Genetic Study on Several Mechanical Properties of the Wood of Coffea arabica and Coffea canephora Coffee Trees

International audienceThe physical characteristics of wood are not usually taken into account when breeding perennial species grown for their fruits or seeds. In the coffee tree, stem breakage during harvesting and lodging during the growth period are major defects in some cultivars. Such defects are linked to certain wood physical and mechanical properties, such as density or rigidity, which can be characterized by a parameter used in the resistance of materials: the modulus of elasticity. Wood density and the longitudinal modulus of elasticity of stem segments of Coffea arabica L and C. canephora coffee trees were studied. C. arabica coffee trees derived from a diallel mating design, and C. canephora derived from a clone comparative trial. The modulus of elasticity was measured using an acoustic system based on an analysis of the vibrations produced by a blow to the end of a piece of wood of known geometry. The modulus of elasticity and the wood density of the coffee tree stems were highly heritable in both species and the wood from C. arabica was stiffer on average than that from C. canephora. C. canephora clone classification according to wood stiffness revealed the clones most liable to lodging. In this species, wood stiffness displayed strong broad sense heritability (0.64), indicating that this trait can be efficiently improved. This parameter could also be used as a predictor of other traits of agronomic interest, such as resistance to borer insects. The classification of C. arabica parents according to the wood characteristics of their progenies depended on their rate of introgression by the species C. canephora. These traits could therefore be used as a measure of introgression in this species. Use of coffee tree wood could also be considered, notably to derive value from the wood arising from the different pruning and cutting back operations