Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/28/2008
Publication Date: 9/22/2008
Citation: Casler, M.D. 2008. Agricultural Fitness of Smooth Bromegrass Populations Selected for Divergent Particle-Size Reduction Index. Crop Science. 48:1793-1798. Interpretive Summary: Increasing voluntary intake potential, the amount of a forage than a ruminant can consume in a meal, is a powerful way to improve livestock performance via increased forage quality. Intake is greatest in forages that breakdown rapidly during chewing, rumination, and digestion. We have developed a new laboratory tool that measures the resistance of grass leaves to breakdown. This procedure, particle-size reduction index (PSRI) can be used in a forage breeding program to develop forages that have more rapid and more thorough breakdown into smaller particles that are more easily digested and utilized by livestock. In this research, we have discovered that there may be some negative agronomic consequences to increased PSRI, including most notably a decrease in forage yield. However, none of the relationships were very strong, suggesting that we can increase PSRI without any negative consequences if we also select for forage yield and other agronomic traits at the same time. This informaiton will be important to other forage breeders and will eventually impact forage and livestock producers with the development of varieties with improved intake potential.
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 neutral detergent fiber (NDF) concentration are associated with reduced plant fitness, prompting the development of alternative approaches, such as particle-size reduction index (PSRI). The objective of this research was to characterize correlated selection responses of four fitness traits following divergent selection for PSRI. Twelve smooth bromegrass populations (four base populations and their Cycle-1 high-PSRI and Cycle-1 low-PSRI progeny) were evaluated for forage yield, ground cover, seed yield, and lodging. Divergent selection for PSRI resulted in a negative change in forage yield, ranging from -0.097 to -0.379 Mg ha-1 cycle-1 across the four base populations. Pleiotropy or very tight linkage between loci controlling forage yield and PSRI accounted for only about half of the variation due to selection. The greater inconsistency of forage yield selection responses across the four populations, the lesser proportion of forage yield sum of squares attributable to divergence (pleiotropy or tight linkage), and the reduced magnitude of linear selection responses for PSRI compared to NDF suggest that PSRI may be a more effective selection criterion for improving intake potential of smooth bromegrass.