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Title: Categories of resistance to greenbug and yellow sugarcane aphid (homoptera: aphididae) in three tetraploid switchgrass populations

Author
item KOCH, KYLE - University Of Nebraska
item HENG-MOSS, TIFFANY - University Of Nebraska
item BRADSHAW, JEFF - University Of Nebraska
item Sarath, Gautam

Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2014
Publication Date: 8/25/2014
Publication URL: http://handle.nal.usda.gov/10113/59535
Citation: Koch, K.G., Heng-Moss, T.M., Bradshaw, J.D., Sarath, G. 2014. Categories of resistance to greenbug and yellow sugarcane aphid (homoptera: aphididae) in three tetraploid switchgrass populations. BioEnergy Research. 7: 909-918. DOI 10.1007/s12155-014-9420-1

Interpretive Summary: Large scale plantings of switchgrass for bioenergy could become susceptible to insect herbivory resulting in the loss of biomass yields. Among the range of insects that can feed on switchgrass, piercing-sucking insects such as aphids could cause extensive damage to standing crops. Aphids are among the most important insect pests of cultivated crops. It therefore becomes important to understand the extent of resistance in switchgrass populations to aphids that are known to be pests of related plant species such as sorghum and sugarcane. In this study, three populations of switchgrass were evaluated for their ability to serve as hosts for two insect pests, the greenbug and the yellow sugarcane aphid. Results indicated that switchgrass cultivar Summer could tolerate greenbug infestations, but were susceptible to the yellow sugarcane aphid. Whereas, switchgrass cultivar Kanlow, which has high biomass yields, was mostly resistant to both insects suggesting that Kanlow plants contained compounds that deterred insect feeding and/or negatively impacted their survival. A population derived from hybridizing Kanlow and Summer plants (K x S) which has high winter survival and high yields was tolerant to feeding by the yellow sugarcane aphid, but was susceptible to feeding by greenbugs. These studies will be foundational to understanding the cellular and molecular mechanisms underpinning these responses. Ultimately these studies will be used to improve switchgrass germplasm.

Technical Abstract: 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, Summer, and hybrids between select Kanlow x Summer plants, KxS) 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 KxS 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 KxS hybrids 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.