Thriving on the vine

The misty days of autumn...the grape harvest is upon us, as are INRAE’s annual research awards. In Colmar and Bordeaux, members of the "grapevine resistance” team are getting a bit misty-eyed themselves over their recently acquired laurels. Theirs is the story of scientists who are harvesting the fruit of long-term research on disease-resistant grapes.

Success with deep roots

Downy mildew (Plasmopara viticola) and powdery mildew (Erysiphe necator) are serious plant diseases. In the 20th century, they were largely fought using pesticides and, to a lesser degree, genetic improvements. In the early 21st century, INRAE launched an ambitious grapevine breeding programme: INRAE-ResDur. The current challenge is to develop new varieties with high-quality berries that are also resistant to both mildews. It is necessary to produce excellent wines while simultaneously reducing pesticide treatments.

A genetics-based breakthrough innovation

Researchers are mixing and matching several pathogen-specific resistance factors and sources of resistance within individual grape varieties. France’s resistant lineages were created by INRAE researcher Alain Bouquet and his colleagues in the mid-1970s. They utilised Vitis rotundifolia, a North American species, as their starting point. In Germany, other lineages were derived from interspecific hybrids that combined cultivated grapevines with wild North American and Asian Vitis species.

The "grapevine resistance” team is taking this foundational work in several different directions. One axis is identifying and characterising the genetic factors that confer resistance to both mildews. Another is developing genetic markers for recognising individuals that carry such factors during the seedling stage. Indeed, the first phase of breeding focuses on selecting candidate varieties, which means researchers must have marker-based tools to sort through the populations produced by genetic crosses. The team is also creating bioassays for identifying resistance factors, designing new research facilities (e.g., greenhouses, growth chambers) that will facilitate its plant analyses, and further describing the genetic diversity of the pathogens that cause downy and powdery mildew.

The team’s discoveries form the basis for intermediate and final breeding of candidate varieties under production conditions. INRAE experimental units take responsibility for the intermediate breeding phase, and the team’s regional partners perform the final breeding phase, under the leadership of the French Wine and Vine Institute (IFV). During each phase, researchers evaluate grape and wine quality as well as resistance to disease (e.g., downy mildew, powdery mildew, and others) and pests. Then, the scientists seek to register the top candidates in the French variety catalogue; acceptance allows commercialisation.

Between 2000 and 2014, three sets of crossing experiments were performed. They have resulted in nine resistant grape varieties being registered in the French catalogue.

Evaluating disease resistance and variety quality under production conditions

Established in 2011 at the Grande Ferrade winery in Bordeaux, the ResIntBio experimental site has been comparing disease-resistant winegrowing systems (i.e., grapes that are resistant to both mildews) with conventional and organic winegrowing systems. The objective is to explore system functionality and to compare agricultural, economic, and environmental performance. ResIntBio research has shown that using INRAE’s resistant grape varieties can reduce mean treatment frequency index (TFI) values by more than 90% compared to regional standards. In 2017, INRAE and IFV launched the French National Observatory for the Deployment of Resistant Grape Varieties (OSCAR) with the goal of collecting and sharing information on the dynamics of downy and powdery mildew populations. OSCAR also seeks to uncover emerging health issues and inform the development of adapted viticulture systems. This collaborative network has linked INRAE with 34 different partners from IFV, various chambers of agriculture, and a number of interprofessional organisations. It currently has 150 plots in production over 75 sites.

Myriad impacts

First and foremost, larger numbers of resistant grapevines mean smaller quantities of fungicides. Faced with clear societal demands, the industry must drastically reduce pesticide use to protect human health and the environment.

The creation of resistant varieties is also a major step in the right direction: towards public policies that promote global health and the adoption of strategic objectives by the vine and wine industries. Since 2020, the French government has encouraged winemakers to plant mildew-resistant varieties, including those produced by INRAE-ResDur. These efforts are part of the CEPP regulatory framework (Certificat d'économie de produits phytosanitaires). In 2013, technical regulations for cultivated grapes were adapted to take disease resistance into account during the registration process.

Disease-resistant grape varieties are now recognised under the official origin certification scheme, a privilege previously reserved for French wines and other regional products. They fall into the same official category as traditional European grape varieties (100% Vitis vinifera L.), the only ones recognised in European origin certification requirements for wines.

Just as important, the "grapevine resistance” team has changed perceptions, practices, and activities in the vine and wine industries. As Christophe Schneider states with a note of pride, "We have managed to get the entire industry to join our quest to genetically improve grapes."

A successful foundation

Grapevine resistance: the combined fruit of luck, resources, expertise, and timing

The group’s success has involved a dash of daring on top of tremendous luck, expertise, and perseverance. The "grapevine resistance” team has accepted its award with equal measures of pleasure and humility. François Delmotte says it acknowledges the group’s "long journey", while Didier Merdinoglu speaks in more precise terms, "It is the culmination of 20 years of collaborative work". Laurent Delière almost seems to walk on air as he comments, "The award is a boost that will energise our group and propel us towards new adventures". Finally, Christophe Schneider emphasises that it is a result of "a beautiful partnership". Every one of the team’s members has expressed thanks for INRAE’s continued support and resources.