Biochemical, physiological, and anatomical insights into aphid-bioenergy switchgrass interactions

Switchgrass, Panicum virgatum L., a perennial, warm-season grass native to North America, is a candidate for development as a bioenergy crop. Previously, warm-season grasses were considered to be relatively pest free in their native habitats. However, recent studies using the hemipteran family Aphididae have shown phloem-feeding insects can lead to significant injury in switchgrass. The objectives of this research were to: 1) gain physiological, biochemical, and anatomical insights into insect-bioenergy switchgrass interactions to determine potential insect resistance mechanisms among susceptible and resistant switchgrass genotypes; and 2) to generate and evaluate diverse segregating populations of switchgrass, both resistant and susceptible, to assess for insect herbivory. Recently, select aphids including greenbugs, Schizaphis graminum (Rondani), and yellow sugarcane aphids, Sipha flava (Forbes), have been identified as potential pests of switchgrass. However, limited research has been devoted to selecting insect-resistant switchgrasses and understanding the physiological responses of susceptible and resistant switchgrasses to aphid feeding. Using a series of photosynthesis studies, differences in photosynthetic activity were detected among the switchgrasses evaluated in response to aphid feeding. Overall, the lowland ecotype (Kanlow) assimilated carbon dioxide more efficiently than the upland ecotype (Summer) and the hybrid KxS when exposed to aphid herbivory. These observations suggest the antibiotic population, Kanlow, has mechanisms similar to those observed in tolerant plant systems where changes in photosynthetic rates occurred in response to aphid herbivory. Feeding by greenbugs and yellow sugarcane aphids on plants can elicit a number of stress-related responses. Our studies investigated the accumulation of reactive oxygen species (ROS) scavenging enzymes and defensive response genes in resistant and susceptible switchgrass populations using biochemical protocols along with gene expression studies. Genes of interest involving greenbug-switchgrass interactions were identified from previous Illumina ® Solexa data, specifically RNAseq. These data provide valuable insight into the physiological, biochemical, and anatomical response of switchgrass when challenged by cereal aphids. Furthermore, continued screening of susceptible and resistant switchgrass germplasm will help researchers better understand the defensive systems operating in segregating switchgrass populations