Protecting Wine Grapes from Mildew

Both Australia and Germany have large wine growing industries which are important both culturally and economically. As such, diseases which effects grapes and grapevines can be a costly problem.

For example, with an estimated cost to the Australian industry of approximately A$140 million per annum, powdery mildew (a fungal disease which affects a wide range of plants, including apples, peas and roses) and downy mildew (an oomycete pathogen that is a particular problem on grapes and cucurbit vegetables, such as cucumber and pumpkin) are the most economically significant diseases in viticulture, causing reduced yield and loss of berry and wine quality.

CSIRO has working on solutions to these two diseases, in particular, they have been searching for genetics which are resistant to the pathogens which cause powdery and downy mildew.

The cultivated grapevine, Vitis vinifera, has no natural genetic resistance to powdery or downy mildew. This is due to the two organisms evolving on different continents. Vitis vinifera first evolved in Europe while the pathogens came from North America. For this reason, the only method growers have to control these pathogens is by using fungicides.

Interestingly, it is grapevines that are responsible for the bulk of fungicide use in agriculture. In 2002, for example, grapevines accounted for approximately 6 per cent of the total crop area in Europe, however, of all fungicides used, around 70 per cent were applied to grapevines. Since then, Europe has been working towards reducing its fungicide use. The Australian industry is also attempting to do the same, therefore ensuring a more sustainable wine industry and continued exports to Europe.

The CSIRO, in collaboration with the National Institute for Agronomic Research (INRA), in France, have been able to identify seven individual resistance gene candidates which were tested using gene technology to determine whether they conferred resistance to powdery or downy mildew. Each gene was introduced into several grapevine varieties including Shiraz, Tempranillo, Cariganan and Portan which were then tested for resistance.

The experiment revealed two resistance genes, one for powdery mildew and another with resistance to downy mildew. There are two methods in which these genes can be utilised. Firstly, genetically-enhanced disease-resistant versions of existing premium varieties like Shiraz could be produced through genetic transformation. While Australian and world acceptance of genetically modified grapevines is most likely to be some time away, this method would provide protection against these important pathogens without the negative impacts on wine quality associated with traditional breeding techniques.

The second option uses the knowledge of these genes to create DNA markers for application in marker-assisted breeding. Rather than directly manipulating the plant’s DNA, marker-assisted breeding uses DNA markers to identify specific traits in the plant at the seedling stage. This dramatically reduces the time required to identify varieties which express the desired trait, in this case resistance, in a breeding program.

Photo credit: http://www.colourbox.com. Material used in the preparation of this article has been drawn from CSIRO.

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