Forage Quality Variation in the U.S. Alfalfa Core Collection

Abstract

Alfalfa (Medicago sp.) is the most important perennial forage crop in the USA. The cultivars currently grown commercially are based on a limited and intermixed set of germplasm. Our objective was to survey the genetic variation in leaf and stem quality in the crop by analyzing the core collection of the U.S. alfalfa plant introductions. The 200 plant introductions of the core were planted at Rosemount, MN, in 1991 and 190 entries were sampled at flowering in 1992. Sixtyone entries were re‐sampled in 1993. Leaf and stem tissues were analyzed separately for crude protein, neutral and acid detergent fiber (NDF and ADF, respectively), acid detergent lignin, in vitro dry matter disappearance (IVDMD), and ficin degradable CP (FDCP). Additionally, stems were analyzed for cellulose concentration and enzymatic degradability, 24‐ and 96‐h in vitro NDF digestibility (IVNDFD),and lignin composition. For all forage quality traits, significant variation was found among the plant introductions. Concentration of NDF varied widely for leaves among entries, but relatively little variation occurred in stem NDF. The opposite trend occurred for IVDMD which varied more in stem material than leaves. This result was attributed to the high degree of variation in stem IVNDFD among the plant introductions. Stem FDCP was among the more variable traits measured. Quality traits of four contemporary check cultivars included in the trial were never as high or low as the extremes observed among the plant introductions. Significant sampling year effects were observed for most quality traits, but year × entry interactions were minimal. Concentration of NDF and IVDMD had significant negative correlations between leaf and stem values. In general, if leaf or stem quality was high, then the quality of the other plant part was low although this correlation was not large. Significant variation in forage quality traits exists in the U.S. alfalfa germplasm collection that could be used to improve the quality of commercial cultivars.