This way for better wine, says UP plant virologist

Posted on April 29, 2015

Every year around autumn people marvel at the sight of acres and acres of bright red vineyards decorating the landscape of the Cape Winelands. What most of them don’t know, however, is that the red coloration of the leaves has nothing to do with autumn, but is in fact a symptom of a disease that has plagued grapevines and winemakers for centuries.

Grapevine leafroll disease affects vineyards globally, decreases the yield and quality of affected grapevines significantly, and has long been considered a devastating but insurmountable recurring hindrance.

Prof Gerhard Pietersen, a plant virologist from the University of Pretoria’s Forestry and Agricultural Biotechnology Institute (FABI), with a joint appointment at the ARC-Plant Protection Research Institute (ARC-PPRI), has changed all that.

“Because it becomes most visible during autumn, and because the virus has been with us since the very beginning of agriculture, people have simply come to accept the red grapevines and vineyards as a consequence of the changing seasons,” says Pietersen.

His research on grapevine leafroll disease is quite literally changing the face of the world’s grape and wine industries. “The reality is that leafroll disease affects every aspect of a vineyard, causing lower yields, weaker grape colours and flavours. It also causes grapes to ripen unevenly, making it difficult for winemakers to harvest at just the right time.”

Pietersen says the fact that he functions as an academic outside of the wine industry itself was precisely what gave him an advantage, because he was able to do an objective epidemiological study of the disease; he didn’t look at it as a wine problem, but rather like any other plant virus.

“What we saw was that grapevine leafroll disease actually spreads very slowly compared to other plant viruses, which makes it possible to control the disease simply by using proper prevention and management strategies,” says Pietersen. “We were able to determine that if you notice a sick plant in a healthy vineyard, removing only that plant and treating the surrounding plants with a systemic insecticide is enough to prevent any further spread. By being vigilant, leafroll can be stopped long before it infects a whole vineyard.”

Thanks largely to Pietersen’s method, South Africa has become the first country able to produce wine from totally disease-free vineyards.

The first wine farm that has taken full advantage of Pietersen’s research is the Vergelegen Wine Estate in Somerset West. Because of the vast improvement in the quality of their grape yields, some of their wines now sell for around R1000 a bottle.

The research has also already attracted tremendous interest from abroad. For the last couple of years the New Zealand Wine Industry has flown Pietersen in for regular consultations in that country. As a result, an appellation within New Zealand’s Hawks Bay wine district is almost leafroll-free. Pietersen has also been invited for talks in Israel’s Golan Heights wine district and Napa Valley in the US.

For his research efforts in helping to control and potentially eradicate grapevine leafroll disease, Pietersen was recognized as one of the University’s Academic Achiever during a gala event this month. He is rated as a grade C1 researcher by the National Research Foundation and was recently inducted as a Fellow of the South African Society for Plant Pathology.

His research grading also recognized Pietersen’s efforts in developing a new technique, using next generation DNA sequencing, to better classify populations of different strains of the Tristeza virus (which affects citrus trees). This makes it easier to identify the correct mild strains with which to inoculate trees in specific areas.

Tragically however, Pietersen says South African wine farmers have been far slower than their New Zealand counterparts in adopting methods to control leafroll disease in their vineyards. “I think it’s because the South African wine industry is old and traditional. There is a bit of a resistance to change and new methods. Which is a shame, because we have shown that the methods work and that vineyards can be completely free from this disease,” says Pietersen.

“The sooner more wine farmers start employing these methods, the sooner we can all enjoy even better wine.”

- Author Department of University Relations

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