Effect of Low Lignin Genes (COMT and CCOMT) On Alfalfa Forage Quality.

We determined the change in forage quality of two reduced lignin transgenic alfalfa (Medicago sativa L.) populations, compared to appropriate controls and grown in diverse environments.  Alfalfa populations for this study consisted of transgenic alfalfa lines down-regulated for one of two lignin biosynthetic genes (caffeic acid 3-O-methyltransferase (COMT) or caffeoyl CoA 3-O-methyltransferase (CCOMT)), their null isogenic lines, and a check variety (LegenDairy 5.0).  Replicated studies were conducted at Becker, MN; Arlington, WI; West Salem, WI; Davis, CA and Tulelake, CA.  The experimental design was a split plot with harvest dates as whole plots and entries as sub plots.  Plants were started in the greenhouse and then transplanted into the field in spring 2008 into rows spaced 30 cm apart with 30 cm between rows.  Each plot consisted of three rows of 9 plants. The middle 7 plants of the middle row were harvested for yield and quality in summer 2008.  Harvests were taken beginning at late vegetative stage and continued at 5 day intervals for 5 total harvests. Forage samples were analyzed for crude protein, Neutral detergent fiber (NDF), acid detergent lignin (ADL), and neutral detergent fiber digestibility (NDFD). The CCOMT line averaged 120g/kg less ADL than the null and had 102g/kg more NDFD.  The COMT line averaged 37g/kg less ADL than the null and had 140g/kg more NDFD.  A change in lignin composition in the COMT population is a likely explanation for the increased fiber digestibility relative to lignin content.  In this study late harvested COMT and CCOMT lines had the same NDFD as the nulls or commercial check harvested 8 to 12 days earlier.  Producers using this trait may be able to delay harvest while maintaining forage quality, potentially eliminating one or more annual harvests and while increasing yield by 20 to 30%.