Responses to Divergent Phenotypic Selection for Fiber Traits in Timothy

Abstract

Selection based on fiber traits may make it possible to improve forage digestibility while maintaining plant biomass. Our objectives were to evaluate the effects of divergent phenotypic selection for fiber traits on timothy (Phleum pratense L.) digestibility, plant biomass, fiber component concentrations and their ratios, and to identify selection criteria that have effective and stable effects on timothy digestibility without affecting plant biomass. Fourteen populations derived by intercrossing plants selected for high or low values of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and cellulose (CEL) concentrations, and for ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) ratios were evaluated in a field experiment. Direct responses for the selected traits were significant for the NDF, CEL, ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) populations. Indirect responses for in vitro true digestibility (IVTD) and in vitro NDF digestibility (IVNDFD) were greatest for the ratios involving ADL. The ADL/CEL selection resulted in the most stable responses across years for IVTD and IVNDFD. Averaged over 2 yr, the IVTD and IVNDFD of the low ADL/CEL population were 27 g kg–1 DM and 33 g kg–1 NDF greater than those of the high ADL/CEL population. Furthermore, the low ADL/CEL population maintained its HEM and CEL concentrations and its plant biomass. Phenotypic selection based on ADL/CEL could be used to improve timothy DM digestibility without reducing plant biomass.