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Switchgrass (Panicum virgatum L.) is a main herbaceous species projected for use as feedstock in biofuel production. Understanding the nature of genetic variation for biomass yield and other important traits in switchgrass would aid cultivar development. The aim of this study was to estimate the genetic component of variation and narrow‐sense heritability for biomass yield and several morphological and phenological traits in lowland switchgrass. Thirty‐seven half‐sib families were evaluated during 2007–2009 at two south central Oklahoma locations, Ardmore and Burneyville. Half‐sib families were different for biomass yields and other traits, suggesting the presence of additive gene action in controlling these traits. Family × location effects were observed for biomass yield and days to spring regrowth. Stem thickness, plant spread, and spring regrowth showed family × year interaction effects. Days to flowering showed a significant family × location × year interaction. Narrow‐sense heritability for biomass yield was 0.13 based on half‐sib family variation and 0.29 based on parent–progeny regression, suggesting a complex genetics of biomass yield. Stem thickness also had low (≤0.27) and plant height and tillering ability had low to moderate (0.26–0.48) heritability. Heritabilities were moderate (0.47–0.70) for heading, flowering, and plant spread and relatively high (≥0.82) for spring regrowth. The biomass yield was positively correlated with tillering ability, plant height, and stem thickness. Rigorous family evaluation procedure and use of tillering ability as an indirect measure to improve biomass yield could enhanced gain from selection.

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