# First report of grapevine downy mildew strains able to overcome resistance conferred by the combination of Rpv1 and Rpv3.1 loci in southeastern France

Anne-Sophie Miclot, Rémi Pélissier, Laura Marolleau, Isabelle D. Demeaux, François Delmotte, Frédéric Fabre, Laurent Deliere

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## ► To cite this version:

Anne-Sophie Miclot, Rémi Pélissier, Laura Marolleau, Isabelle D. Demeaux, François Delmotte, et al.. First report of grapevine downy mildew strains able to overcome resistance conferred by the combination of Rpv1 and Rpv3.1 loci in southeastern France. 12. Colloque de la Société Française de Phytopathologie, May 2025, Bordeaux, France. hal-05208184

HAL Id: hal-05208184

https://hal.inrae.fr/hal-05208184v1

Submitted on 12 Aug 2025

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# First report of grapevine downy mildew strains able to overcome resistance conferred by the combination of *Rpv1* and *Rpv3.1* loci in southeastern France

Anne-Sophie Miclot<fnref n="1" />, Rémi Pelissier<fnref n="1" />, Laura Marolleau<fnref n="1" />, Isabelle Demeaux<fnref n="1" />, François Delmotte<fnref n="1" />, Frédéric Fabre<fnref n="1" /> and Laurent Delière<fnref n="2" />

* Downy mildew, caused by *Plasmopara viticola*, is one of the most destructive grapevine diseases worldwide, leading to heavy reliance on fungicides. Developing disease-resistant grapevine varieties (DRVs) offers a sustainable alternative.

* The durability of grapevine resistance is a particularly critical issue, as grapevine is a perennial crop and the varieties currently deployed in vineyards rely on a limited number of resistance genes (only five to date for downy mildew).

* The observatory OSCAR aims to monitor the evolution of virulence of grapevine downy mildew populations towards DRV5 planted in France (2800 ha).

* In 2024, three vineyard plots in southeastern France planted with disease-resistant varieties (DRVs) carrying both *Rpv1* and *Rpv3.1* resistance loci against *Plasmopara viticola* exhibited severe downy mildew symptoms under agroclimatic conditions highly conducive to disease development.

## Materials and methods

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A) Map showing the locations of the sampled vineyards (Caderousse, Ancône, and Saint-Geniès-de-Malgoirès, indicated in red), where samples were collected from Artaban plots severely affected by downy mildew. Names of the main nearby cities are shown in black for reference. B) Photograph of downy mildew symptoms observed on grapevine leaves in the field in Caderousse.

* Twenty-one downy mildew strains were single-spored isolated from infected leaves: 11 from Caderousse, 6 from Ancone, and 4 from St-Geniès-de-Malgoirès.

* In addition to these 21 strains, we inoculated 10 reference strains with known virulence profiles: 5 virulent strains (avir), 2 virulent on *Rpv3.1* (vir3,1), 1 virulent on both *Rpv3.1* and *Rpv10* (vir3.1, 10), 1 virulent on *Rpv3.1* and *Rpv12* (vir3.1, 12), and 1 virulent on *Rpv1*, *Rpv3.1*, and *Rpv10* (vir1, 10).

* Each strains was inoculated on four leaf discs from two susceptible varieties Chardonnay and Cabernet sauvignon and six DRV5 carrying different resistance loci: Coutia (*Rpv1*), Regent (*Rpv3.1*), Muscaris (*Rpv10*), Fleurtai (*Rpv12*), Artaban and Floreal (*Rpv1* and *Rpv3.1*) and Sirano (*Rpv1* and *Rpv10*).

* Six days after inoculation, all leaf discs were photographed and the sporulation area per disk was determined by image analysis. Leaf necrosis was determined visually using the Hypersensitive Response (HR) intensity scales.

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Necrosis visual scale used to assess Hypersensitive Response (HR) to *Plasmopara viticola* infection on grapevine leaf discs that were spray-inoculated. On the top of the figure is displayed the classification of the different values of the scale according to the absence (no HR) or presence of HR (HR).

## Sporulation rate

By comparing the sporulation rate and necrosis score of the 21 tested strains with those of the reference virulent strains, the results showed that one strain was avirulent, while 20 were able to overcome the *Rpv3.1* resistance locus. Among these 20 strains, four were also able to overcome the *Rpv1* resistance locus (highlighted in red on the heatmap). A strain was considered vir1 if no necrosis was observed on any of the leaf discs of Artaban, Floreal, or Coutia inoculated with that strain. Virulent strains exhibited similar or even higher sporulation rates on resistant varieties compared to susceptible controls.

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## Necrosis score

## Conclusions

* Four out of 21 tested strains were able to overcome both *Rpv1* and *Rpv3.1* resistance loci.

* Among the three geographically distant sites, two harbored vir1 strains, suggesting two independent emergence events of virulence against *Rpv1*.

* Adaptation to *Rpv1* appears to be a local event, likely occurring at the vineyard level and the presence of virulent strains is not widespread across the vineyard regions.

* These events remain rare, considering that *Rpv1*-carrying varieties are currently planted on 1 400 ha across French vineyards.

* These breakdowns occurred under agronomic and climatic conditions highly favorable to downy mildew development.

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<footnote n="1">¹ INRAE, Bordeaux Sciences Agro, SAVE, ISVV, F-33140 Villenave d'Ornon, France</footnote>

<footnote n="2">² INRAE, Bordeaux Sciences Agro, SAVE, UE Vigne Bordeaux, ISVV, F-3882, Villenave d'Ornon, France</footnote>