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

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 lowdensity, 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.