Positive genetic correlation between forage yield and fiber of smooth Bromegrass

Voluntary intake potential of a forage crop is generally considered to be the most important feed characteristic regulating animal performance. Efforts to develop forage crops with reduced bulk volume, measured by neutral detergent fiber (NDF) concentration, have been associated with reduced plant fitness. The objective of this study was to evaluate a second cycle of divergent selection for NDF in four smooth bromegrass (Bromus inermis Leyss.) pedigrees and to determine if concomitant selection for spaced-plant vigor could counteract the loss in forage yield associated with selection for low NDF. In both high and low directions of Cycle-2, populations were created with and without concomitant selection for plant vigor. Selection responses for NDF and forage yield were linear through both cycles of selection in both directions. Although responses were not uniform across the four pedigrees, changes in NDF were reflected in changes in forage yield on all levels evaluated: selection direction (high vs. low NDF), individual cycles, and vigor selections. Although combined selection for low NDF and high vigor improved forage yield in the low-NDF direction for one of four pedigrees, it did not alter the strong positive relationship between NDF and forage yield across all populations and cycles. The genetic correlation between NDF and forage yield appears to be physiological in origin, caused largely by overlapping genic specificities (i.e., pleiotropy).

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