Characteristics of Timothy Genotypes Divergently Selected for Fiber Traits

Abstract

Selection for reduced fiber concentration in forage crops is considered to be an effective approach to improve digestibility but often results in reduced dry matter (DM) yield. The objective of this study was to characterize timothy (Phleum pratense L.) genotypes divergently selected for fiber component concentrations and their ratios, and to identify selection criteria that could have a meaningful effect on timothy digestibility without adversely affecting DM yield. Divergent phenotypic selection was applied for neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), hemicellulose (HEM), and cellulose (CEL) as determined by the detergent fiber system of forage analysis and for ratios of ADL/HEM, ADL/CEL, ADL/(HEM+CEL), and HEM/CEL among 78 high yielding plants selected from among 2000 spaced plants from four populations. For each criterion, the two plants with the highest and the two plants with the lowest values within each population were selected. These plants were vegetatively propagated and composition of spring growth was evaluated in a 2‐yr field experiment. The divergent NDF, ADF, ADL, CEL, ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) groups of genotypes were significantly different for their respective trait. The ADL, ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) groups were the most stable across years for in vitro true digestibility (IVTD), with the low groups having values of IVTD between 10 and 34 g kg−1 DM above those of the corresponding high groups. The DM yield of the low‐ADL/(HEM+CEL) and‐ADL/CEL groups were also greater than that of their corresponding high groups by more than 13%. Therefore, ADL/(HEM+CEL) and ADL/CEL seem to be promising selection criteria to increase digestibility while maintaining or increasing DM yield.