Pinus pinaster

Photo JM Gion, CIRAD

Maritime pine is a major component of the French forest, where it covers 1.5 million hectares, or 10% of the national forest surface. With an average productivity of 9 m³/ha/yr, it represents 30% of the national production of coniferous wood. Outside of the Aquitaine massif (about 1 million ha), it is found in the west (Poitou-Charentes, Vendée, Sarthe, Basse-Normandie), in the Central region (forêt d’Orléans, Sologne), as well as in the Mediterranean zone (Cévennes, Corbières, Var, Alpes maritimes, Corsica). In Aquitaine, it is not only of ecologic value (this French region has the highest level of forestation), but it is also of indisputable economic importance, accounting for 30,000 jobs and a turnover equal to that of Bordeaux wines. The maritime pine forest also plays a key role in regional development of rural areas. The articulation between the resource and industry occurs as a coupling. This is expressed at the research level by strong wood science and genetic research, two disciplines which are being developed at the Forêt-Bois de Bordeaux-Pierroton research site.

The research activities which will use the genomic resources produced in the framework of the ForEST project and which already exist, aim to identify the genes implicated in the genetic control of wood quality and in the adaptation of maritime pine to water deficit.

Wood quality

The wood available as a raw material to Aquitaine manufacturers in the forest-wood-paper sectors does not always have the desired chemical and technological characteristics. Thus, although the stated objective of the research is to increase the yield of the wood, breeding efforts are oriented towards quality today. Measurements of wood properties are excessively costly and laborious, and it is hard to envisage using them in breeding in view of the constraints imposed by a tree improvement programme (thousands of measurements would be required). Thus marker-assisted selection (MAS) becomes of great importance. Since forest species are allogamous and not highly domesticated, the application of MAS at the population level should resolve the problem of the absence of physical linkage disequilibrium between alleles of markers and QTL alleles. The discovery of genes directly involved in the expression of traits of interest is therefore an essential step. It is a matter of choosing (molecular sorting, which is cheap and can be done early) among the collections of elite genotypes which have already been selected for vigor, those which possess forms which are favorable at the level of the genes controlling traits of interest, in order to create varieties with high technological performance rapidly. The target characteristics for breeding are:

• lignin and cellulose content and fiber morphology, which condition the efficacy and profitability of paper processes,
• the technological properties of the fibers and aggregates for composites (especially panels) and
• modulus of elasticity for utilization in carpentry.

This research programme responds not only to a need for purely scientific knowledge about molecular mechanisms involved in wood formation, but also targets a regional economic need.

Water and wood

The water supply constitutes the principal limiting factor for growth and survival of plants. For example, a maritime pine consumes around 800 to 900 liters of water in order to produce one kg of wood. This amounts to 400 m³ of water for 1 m³ of wood. However, we now know that in the next 50 to 100 years, global climate change will lead to a significant decrease in precipitation and an increase in summer temperature in the southern half of France. It is therefore likely that in the near future plants will have less water available than at the beginning of the century. Fifty years is just the time scale which corresponds to the duration of the life of a maritime pine forest, from when it is planted until cutting of the timber. It is therefore important to know if these organisms can support sudden climate changes; in other words, can the improved varieties that are planted today maintain the current productivity levels in an environment with less water, and can they tolerate episodes of intense drought? In fitting models of future climatic evolution with our knowledge on forest functioning, the ecophysiologists are already predicting a drop in productivity for maritime pine forests beginning in 2040 (especially in the Aquitaine massif). Scientists who are studying genetic factors that account for tree water use efficiency have furthermore shown that for the same quantity of water consumed, all trees do not produce the same quantity of wood. It therefore seems possible to utilize this variability to adapt our forests to a dryer climate, in particular by creating improved varieties which can maintain a reasonable growth rate and economize water at the same time, thus guaranteeing the sustainability and future competitiveness of the forest-wood-paper sector.

With the support of the Genoscope (ForEST project), the molecular biologists of INRA have recently begun the decoding of a part of the genome of the maritime pine, specifically targeting the genes which control the response of trees to drought. This involves both an understanding of the intimate mechanisms (at the physio-molecular level) used by Maritime pine to resist a more or less pronounced water deficit, and a study of the natural diversity which exists at the DNA level to help geneticists select the trees which are best adapted to the goal of production under dry conditions.