New Study Questions Grape Breeding’s Resistance Strategy

New research is challenging a common assumption in grape breeding: that stacking multiple resistance genes always gives vines stronger protection against downy mildew. The finding matters for Italy’s wine sector and for breeding programs across Europe, where growers and researchers have pushed for varieties that can better withstand disease while reducing the need for fungicide treatments.

The report, published by VVQ - Vigne, Vini & Qualità, says that not all combinations of genes linked to resistance against downy mildew produce the same result. In some cases, adding more resistance genes does not automatically improve the vine’s defense. That raises questions for breeders who have relied on gene pyramiding, the practice of combining several resistance traits in one variety to make it harder for pathogens to break through.

Downy mildew remains one of the most damaging diseases in vineyards. It can spread quickly in wet conditions and force growers to make repeated spray applications during the season. For that reason, resistant varieties have become an important tool in efforts to cut chemical use, lower costs and reduce environmental pressure. But the new evidence suggests that the genetic strategy behind those varieties may be more complicated than expected.

The article indicates that researchers are looking more closely at how different resistance genes interact with one another. Some combinations may work well together, while others may not add much protection beyond what a single gene already provides. That means breeders cannot assume that more genes will always mean better field performance.

For winegrowers, the issue is practical as well as scientific. If a new variety is promoted as resistant but its genetic makeup does not deliver the expected level of protection, growers could face unexpected disease pressure and still need to rely on treatments. That would weaken one of the main arguments for planting resistant vines in the first place.

The findings also come at a time when European agriculture is under pressure to reduce pesticide use without sacrificing crop quality or yield. In viticulture, that balance has made disease-resistant varieties a major focus of research institutions and private breeding programs. The new evidence suggests those programs may need to refine how they select parent material and evaluate resistance before releasing new cultivars.

VVQ’s report points to a broader lesson in plant genetics: resistance is not just a matter of counting genes. The way those genes behave together, and how they perform under real vineyard conditions, can matter just as much as their number.