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Title:   Author  item
                                            Lamb, Joannitem
                                            JUNG, HANS-JOACHIM - University Of Minnesotaitem
                                            Samac, Deborah

                                                         - *Debby*
  Submitted to: Crop Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 5/7/2014
                                    Publication  Date: 5/27/2014
                                    Citation: Lamb, J.F., Jung, H.G., Samac, D.A. 2014. Environmental variability and/or stability of stem fiber content and digestibility in alfalfa. Crop Science. DOI: 10.2135.cropsci2014.04.0323.Interpretive Summary: Alfalfa is the most important perennial forage crop fed to dairy cattle, but its nutritional quality is limited by the low digestibility of alfalfa stems. Alfalfa stems are high in fiber content and this fiber is generally poorly digested. Alfalfa stem fiber content and digestibility are affected by growth environment (location, year and harvest date). Knowledge of the extent of these environmental influences on stem fiber content and digestibility is essential for traditional plant breeding programs with goals of improving stem fiber quality and digestibility in alfalfa. We conducted a study to compare alfalfa stem fiber content, stem lignin content, stem lignin as a proportion of stem fiber, stem rapid fiber digestibility, and stem total fiber digestibility across twelve harvest environments. Results showed that stem lignin as a proportion of stem fiber proved to be the most stable and consistent across the growth environments we evaluated.  Selection programs to decrease stem lignin should increase both rapid and total stem fiber digestibility without decreasing stem fiber concentration in alfalfa. These results increase our understanding as to which alfalfa stem traits are the most environmentally stable and how they are associated with higher fiber digestibility and will assist plant breeders and biologists in targeting genetic improvement efforts to enhance the nutritive value of this important crop.
                                Technical Abstract: The concentration and low digestibility of stem fiber constituents in alfalfa, Medicago sativa L, herbage can limit dry matter intake and energy availability in dairy and beef production systems. Stem neutral detergent fiber (NDF), acid detergent lignin (ADL), and stem neutral detergent fiber digestibility (NDFD) are affected by environmental influences. Knowledge of the extent of environmental influence and variability of these stem quality traits will be essential in a plant breeding program with goals to improve these traits. We initiated a study to identify individual alfalfa plants that differed (highest and lowest) in stem NDF and ADL concentrations, ADL as a proportion of NDF (ADL/NDF) and stem in vitro neutral detergent fiber disappearance (IVNDFD) after 16 and 96 hours of digestion. Forty-five individual plants (clones) were identified and established in replicated experiments at two field locations and sampled for spring, early and late summer harvests for two years (12 harvest environments). Stability analysis and ranked correlations demonstrated that stem ADL/NDF was the most stable and repeatable and 16-h IVNDFD the least stable in the field environments tested. No association between the performance of the clones in greenhouse and field environments was found for any of the five stem fiber quality traits. Selection for decreased stem ADL/NDF showed the greatest potential for field selected improvement of alfalfa stem fiber digestibility.


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