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How Thirsty Are Your Grapes?

Grape vines in the drought-affected Orange region, Australia, 2007
© AFP/ Anoek de Groot | Grape vines in the drought-affected Orange region, Australia, 2007
North American researchers are working on an age-old quandary: when to water vines, and when to hold off.

“I’m a cab sav girl,” says Canadian scientist Dr Susan Murch with a laugh when asked what wine she likes to drink. She’s also big on roots, shoots and secondary plant metabolism – the stage in a grape’s life when all the tasty flavor compounds develop.
 
Murch, who has studied wine grapes for more than a decade, is hard at work on a project that could yield some game-changers for the world of viticulture.
 
Her team at the University of British Columbia’s Okanagan campus has received nearly US$150,000 from the Canadian Southern Interior Development Initiative Trust to move ahead with a two-pronged project started in 2005 called “Biotechnology Resources for Improving Water Use Efficiency in Vineyards.”
 
Scientists are looking for tools that will help growers to minimize their water usage and manage intentional drought for grape quality. Deciding when not to water is one of the most essential elements of growing wine grapes, but part of successfully stressing a vine is knowing when the plant has had enough and really needs a drink.
 
“There is a very delicate happy medium between not having enough stress and having too much stress,” says Murch. A lack of water means that the vines have to dig deep to find nutrients – something that is considered desirable in wine-growing because results in smaller, more intensely flavored grapes and a higher sugar content. However, if the vines get too dry, the grapes don’t ripen properly and the yield is also affected.

If the first aspect of Murch’s research is successful, growers’ anxiety around deciding just how thirsty they want to make their plants – and for how long – could be solved by a check that’s as simple as a stick-test for pregnancy. “The idea is that it will be a test kit that any grower can use with the same expertise as that required for a pregnancy-test kit,” says Murch.

Her team have done genomic studies to identify proteins that are present in the leaves of a vine that is not getting enough water. The so-called stress metabolites serve as a “bio-marker.” The latest research funding offers the chance to create a commercial, farmer-friendly version of the test that can be easily used in vineyards. Knowing vines’ stress levels will aid in avoiding unnecessary or preventive watering and help vineyards with irrigation-management strategies that promote water conservation.
 
Dr Dong Wang, a researcher for the United States Department of Agriculture, says that “on the decision-making side, it doesn’t matter how you get the water on the field, you need to know when.”

Wang works on vineyard water strategies that combine remote sensing of evaporation with satellite images, local weather data and leaf temperature to manage irrigation. He says the department, together with the University of California network, is also investigating ways to identify “strategies for when to stress” the vines, since that is one of the most crucial moments for a viticulturist.

A new irrigation system is installed in a vineyard near Calitzdorp, northeast of Cape Town
© AFP/ Rodger Bosch | A new irrigation system is installed in a vineyard near Calitzdorp, northeast of Cape Town
 
But it’s not only about when to water – it’s also about having plants that need less water in the first place. The second half of Murch’s project will involve work on developing a new collection of drought-tolerant rootstocks specifically for her local Okanagan Valley wine region, where water is in short supply.
 
The plan is to adapt existing varieties of rootstock through genetic work in the lab to create a stable of drought-tolerant options. The scientists are exploring different ways of doing that, including deeper root systems and plants’ hormonal responses to low soil moisture. Modifying rootstocks is common practice, though usually targeted at developing pest resistance. Effects on end flavors in the wine are expected to be minimal.
 
“We will also be looking at many of the potentially volatile flavor compounds as measures of the quality of the fruit and hope to find that the rootstock will support growth of a high-quality crop,” says Murch.

The common practice of grafting allows viticulturists to grow their preferred variety regardless of which rootstock they use. Murch’s prototypes, which will be organic, will be field-tested at two vineyards, including Summerhill Pyramid Winery in Kelowna, British Columbia, one of the most visited in Canada. Proprietor Stephen Cipes is excited to be part of the project. “We go around saying we want to save the planet, and if you say it, you have to do it,” he says. “We want to find ways to grow healthy plants that don’t use chemicals, and conserve water.”
 
Cipes is thinking of grafting either pinot noir onto the rootstocks if they decide to go with a red, or riesling and chardonnay if they choose a white.
 
The hope is that the new rootstocks will reduce water consumption by about 45%. Murch says her team expect that their findings will be useful to growers in drought-prone regions of Australia and California. The stocks could also prove beneficial for Old World heavyweights such as France, where irrigation for the production of wine is restricted as it’s regarded as interference with the natural conditions.

“One of the things about research,” says Murch, “is that you’re always surprised about the people who call you up and say, ‘Oh, we could use that.’”

The University of British Columbia says it expects that the rootstocks will have “strong commercialization potential and projected worldwide sales.”

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