Variation in Biomass Yield, Cell Wall Components, and Agronomic Traits in a Broad Range of Diploid Alfalfa Accessions

Alfalfa (Medicago sativa L.), one of the most important forage legumes throughout the world, has potential as a biofuel crop. Breeding to improve biomass yield and stem composition will enhance the value of alfalfa. In this experiment, we evaluated 374 individual genotypes from 120 accessions of wild diploid alfalfa collected throughout the Northern Hemisphere and representing the three diploid subspecies, M. sativa subsp. falcata, M. sativa subsp. caerulea, and M. sativa subsp. hemicycla. We measured total biomass yield, stem cell wall constituents (neutral detergent fiber, acid detergent fiber, acid detergent lignin, glucose, xylose, and arabinose), and important agronomic traits in field trials at two Georgia locations in 2007 and 2008. A large amount of phenotypic variation exists in the diploid gene pool for all traits. Yield variation among accessions spanned more than an order of magnitude. High-yielding accessions tended to have higher levels of cell wall constituents. Clustering of genotypes or accessions on the basis of phenotypic traits differed from the population structure pattern observed previously with molecular markers. The results show that phenotypic variation is very large in diploids, offering a potentially useful pool of alleles for future breeding efforts.