Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2008
Publication Date: 11/24/2008
Citation: Casler, M.D., Diaby, M. 2008. Positive Genetic Correlation Between Forage Yield and Fiber of Smooth Bromegrass. Crop Science. 48:2153-2158. Interpretive Summary: Our research goal is to increase the ability of ruminant livestock to consume forage grasses by improving the intake potential of the forage. To do this, the scientific literature indicates that we should decrease fiber content of the forage. All of our attempts to do this have met with huge decreases in forage yield as a result of genetic selection for reduced fiber content. In this study, we attempted to counteract this problem, by simultaneous selection for reduced fiber and increased forage yield in smooth bromegrass. All such attempts failed, verifying that forage yield and fiber have a true positive genetic correlation that cannot be broken. Future efforts by forage breeders to improve intake potential of forages should focus on different traits, such as particle-size reduction or shear strength.
Technical Abstract: 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, are 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 pedigrees, 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, ie. pleiotropy.