when humid conditions put a damper on grape-growing season — as happened, for example, during the 2010 vintage in Sonoma County, Calif. — wine-grape vines, especially close-clustered varieties like pinot noir and zinfandel, are prone to the development of a fast-spreading, foul-looking white glaze. The condition, known as powdery mildew, creates a host of health problems for vines. Most destructively, it renders affected grapes unsuitable for their raison d’être — making fine wine.
Viticulturists employ a number of tactics to combat losses related to the condition. One is the management of vines’ leafy canopies — trimming back growth over-spreading the vines to reduce the humidity within. Another is the application of fungicides.
Here in Missouri, however, powdery mildew is hardly a problem for our signature wine grape, Norton — this despite a climate that would seem a spore’s best friend.
“The warm, humid environment of Missouri is perfect for the growth of fungal pathogens, such as mildew. Yet Norton resists the fungus,” says Walter Gassmann, an associate professor of plant sciences at MU. The reason, he adds, is that Norton boasts a robust genetic defense.
Gassmann’s recent research has shown that Norton, a cultivar derived from the native Vitis aestivalis, is resistant because it is quicker to develop a particular fungus-fighting protein than the famous wine grapes from the Old World’s Vitis vinifera varieties.
Gassmann, working with Wenping Qiu, professor and director of the Center for Grapevine Biotechnology at Missouri State University, made the discovery by building on previous research showing that a gene containing the blueprint for the fungus-fighting protein is present in both Norton and European-derived grape varieties. Gassmann and Qiu added the gene to the model plant Arabidopsis, eventually confirming that it did indeed confer defense against mildew.
The next step, the researchers say, is to learn why the genetic instructions in Norton give its proteins a leg up on those of its European cousins. Such a discovery could pave the way to a transgenic solution to vinifera’s mildew problem, but Gassmann cautions that no breakthrough is imminent. Even if it were, he adds, it’s unlikely that today’s connoisseurs are ready to swirl, swish and spit a transgenic Gevrey-Chambertin. That’s too bad, he says, because “the alternative to transgenic technology is breeding, which takes a very long time and changes the quality of the grape. Until then, there really is no way to eliminate fungicide use.”
Gassmann and Qiu’s study was recently published in the plant sciences journal Planta. It was funded in part by a grant from the U.S. Department of Agriculture.