Genetic improvement of alfalfa for ethanol production requires high throughput screening of cell wall (CW) degradability. We developed an efficient enzymatic test to assess the degradability of alfalfa stems. In spite of its robustness, this technique is labour intensive, thus limiting analytical capabilities. Near infrared reflectance spectroscopy (NIRS), which requires minimal sample preparation, has been used to accurately predict carbohydrate fractions in alfalfa. Here, we used NIRS to predict CW glucose released by enzymatic saccharification. Our objective was to identify genotypes with high and low degradability to assist alfalfa improvement for ethanol production.

Stems of individual alfalfa plants from each of winterhardy-type and biomass-type populations were ground and scanned using a NIRS system 6500 monochromator. Resulting spectra were related to the chemical analyses of carbohydrates and CW fractions (NREL LAPs), and sugars released by an enzymatic cocktail consisting of Accelerase 1500 + xylanase + cellulase (Genencor) + pectinase (Sigma).

NIRS prediction of glucose released by enzymatic saccharification provided a good estimate of cell wall degradability. Predictions over 621 genotypes revealed a large variability of CW degradability within and among the different alfalfa genetic backgrounds. Predictions also highlighted the negative relationship between lignin content and CW degradability.

Our results show that NIRS can be used to estimate CW degradability and to select genotypes with high and low degradability. These genotypes are currently used to develop SRAP markers and to produce new germplasms that combines superior CW degradability with enhanced biomass and winter survival traits.