Switchgrass (Panicum virgatum L.) Distribution, Genetic Diversity, and Pollen-Mediated Gene Flow

Switchgrass (Panicum virgatum L.) is a North American grass being optimized to serve as a biofuel crop. The cultivation of switchgrass carrying novel genes and traits has made ecological risk assessment (ERA) research critical for predicting the effects of pollen dispersal and pollen-mediated gene flow on local switchgrass populations and plant communities. The goals of this research were to: 1) Understand Panicum species distribution, habitat types, and plant communities; 2) Create a Lagrangian model of pollen dispersal informed by data on pollen longevity, size, and wind fields; 3) Determine the potential for interspecific hybridization between switchgrass and other Panicum species; 4) Characterize the genotypes in switchgrass populations in coastal grasslands and inland road verges. All studies were conducted in the northeastern U.S. (Ecoregion Level III: Northeastern Coastal Zone, Northeastern Highlands). In the first study, a botanical survey showed that switchgrass populations were common in three coastal habitat types (semi-natural, human impacted, and roadside) as well as two inland habitats (roadside and wastelands) outside of their expected range. In the second study, pollen longevity, pollen size, and wind fields were used to parameterize a Lagrangian mathematical model to predict pollen dispersal. Switchgrass pollen grains entrained in light, buoyant winds were predicted to travel up to approximately 3.5 km. A model incorporating stronger, directional winds predicted pollen dispersal up to about 6.5 km. In the third project, switchgrass flowers were crossed with flowers from four other Panicum species but did not produce hybrid progeny. However, technical challenges prevented robust analysis of interspecific sexual compatibility. In the last study, switchgrass plants collected from inland roadsides and coastal habits were analyzed using their DNA and simple-sequence repeat (SSR) molecular markers. The switchgrass plants in the study were genetically diverse; the majority of inland individuals were identified as Upland octoploids genotypes, while the majority of coastal individuals were identified as Lowland tetraploid genotypes. Collectively, these projects suggest that pollen-mediated gene flow from switchgrass biofuels plantations could potentially alter the genetics of local coastal populations, as well as the composition of natural or roadside plant communities