Reducing fungicide in the vineyard is what led to the planting of disease-resistant grape varieties known as PIWIs at Famille Ducourt in Bordeaux. More than a decade later, technical director Jérémy Ducourt is pleased with the results. He typically sprays eight to 15 times per season for traditional varieties. For PIWIs, it drops to two to three per season.
PIWIs—an abbreviation of the German word pilzwiderstandsfähige, meaning fungus resistant—are a specific group of hybrid grape varieties primarily bred for resistance to powdery and downy mildew. They were developed in Europe to leverage the fungus-resistant genes found in non-Vitis vinifera vines and the sensory characteristics in Vitis vinifera.
Erratic weather patterns, a focus on environmental impact, and changing regulations for synthetic inputs are driving research on PIWIs. As scientific understanding increases, the benefits of PIWIs and their impact on vineyard management and commercial goals are becoming clear.
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History of PIWIs
The arrival of American vines carrying powdery and downy mildew is the well-documented mechanism by which mildew was introduced to European vineyards in the 19th century. Lacking the inherent fungal resistance of the American species, Vitis vinifera was quickly overwhelmed and devastation ensued.
In response, grape breeders began crossing the non-vinifera American vines with European vinifera vines, hoping to create fungus-resistant varieties while maintaining wine quality. Results were less than satisfactory.
In the late 20th century, pioneering work by German and Swiss grape breeders moved this effort forward and the name PIWI first appeared. Through extensive backcrossing, the foundation was laid for leveraging scientific and technological advances in the 21st century. Today, a new PIWI may contain as much as 95 percent vinifera genetic material.
Backcrossing is a technique used to build resistance into new varieties. It works by carrying out multiple crosses with a vinifera variety and a non-vinifera variety. Each successive crossing increases the percentage of vinifera in the new variety, decreases the percentage of non-vinifera, and retains the fungus-resistant trait.
Historically, the higher portion of vinifera material in PIWIs distinguished them from their North American counterparts. Scientific advances are, in part, changing that, allowing scientists greater precision in breeding grapes for local conditions. “In the northeastern United States, we have the challenge of very diverse pathogens because we’re at the center of origin for great pathogen diversity,” says Madeline Oravec, Ph.D., an assistant professor of viticulture at Cornell University. Consequently, the extensive library of fungus-resistant genes used to develop American hybrids draws heavily on non-vinifera species. While the development of new varieties with greater vinifera material is in the pipeline at Cornell, location will ultimately determine how that is expressed.
Identifying and Stacking Resistance
At the core of many scientific advances is the rapid genetic testing technology rhAmpSeq (RNase H2-dependent PCR Amplicon Sequencing). Under the U.S. initiative, VitisGen, researchers pioneered the use of rhAmpSeq for grape breeding in 2019, creating a panel of 2,000 genetic markers from multiple grapevine species.
Global implementation of rhAmpSeq has accelerated the discovery and identification of new disease-resistance genes. Now, if a new fungus-resistant gene is identified, researchers can specify the location with greater precision, moving beyond the general neighborhood of resistance to the exact location of instructions for identifying and repelling a mildew attack.
Stacking, or pyramiding, is a process scientists use to create multiple layers of protection around stronger resistance genes. “Not every resistance gene is equal,” says Dr. Oravec. Using the Run1-Rpv1 gene group as an example, which confers both powdery mildew (Run1) and downy mildew (Rpv1) resistance, “Run1 pretty much takes care of powdery mildew for us,” she says. “But we want to protect that gene, and by pyramiding with other strong resistance genes, we hope to have even better protection of that resistance gene.”
Another technique to benefit from the application of rhAmpSeq technology is marker-assisted selection (MAS), whereby newly germinated seedlings are scanned for the presence of desired genes. Typically, MAS scans for one to two genetic markers per vine. With rhAmpSeq, scanning increases to 2,000 genetic markers over 4,000 vines, reducing scan time from months to days.
PIWIs in Practice
The practical expression of these advances is a reduction of up to 80 percent in fungicide application. In the Rheingau at Kloster Eberbach, Germany’s largest state-owned winery, enologist and winemaker Kathrin Puff says this also helps with logistics. Managing spray schedules across multiple sites in Hessen, especially in a tough year, is particularly complex. Fewer spray applications with PIWIs streamlines logistics and saves money.
In Luxembourg, a 2026 study quantified the economic and environmental benefit of growing PIWIs by comparing mildew management for two traditional varieties with two PIWIs. Results showed PIWIs delivered a twofold economic saving, and up to a threefold reduction in environmental impact. The main cost savings were related to spraying, through lower chemical, fuel, and labor costs. The biggest environmental benefits were to soil ecology and in decreasing water toxicity.
Although plantings of PIWIs are on the rise in Europe, cultural ties to traditional varieties are strong. To that end, development of new PIWI varieties in France, known as ResDur (short for résistant durable) locally, is guided by regional signature. In Bordeaux, a new selection of vines developed by crossing ResDur varieties with Cabernet Franc, and repeating the process with Petit Verdot, will be planted in experimental plots over the next two years. The goal, says Philippe Darriet, Ph.D., a professor of enology and director of ISVV at Bordeaux University, is to develop new fungus-resistant, multigene hybrids while retaining a distinctive Bordeaux signature.
Germany is the current leader in terms of plantings, with 4,000 hectares of PIWI vines in 2025, accounting for four percent of the total area under vine in Germany and representing 10 percent growth from the previous year. If plantings are to continue increasing, industry events showcasing wines made using PIWIs are essential. At Rebschule Freytag, one of the largest vine nurseries in Germany, viticulturist Sam Doncaster says their most successful tastings involve commercial quantities of wine made from mature vines, with local production providing crucial validation.
This is also true for Eric Amberg, the second-generation owner of Amberg Grapevines in New York’s Finger Lakes. Demonstrating how PIWIs behave in the vineyard and showcasing the wine is one of the reasons their farm established a quarter-acre block of each variety they import. Both Doncaster and Amberg observe that, other than reduced spraying, PIWIs behave in the vineyard as vinifera does, requiring no significant change to existing vineyard practices.
Selling PIWIs
Direct-to-consumer continues to dominate sales for PIWIs, accounting for as much as 71 percent of PIWI sales in Germany. Retail accounts for just over 20 percent of sales and is likely to expand as major supermarket chains start to include PIWIs in their offering.
While sustainability is an increasingly familiar requirement throughout the supply chain, price remains paramount. Balancing these demands can be realized with PIWIs by translating the environmental and economic gains in the vineyard into competitive pricing.
Success in marketing, however, focuses on discovery and occasion. “Very few customers know about ResDur,” says Jonathan Ducourt, the sales and marketing director for Famille Ducourt. “We are still playing with the curiosity aspect to market these wines.” At Kloster Eberbach, Puff agrees. “Sometimes wine, especially for young drinkers is too complicated. If they want to drink, then they want to have fun.”
Advances in science and grape breeding have improved the quality of PIWIs available to producers, offering a compelling strategy for balancing the pressures of climate change, sustainability, and pricing. Educational events and tastings that build on this foundation will be the key to increasing acceptance of wines produced from these new varieties.
Dispatch
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Simone Madden-Grey is a writer originally from Aotearoa, New Zealand, and now living in the United Kingdom. She holds the WSET Diploma and has written for The Drinks Business, Australian & New Zealand Grapegrower & Winemaker, and Wine Industry Advisor. Visit happywinewoman.com to read more of her work.
