FORAGE QUALITY VARIATION IN THE US ALFALFA CORE COLLECTION

Alfalfa (Medicago sp.) is the most important perennial forage crop in the USA. The cultivars currently grown commercially are based on a lim ited and intermixed set of germplasm. Our objective was to survey the genetic variation in leaf and stem quality in the crop by analyzing th e core collection of the U.S. alfalfa plant introductions. The 200 pla nt introductions of the core were planted at Rosemount, MN, in 1991 an d 190 entries were sampled at flowering in 1992. Sixty-one entries wer e re-sampled in 1993. Leaf and stem tissues were analyzed separately f or crude protein, neutral and acid detergent fiber (NDF and ADF, respe ctively), acid detergent lignin, in vitro dry matter disappearance (IV DMD), and ficin degradable CP (FDCP). Additionally, stems were analyze d 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 plan t introductions. Concentration of NDF varied widely for leaves among e ntries, but relatively little variation occurred in stem NDF. The oppo site 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 mor e variable traits measured. Quality traits of four contemporary check cultivars included in the trial were never as high or low as the extre mes observed among the plant introductions. Significant sampling gear effects were observed for most quality traits, but year x entry intera ctions were minimal. Concentration of NDF and IVDMD had significant ne gative 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.