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CROP BREEDING & GENETICS

Response from Selection for Pectin Concentration and Indirect Response in Digestibility of Alfalfa

^a Dep. of Plant Breeding and Genetics, Cornell Univ., Ithaca, NY 14853
^b Dep. of Animal Science, Cornell Univ., Ithaca, NY 14853

^* Corresponding author (drv3{at}cornell.edu)

Genetic improvement of alfalfa (Medicago sativa L.) for increased pectin concentration, estimated by neutral detergent soluble fiber (NDSF), would improve the efficiency of utilization of its high protein and digestibility by ruminants. The objectives of this study were to: (i) estimate the realized direct response from one cycle of phenotypic selection for NDSF concentration; (ii) evaluate association of NDSF concentration with other forage quality traits, and; (iii) determine the impact of selection for NDSF concentration on in vitro dry matter digestibility (IVDMD) of alfalfa. Selection for NDSF was applied to five alfalfa populations from 1996 to 2000 and synthetic generation two seed was produced. Progress from selection for NDSF concentration was evaluated in plot trials for 2 or 3 yr at two locations near Ithaca, NY. Populations divergently selected for NDSF were 1.62 to 5.15 g kg^–1 of dry matter (DM) higher and 2.26 to 4.20 g kg^–1 DM lower, respectively, than their respective base populations. Neutral detergent soluble fiber concentration was negatively correlated with total cell wall concentration (CW), and proportions of neutral detergent fiber (NDF), cellulose, and lignin in the CW. A positive correlation existed between NDSF concentration and crude protein (CP) concentration and IVDMD. Populations bred for higher or lower NDSF concentration had 0.20 to 8.82 g kg^–1 DM higher IVDMD and 0.63 to 15.06 g kg^–1 DM lower IVDMD than their respective base populations. Selection for NDSF concentration and indirectly for CP, total CW concentration and composition, and IVDMD of alfalfa forage was successful.

Abbreviations: ADF, acid detergent fiber • ADL, acid detergent lignin • CEL, cellulose • CELCW, proportion of cellulose in the cell wall • CP, crude protein • CW, total cell wall • DM, dry matter • EIR, ethanol insoluble residue • EIRCP, ethanol insoluble residue crude protein • EIROM, ethanol insoluble residue organic matter • IVDMD, in vitro dry matter digestibility • HC, hemicellulose • HCCW, proportion of hemicellulose in the cell wall • NIRS, near infrared reflectance spectroscopy • NDF, neutral detergent fiber • NDFCP, neutral detergent fiber crude protein • NDSF, neutral detergent-soluble fiber • NDSFCW, proportion of NDSF in the cell wall