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FORAGE & GRAZINGLANDS

A Comparative Study of Alfalfa and Medicago truncatula Stem Traits: Morphology, Chemical Composition, and Ruminal Digestibility

^a USDA-ARS Plant Science Res. Unit, Dep. of Plant Pathology, 495 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108
^b USDA-ARS Plant Science Res. Unit, Dep. Agronomy and Plant Genetics, 411 Borlaug Hall, 1991 Upper Buford Circle, Univ. of Minnesota, St. Paul, MN 55108. Current address for J.A. Schnurr: Cargill, Inc., 2540 E. Drake Rd., Fort Collins, CO 80525. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the USDA, and does not imply its approval or the exclusion of other products and vendors that might also be suitable

^* Corresponding author (Hans.Jung{at}ars.usda.gov).

Alfalfa (Medicago sativa L.) is an agronomically important forage, but digestibility of stem cell wall material is low. Because the tetraploid genome of alfalfa complicates genetic dissection of complex pathways, the diploid M. truncatula Gaertn. could serve as a model for stem cell wall development in alfalfa. We compared stem morphology, chemical composition (protein, soluble carbohydrates, cell wall polysaccharides, and lignin), and in vitro ruminal cell wall polysaccharide digestibility of two alfalfa clones (Regen-SY27 and 718) and four M. truncatula inbred lines (A17, A20, DZA315.16, and R108) in a replicated growth chamber experiment. Stem tissue development and cell wall lignification observed by light microscopy were similar between the species. While differences in stem morphology, composition, and digestibility were observed among the germplasms, there was overlap between the alfalfa and M. truncatula germplasms for all traits except protein concentration, which was greater for the two alfalfa clones. Younger stem internodes (top third of the stem) of both species had a higher protein concentration and greater cell wall polysaccharide digestibility, and lower cell wall concentration than older internodes (bottom third of stem). Based on the data presented here, it appears that M. truncatula is a suitable model for stem development, composition, and digestibility of alfalfa.

Abbreviations: ADL, acid detergent lignin