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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #188479


item Jung, Hans Joachim
item Lamb, Joann

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2006
Publication Date: 9/8/2006
Citation: Jung, H.G., Lamb, J.F. 2006. Stem morphological and cell wall traits associated with divergent in vitro fiber digestibility in alfalfa clones. Crop Science. 46:2054-2061.

Interpretive Summary: While alfalfa is the most important perennial forage crop fed to dairy cattle, its nutritional quality is limited by the low digestibility of alfalfa stem material. Alfalfa stems are high in fiber content and this fiber is generally poorly digested. Improving alfalfa stem fiber digestibility through traditional plant breeding and using molecular genetics is being pursued by public and private sector scientists. We conducted a study to determine which aspects of alfalfa stems were different among groups of plants that had been selected as genetically high or low for stem fiber digestibility. Compared to low digestibility plants, those alfalfa plants that had rapidly digested fiber had shorter stems and less fiber, but the chemical composition of the fiber was relatively unchanged. In contrast, alfalfa plants that had high amounts of digestible fiber had longer stems and reduced amounts of lignin, a fiber component that limits digestibility, but the same amount of fiber as low digestibility plants. Understanding what changes in alfalfa stem traits are associated with higher fiber digestibility will assist plant breeders and molecular biologists in targeting genetic improvement efforts at the most important critical traits to enhance this important crop.

Technical Abstract: Low fiber digestibility of alfalfa (Medicago sativa L) stems limits the energy available to ruminants from this crop. The objective of this study was to compare alfalfa clones identified with either low or high rapid (16 h), or low or high potential (96 h) stem in vitro neutral detergent fiber digestibility (IVNDFD) for stem fiber, cell wall, and morphology traits. The clones were established in replicated field plots at two locations in Minnesota during 2001 and harvested twice (primary spring growth and first summer regrowth) in the two following years. Presence of flowers, stem length, internode number, mean internode length, and number of elongating internodes were determined on 10 stems from each plot at every harvest. Remaining herbage was dried and the stem fraction was analyzed for 16- and 96-h IVNDFD, detergent fiber system components, and cell wall concentration and composition (Klason lignin, individual neutral sugars, and total uronic acids). Stem fiber and cell wall concentration were lower for the high rapid than low rapid IVNDFD clones, but the high and low potential IVNDFD clonal-groups did not differ from one another. Lignin and pectin concentrations of the cell wall were lower and higher, respectively, for both high IVNDFD groups than their corresponding low groups. The low rapid and high potential IVNDFD groups had longer stem and internode lengths than their corresponding groups. Most, but not all, of the differences between IVNDFD phenotype groups in cell wall traits agreed with previous predictions for traits related to fiber digestibility.