Categories of Resistance to Greenbug and Yellow Sugarcane Aphid (Hemiptera: Aphididae) in Three Tetraploid Switchgrass Populations

Switchgrass, Panicum virgatum L., has been targeted as a bioenergy feedstock. However, little is currently known of the mechanisms of insect resistance in this species. Here, two no-choice studies were performed to determine the categories (antibiosis and tolerance) and relative levels of resistance of three switchgrass populations (Kanlow–lowland ecotype, Summer–upland ecotype, and third generation derivatives between Kanlow × Summer plants, K×S) previously identified with differential levels of resistance to the greenbug, Schizaphis graminum (Rondani), and yellow sugarcane aphid, Sipha flava (Forbes). No-choice studies indicated that Kanlow possessed multi-species resistance, with high levels of antibiosis to both aphid species, based on aphid survival at 7 and 14 days after aphid introduction and cumulative aphid days, while K×S possessed low-to-moderate levels of antibiosis to S. flava . Further, functional plant loss indices based on plant height and biomass indicated that tolerance is an important category of resistance for Summer plants to S. graminum . These studies also indicated that Summer lacks both tolerance and antibiosis to S. flava , relative to the other switchgrasses tested, whereas K×S lack tolerance and antibiosis to S. graminum . These studies are the first attempt to analyze the categories of resistance in switchgrass and provide critical information for characterizing the biological mechanisms of resistance and improving our knowledge of the plant–insect interactions within this system.