Efficiency of Early Selection in Improving Biomass and Predicted Ethanol Yield in Switchgrass

Switchgrass (Panicum virgatum L.) takes 3 yr to reach maximum biomass yields, delaying selection and cultivar improvement. This study evaluated the efficiency of early selection in improving third-year biomass and ethanol yields in lowland switchgrass. Fifty-six full-sib families were planted in Knoxville and Crossville, TN, with 1-m spacing in a randomized complete block design. In 2012 to 2014, plants were evaluated for biomass yield, ethanol yield, and morphological traits at 8 wk after emergence and in years one through three. Trait means, efficiency of indirect selection, and genetic gain were calculated. Biomass yield differed significantly by year (92 g in yr 1, 1069 g in yr 2, and 1425 g in yr 3) while ethanol yield did not ((x) over bar = 63 mg g(-1)). Juvenile selection was ineffective. Biomass selection was most efficient using first-year fall height with genetic gains per year 2.4 times those of direct selection on third-year biomass. First-year biomass and second-year biomass, fall height, spring height, and tiller diameter also exhibited high efficiency (1.3 to 1.9). For ethanol yield, negative efficiency indicated selection for low first-year height and low second-year spring height, and tiller diameter would result in 1 to 1.3 times the genetic gain expected from direct selection on third-year ethanol yield. Results indicate that early selection and indirect selection using morphological traits may speed yield improvement due to greater selection efficiency and higher genetic gains.