Varietal selection of flax over time: Evolution of plant architecture related to influence on the mechanical properties of fibers

The varietal selection of flax (Linum Usitatissimum L.) has always focused on specific criteria fulfilling requirements of farmers and textile workers. Thus, the current development of composites using flax as reinforcement presents new challenges for flax breeders in terms of fiber quantities and quality. However, the impact of the varietal selection on the mechanical properties of resulting fibers is yet to be determined. In the present study, several architectural characteristics of flax stems are defined. Stem transverse sections from four varieties selected from the 1940s to 2011 are compared. Anatomical changes over time are highlighted. The most important ones involve the gap between fiber bundles and the amount of fibers which can be improved with the selection (from 7.8% to 13.4% of the tissue area per section). This trend coincides with the increase in biomass production over time expected from the selection work. Moreover, this study demonstrates that flax fibers preserve their good mechanical performances in spite of the anatomical differences. Thus, through varietal selection, it is possible to increase the biomass yield while preserving the excellent specific mechanical properties of flax fibers. Finally, flax fibers can compete with glass fibers to reinforce composite materials.