Impact of the drought: genetically improved maritime pines are as resistant as native ones.
In a context of climate change and increasing extreme weather events, the question of drought resistance in cultivated species arises. In Nouvelle-Aquitaine (France), scientists from the Institut National de la Recherche pour l'Agriculture, l'Alimentation et l'Environnement (INRAE) are studying the case of Pine maritime in collaboration with the Office National des Forêts (ONF). The water-transport capacity of the natural races and of the genetically improved maritime pine varieties resulting from a selection programme initiated in the 1960s has been compared. Their results, published in Tree Physiology, show that genetically improved varieties of maritime pine have a greater water transport capacity and are as drought-resistant as natural populations.
In the maritime pine, as in all plants, water is supplied through conduits called xylem (*to see (see note below). These conduits irrigate the entire tree and transport sap from the roots to the top of the canopy to regulate the temperature of the leaves. It has been observed, particularly in wheat, that the efficiency and resistance of these xylem conduits may have been affected by domestication or successive genetic selections: modern wheats are more vulnerable to drought than their common ancestor. Researchers at INRAE have sought to provide some answers in the case of a tree species that is the subject of an advanced genetic improvement programme: the maritime pine.
By studying 22 functional traits related to the hydraulic efficiency and safety of the xylem, the research team demonstrated that, compared with the ancestral maritime pine populations, the improved varieties created by INRAE and the technological institute FCBA (Forêt Cellulose Wood Construction Furniture) within the framework of the scientific interest group “Future Maritime Pine Group“** are more effective in transporting water.
On the left, the capacity of the xylem vessels to transport water. On the right Resistance of the vascular system to water stress. VNAT: natural population. VSEL, VF2, VF3: three successive generations of genetic improvement of maritime pine.
This greater efficiency in water transport is partly due to the larger diameters of the xylem vessels, whereas vulnerability to drought depends on the pore anatomy between the vessels, which has not changed across successive generations of improved varieties. Therefore, they are as drought-resistant as natural populations.
These results are important for the forestry and timber industry, as the new maritime pine plantations established each year in France (between 15,000 and 20,000 hectares) are planted almost exclusively with improved varieties. They also suggest that genetic resources more resistant to cavitation should be sought to tackle extreme droughts without reducing growth performance.
Xylem, water transport and drought resistance in plants
The xylem constitutes the conduits that transport water in plants and trees from the roots to the leaves. The capacity of these conduits to transport water depends mainly on their size, but also on their proper or improper functioning. During periods of drought, air bubbles can form in the vessels and cause gas embolisms, blocking the flow of water in the xylem. If too many embolisms occur in the conducting elements, water circulation ceases to be sufficient and the plant can die. A plant's drought resistance therefore corresponds to its ability to keep its xylem functional, that is, to prevent embolies from occurring.
He Scientific interest group:“Future Maritime Pine Group”It coordinates and carries out research and development activities in the fields of sustainable management of the cultivated maritime pine forest: risk management and adaptation, conservation of genetic resources and variety development, silviculture and modelling of production systems. This scientific interest group, established in 1995, brings together various actors in research, development and management in Nouvelle-Aquitaine: the National Institute for Agricultural Research, he Consumer Price Index (Centre for Productivity and Forestry Action of Aquitaine), he Federal Court of Appeal (Forestry, Pulp, Wood, Construction and Furniture Technology Institute), the What's Not Forgotten (National Forestry Office) and the Civilian Range Patrol Force (Aquitaine Regional Centre for Forestry Property).
