Lessons Learned In Six Generations of Divergent Breeding for IVDMD In Switchgrass.

Six generations or cycles of divergent breeding for decreased or increased in vitro dry matter digestibility (IVDMD) has been conducted in the ‘Trailblazer' base population.  In the breeding population, selection was initially only for low (C-1) or high IVDMD (cycles 1, 2, and 3).  In cycles 4 and 5, winter survival was included as selection criteria along with IVDMD. The first cycle of selection for high IVDMD resulted in the development and release of the cultivar ‘Trailblazer'.  Its improved IVDMD resulted in improved animal gains and beef production per hectare.  After 3 cycles of selection only for high IVDMD, winter survival was adversely affected.  In populations where high yield was included as selection criteria along with high IVDMD, the adverse effect on winter survival has not developed.  Divergent breeding for IVDMD resulted in significant changes in biomass yield, lignin concentration, lignin composition, and plant anatomy in addition to changes in IVDMD .  Switchgrass plants with improved IVDMD also had improved potential ethanol yields when evaluated in a saccrification and fermentation conversion process.  The use of IVDMD as a selection criterion in recurrent generations of breeding resulted in multiple changes in switchgrass plants.