Heterosis and Reciprocal‐cross Effects in Tetraploid Switchgrass

ABSTRACT Switchgrass (Panicum virgatum L.) is a candidate for cellulosic bioenergy feedstock development in many parts of North America. Because production costs are generally considered too high for economic and sustainable production of switchgrass biomass, breeding for increased biomass yield is a viable and desirable research objective. The objective of this study was to estimate heterosis and reciprocal‐cross effects in three types of switchgrass crosses: upland × upland (U×U), lowland × lowland (L×L), and upland × lowland (L×U) hybrids. A total of 62 hybrids and two parental populations were evaluated for 2 yr at two Wisconsin locations. Mid‐parent heterosis for biomass yield was observed in only four L×L hybrids and no L×U hybrids, suggesting that it is not a universal phenomenon between upland and lowland ecotypes. Reciprocal effects were more important than heterosis effects, as most hybrids were similar in performance to their maternal parent population. Flowering time was a strong driver of biomass yield, accounting for 67% of the variation among hybrids in biomass yield and increasing biomass yield by 0.47 Mg ha−1 for each day delay in flowering time.