Digestibility and Cell-Wall Components of Alfalfa Following Selection for Divergent Herbage Lignin Concentration
- Kevin D. Kephart ,
- D. R. Buxton and
- R. R. Hill
Breeding schemes to improve alfalfa (Medicago sativa L.) forage quality based on total herbage chemical composition can result in altered morphology. Additionally, cell-wall composition of plant parts also may be altered. This study investigated the effects of divergent selection for lignin concentration in total herbage of alfalfa on concentration of cell-wall components and digestibility of stems. Two groups of alfalfa previously derived from herbage-based selection were studied. Group 1 consisted of six two-parent Syn-2 lines randomly selected from ‘Saranac-AR’ for high (HL) or low (LL) acid-detergent lignin (ADL) concentration in the total herbage. Group 2 had 11 HL and 13 LL lines produced from crossing pairs of parents of the Group 1 lines. Neutral-detergent fiber (NDF) concentration in stem bases was 4 and 3% greater in HL lines than in LL lines in Group 1 and 2, respectively. Likewise, herbage NDF concentration was 8% greater in HL than in LL lines of Group 1 and 4% greater in Group 2. There were no differences between divergent lines in NDF concentration of stem tops. Lignin concentration in cell walls of Group 1 was 8 and 6% greater in LL lines than in HL lines in stem tops and stem bases, respectively. In Group 2, the LL lines had 2% greater cell-wall lignin concentration than HL lines in both stem fractions. Total-herbage NDF concentration correlated more closely with leaf-to-stem ratio of entire plants (r = − 0.96 and −0.78 for Group 1 and 2, respectively) than with stem length and maturity. Thus, herbage-based selection for improved nutritive quality of alfalfa results in complex changes in stem cellwall component concentrations in addition to large morphological changes.
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