produced by cooperatives. About 4 500 primary wine producers employ 50 000 people. Winetech was established as a non-profit association two years ago with representatives of wine producers, wholesalers, the Institute of Wine Biotechnology at the University of Stellenbosch and agricultural institutes like Elsenburg Agricultural College and the Nietvoorbij Institute for Viticulture and Oenology, together with the government. One key concern is to ensure South Africa delivers the best wines with new technology and, at the same time, equips people in the industry with needed skills. A network of advisors has been established to help winegrowers with any difficulties. Five years ago another industry initiative, with the government and academia, led to the opening of the Institute of Wine Biotechnology. Research there has focused on developing cost-effective, environmentally friendly and efficient technology for the wine industry, including better yeast strains, disease-resistant vines and laboratory work on genetically modified grapevine cultivars. University of Stellenbosch lecturer in wine Loftie Ellis says the use of modern technology in the local wine industry means it remains well-placed to compete internationally. While machines are used to harvest grapes, especially on the larger estates, pruning and harvesting is mostly done by hand.
“We have the labour and it is better for the quality,” he says. While much of the research is recognised as groundbreaking, some in the wine industry are critical about the lack of integration of research into the day-to-day process of winemaking. Much is left up to individual winemakers. One Stellenbosch wine estate owner has pulled out all the stops to establish one of the country’s most high-tech, user-friendly cellars. As the Tokara wine cellar nears completion after more than a year in construction, the first wines and brandy are already in barrels and tanks. In the modern stainless steel, glass and concrete cellar, the temperature of fermenting grapes is monitored by thermometer probes linked to a PC capable of making any adjustments – which can also be made by remote control – and electronic sensors monitor carbon dioxide emissions. Grapes are hand-picked from the nearby vineyards, destalked in an imported crusher and directly dumped into one of the 80 fermentation tanks of varying sizes, including four made of French oak – imported because the local variety grows too fast and is believed to be unsuitable for barrels. The grapes are handled as little as possible to keep skins intact, in line with current winemaking thinking. All machinery is moveable. The press is mobile and can be put right underneath a fermentation tank to transfer the grapes with the help of gravity. “The idea is to have something that’s very flexible,” says production manager Gyles Webb. “It’s the best possible arrangement for quality.” Quality wines to fill the current gap in South African exports are the aim of this multimillion-rand cellar owned by Rand Merchant Bank chair GT Ferreira and estimated to produce half a million bottles a year. To date says Webb, “there is no South African wine that commands a significant price in overseas markets. There is really no international benchmark wine. “There are lots of really good wines but no spine-chilling stuff.”