Assessment of Genetic Variability of Cell Wall Degradability for the Selection of Alfalfa with Improved Saccharification Efficiency

Alfalfa (Medicago sativa L.) has a high potential for sustainable bioethanol production, particularly because of its low reliance on N fertilizer. We assessed near-infrared reflectance spectroscopy (NIRS) as a high-throughput technique to measure cell wall (CW) degradability in a large number of lignified alfalfa stem samples. We also used a powerful immunological approach, glycome profiling, and chemical analyses to increase our knowledge of the composition of CW polysaccharides of alfalfa stems with various levels of degradability. NIRS accurately predicted CW degradability in four different alfalfa cultivars, as assessed by glucose released following enzymatic saccharification (R (2) = 0.94). There was a large genetic diversity for enzyme-released glucose. The 10 genotypes with the highest (D+) and 10 genotypes with the lowest (D-) amounts of enzyme-released glucose of a biomass-type (Orca) and a winterhardy-type (54V54) cultivar were further characterized. Glycome profiling showed that there were very few differences in CW polysaccharide composition between the two groups, although the D+ genotypes were at least 35 % more degradable than the D- genotypes. Determination of CW composition by chemical analyses showed that a higher lignin content of the D- genotypes was closely related to their lower enzyme-released glucose (R = -0.83). In each cultivar tested, 20 D+ genotypes and 20 D- genotypes were intercrossed to generate D+ and D- populations. Assessment of CW enzyme-released glucose in the progenies showed that this trait is genetically inherited. The large genetic diversity for enzyme-released glucose and its potential for selection support the huge potential of alfalfa for the sustainable production of bio-ethanol.