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Cover of Evolutionary Applications. © INRA

Vigilance in the vines: can grapevine downy mildew adapt to resistant grape varieties?

New varieties of grape, resistant to pests such as grapevine downy mildew, are appearing on the market. But little is known about a pathogen’s ability to adapt to resistant varieties. By comparing the aggressiveness of different mildew populations, INRA scientists have shown that while global resistance in grape varieties is good, mildew can adapt quickly, thus reducing the effectiveness of this resistance. Results of the study are published in Evolutionary Applications.

Updated on 06/08/2017
Published on 05/13/2016

Cultivated grape varieties are highly susceptible to air-borne diseases such as grapevine downy mildew (Plasmopara viticola). The grape variety Vitis vinifera cannot spontaneously defend itself from this disease, which was imported from America to Europe in the 19th century. Currently, the plant is protected against this pathogen by being treated five to ten times with a fungicide over the course of a growing season. An alternative method for managing disease – and one already used for many other crops –  is to use resistant grapevine varieties. Thanks to several successful grapevine improvement programmes in Europe, this solution is now a viable option in viticulture. The method could reduce the use of grapevine fungicides by nearly 90%.

Grapevine downy mildew attacks on vulnerable Vitis vinifera vine (A) and on a variety that is resistant to the disease (B).. © INRA, François Delmotte, Laurent Delière
Grapevine downy mildew attacks on vulnerable Vitis vinifera vine (A) and on a variety that is resistant to the disease (B). © INRA, François Delmotte, Laurent Delière

In 2017, INRA will add to its catalogue a series of grape varieties with partial resistance to the mildew. The effectiveness of these resistant varieties could be compromised, however, by the appearance of “virulent strains” after only a few years.

Grapevine downy mildew adapts to resistant grape varieties – Regent, Prior and Bronner – which reduces the effectiveness of the resistance (erosion). Effectiveness as a percentage is calculated in relation to a vulnerable variety (Cabernet Sauvignon) based on sporulation of the mildew, a major factor in how the disease spreads.. © INRA
Grapevine downy mildew adapts to resistant grape varieties – Regent, Prior and Bronner – which reduces the effectiveness of the resistance (erosion). Effectiveness as a percentage is calculated in relation to a vulnerable variety (Cabernet Sauvignon) based on sporulation of the mildew, a major factor in how the disease spreads. © INRA
As such, researchers in the Joint Research Unit for vine health and agroecology (SAVE) in Bordeaux (INRA-Sciences Agro) are developing ways to sustainably manage grape variety resistance. One issue is whether grapevine mildew will be able to adapt to the selective pressure exerted by resistant varieties. To find out, the aggressiveness of mildew strains collected from resistant vines was compared with that of “naive” strains which had never encountered resistance. The mildew populations studied came from Switzerland and Germany, where several resistant varieties of grapevine have already been planted. During one lab-based experiment, mildew strains on three German vine varieties (Regent, Prior, Bronner) were inoculated.

Results show that partial resistance in the vines is globally effective at combating the mildew: spore production fell by 58-92% compared to that found in vulnerable varieties (e.g. Cabernet Sauvignon).  However, scientists also observed that sporulation in resistant variety strains is greater and occurs earlier than in ‘naive’ strains (from vulnerable grape vine varieties).  On Regent and Prior, for example, adaptation in mildew populations leads to a reduction in resistance effectiveness of almost 26%.  On the resistant Bronner variety, effectiveness diminishes by 7%. This is known as partial resistance erosion.  In the case of Regent, this adaptation is very quick as well (less than five years), as observed by the same team of scientists in a previous study.

The team also showed that such changes in mildew populations does not appear to effect currently grown grape vine varieties. On Cabernet Sauvignon, for example (a vulnerable variety), ‘virulent’ mildew strains do not appear to be more aggressive than ‘naive’ strains.  Further experiments are needed to confirm this result.

Given that INRA will soon release new resistant varieties on the market, these results highlight the importance of taking into account the durability of a resistance.  INRA continues its focus on the creation of varieties with polygenic resistance, which include several types of  resistance to a single pathogen. This strategy of ‘pyramiding’ new varieties ensures a greater durability of resistance, even if it extends selection schemas.  Agronomists are studying how best to use these varieties and which growing options to choose to preserve the durability of these new viticultural systems.

Contact(s)
Scientific contact(s):

  • Chloé Delmas (33 (0)5 57 12 26 13) Joint Research Unit for Vine Health and Agroecology (INRA, Bordeaux Sciences Agro)
  • François Delmotte (33 (0)5 57 12 26 14) Joint Research Unit for Vine Health and Agroecology (INRA, Bordeaux Sciences Agro)
Press Relations:
INRA News Office (33 (0)1 42 75 91 86)
Associated Division(s):
Plant Health and Environment
Associated Centre(s):
Nouvelle-Aquitaine-Bordeaux

Reference

Chloé E.L. Delmas, Frédéric Fabre, Jérôme Jolivet, Isabelle D. Mazet, Sylvie Richart Cervera, Laurent Delière, François Delmotte. Adaptation of a plant pathogen to partial host resistance: selection for greater aggressiveness in grapevine downy mildew. Evolutionary Applications DOI:10.1111/eva.12368, 13 May 20016