Researchers looking for ways make grape cultivation more resilient to climate change have found that a wild variety growing in the Atlas Mountains of North Africa could hold the key.
Climate change is increasing the need for artificial irrigation in agriculture, but when water evaporates, salts remain in the upper layers of soil. These residues increase plants' stress which can cause yields to decrease and even death of plants.
Grapevines are the fruit plant with the highest yield worldwide, and while they are among the plants with moderate salt sensitivity, when the salt concentration exceeds a certain threshold, functioning of membranes and proteins is impeded and the plant stops transpiration. This includes evaporation via the leaves, and a few days after the stress period begins, the leaves die.
“That is how we may succeed in adapting the grapevine – the fruit plant with the highest yield per area worldwide – to the impacts of climate change.”
To protect viticulture from these impacts, researchers at the Karlsruhe Institute of Technology (KIT) have been seeking to identify genetic factors that make the grapevine more resilient. A wild grapevine called Tebaba, that grows in the Atlas Mountains, has a much higher salt tolerance than cultivated varieties, and continues to grow even after salts have enters its leaves.
“Actually, grapevine is adapted well to drought," says Professor Peter Nick from KIT’s Joseph Gottlieb Kölreuter Institut for Plant Sciences. "At first glance, irrigation-caused salt should not represent a big problem. However, drier and hotter summers increase the need for additional irrigation.”
To gain insight into the physiological and metabolic processes, including photosynthesis, researchers compared Tebaba with a rootstock widely used in the Mediterranean.
“We slowly increased the salt stress to simulate an irrigated vineyard,” Nick says. “We found that Tebaba does not sequester sodium in the root, but reorganises its metabolic response in the presence of sodium.
"We assume that its salt tolerance cannot be attributed to a single genetic factor, but results from favourable metabolic fluxes that are mutually supportive.”
The researchers found that the metabolic processes in Tebaba leaves are more stable than in other varieties, and no harmful substances form. As a result, the wild grapevine can use its resources for photosynthesis and naturally prevents the cell walls from collapsing.
In viticulture, it is common practice to graft grapevines, so the shoots of highly fruit-bearing species are placed onto rootstocks of the most robust species to make them more resilient to drought or pests, but the study shows that it would not be reasonable to use Tebaba as a rootstock, as salt tolerance is not caused by the root, but by the leaves.
“We therefore recommend introgression of Tebaba’s genetic salt tolerance factors into commercial varieties by natural crossing. This should be accompanied by molecular biology analyses,” says Nick. “That is how we may succeed in adapting the grapevine – the fruit plant with the highest yield per area worldwide – to the impacts of climate change.”