Selection for in Vitro Dry Matter Disappearance in Switchgrass Regrowth1

Abstract

The potential for genetic progress from selection for in vitro dry matter disappearance (IVDMD) of switchgrass (Panicum virgahm L.) regrowth forage has not been determined by breeders. Improved regrowth quality is needed to increase average daily gain of ruminants in mid‐ to late‐summer. In this study, 33 half‐sib families of switchgrass were evaluated over 2 yr for initial growth dry weight, IVDMD, and N concentration, and for regrowth IVDMD. The regrowth IVDMD was measured from plant samples taken in July (IVDMDl) and August (IVDMD2). Genetic variance estimates were obtained to predict direct selection responses and correlated responses using the modified ear‐to‐row procedure. Selection indices were also constructed to predict responses to multiple‐trait selection. Expected gains from direct selection for dry weight (1.19 kg plant−1), IVDMDl (666 g kg−1), and IVDMD2 (498 g kg−1) were 0.24 kg plant−1, and 50 and 35 g kg−1, respectively, while maximum gains from correlated responses were 0.02 kg plant−1, and 40 and 36 g kg−1, for the respective traits. An estimated index consisting of initial growth dry weight, IVDMD, N, and regrowth IVDMD2 provided simultaneous expected gains of 0.04 kg plant−1 for dry weight and 42 g kg−1 for IVDMD2. Switchgrass regrowth IVDMD may be improved without greatly altering dry matter yield per plant and should receive greater priority in cultivar development.