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Pinot Noir can survive for 150 days without water supply, whereas disease-tolerant cultivars like Floreal, Vidoc and Voltis can only survive for 50 days. This was discovered by Sylvain Delzon, a specialist in ecophysiology at the French National Research Institute for Agriculture, Food and the Environment (Inrae). He tested 30 grape varieties for their drought resistance and came to the conclusion that Pinot Noir - together with Merlot, Cabernet Sauvignon and Silvaner - is the most robust. According to the research results, when there is a lack of water, air bubbles form in the juice-bearing vessels ("cavitation"), which leads to embolism and dehydration of the organs. The vines protect themselves against this by closing the stomata in their leaves to stop evaporation. If the drought continues, they shed their leaves to protect the trunk and their perennial components.
According to Delzon, vines are as sensitive to drought as tomatoes. He studied the risk of hydraulic failure during droughts in 329 vineyards around the world. "The vineyards of Cognac, with its 85 per cent Ugni Blanc, or Marlborough, with its 78 per cent Sauvignon, have everything to fear from climate change," he warns.
While Delzon has not seen purely drought-related vine death in Saint-Emilion or Napa over the past 20 years, he and his colleagues have found up to 12 per cent cavitation in the trunks, affecting growth and yield. He calls on grape breeders to include hydraulic resistance traits in genetic improvement programmes, in addition to downy mildew, powdery mildew or black spot disease: "You can definitely cross grape varieties to make them more drought tolerant.".
(al / source: vitisphere; photo: Inrae)