Efficiency of Spaced‐Plant Selection in Improving Sward Biomass and Ethanol Yield in Switchgrass

Abstract

Switchgrass (Panicum virgatum L.) is an important emerging biofuel crop. In breeding nurseries, plants are typically widely spaced; however, production is in densely planted swards. This disconnect may hinder cultivar improvement. This study measured the efficiency of low‐density, spaced‐plant selection on improving biomass and ethanol yield in a high‐density, simulated sward. Fifty‐six full‐sib families were clonally replicated in two adjacent nurseries in Knoxville, TN. The spaced‐plant nursery consisted of single plants on 1‐m centers. The simulated‐sward nursery was created by planting four by seven plants on 0.33‐m centers with 1‐m alleys. In 2013 and 2014, biomass yield, ethanol yield, and morphological traits were evaluated. Trait means, correlations, and efficiency of indirect selection (E) were calculated. Significant interaction (p < 0.05) between year and nursery was observed for all traits except ethanol yield. The identified high‐yielding ideotype differed between biomass and ethanol yield and between spaced‐plant and simulated‐sward nurseries. Selection under spaced‐plant conditions for simulated‐sward performance was efficient for ethanol yield (E = 0.96) but highly inefficient for biomass yield (E = −0.31). Several morphological traits evaluated under spaced‐plant conditions were identified as efficient indirect selectors for simulated‐sward biomass or ethanol yield. Results suggest selections for sward biomass yield may be more appropriate under sward‐like conditions, but that spaced‐plant nurseries are efficient for selection of ethanol yield performance under sward‐like conditions and for indirect selection of sward yield traits using morphological traits.