Genetic differences in chemical composition among alfalfa plant introductions, varieties, and individual genotypes have been reported. Leaf and stem CP differed among a group of 61 plant introductions, although the ranges were small, from 272 to 295 and 88 to 99 g CP kg-1 DM, respectively (Jung et al., 1997). Leaf NDF concentration (235 g kg-1 DM) did not differ significantly among these plant introductions, but stem NDF ranged from 636 to 670 g NDF kg-1 DM. Similar variation was observed among a group of five commercial alfalfa varieties with CP and NDF differences being noted for leaves and stems, as well as whole herbage (Sheaffer et al., 2000). Differences in stem cell wall concentration and composition were observed among a set of four alfalfa genotypes selected for divergence in whole herbage ADL and in vitro ruminal DM disappearance (IVDMD) (Jung et al., 1994) and a group of three genotypes selected for divergent IVDMD (Jung and Engels, 2002). More recently, alfalfa genotypes selected for divergent cell wall Klason lignin, cellulose, and xylan were shown to differ genetically for these cell wall components when grown across a series of envi­ronments (Lamb and Jung, 2004). While the reported genetic variation among alfalfa germplasm sources is not large, the potential for modifying cell wall composition has not been seriously explored, because recurrent selection for these traits has not been done.

Significant genotype x environment (G x E) interactions have generally not been observed for chemical composition of alfalfa varieties. Among 61 plant introductions, no measures of cell wall concentration or composition were found to have significant G x E interactions for leaf or stem material (Jung et al., 1997). Only differences in magnitude, not rank, for composition due to G x E interactions were noted by Sheaffer et al. (2000) among five alfalfa varieties. These results mirror the conclusion of Buxton and Casler (1993) that forage quality traits generally have small G x E interaction effects compared to the impact on yield. However, in recent work with alfalfa clones selected for specific cell wall traits, it was found that G x E interactions were significant among plants selected for low and high pectin and xylan concentrations, whereas no G x E interactions were noted among clones selected for Klason lignin or cellulose (Lamb and Jung, 2004).