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CROP BREEDING & GENETICS

Agricultural Fitness of Smooth Bromegrass Populations Selected for Divergent Particle-Size Reduction Index

USDA-ARS, U.S. Dairy Forage Research Center, Madison, WI 53706-1108. Research supported by the College of Agricultural and Life Sciences, Univ. of Wisconsin, Madison, WI 53706-1197

^* Corresponding author (michael.casler{at}ars.usda.gov).

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 to improve intake, 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 (Bromus inermis Leyss.) 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.

Abbreviations: NDF, neutral detergent fiber • PSRI, particle-size reduction index