Fall armyworm (spodoptera frugiperda smith) feeding elicits differential defense responses in upland and lowland switchgrass

Authors: Palmer, Nathan - Nate; BASU, SAUMIK - University Of Nebraska; HENG-MOSS, TIFFANY - University Of Nebraska; BRADSHAW, JEFFREY - University Of Nebraska; Sarath, Gautam; LOUIS, JOE - University Of Nebraska

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2019
Publication Date: 6/13/2019
Citation: Palmer, N.A., Basu, S., Heng-Moss, T., Bradshaw, J.D., Sarath, G., Louis, J. 2019. Fall armyworm (spodoptera frugiperda smith) feeding elicits differential defense responses in upland and lowland switchgrass. PLoS One. 14(6):e0218352. https://doi.org/10.1371/journal.pone.0218352.
DOI: https://doi.org/10.1371/journal.pone.0218352

Interpretive Summary: Chewing insects, such as the generalist feeder Fall armyworm (FAW) can cause significant economic damage to a number of cultivated grasses. Mitigating these losses through identification of resistant plant germplasm has been a focus for several crop and grass breeding programs. Here two switchgrass cultivars, namely Summer and Kanlow, with divergent responses to other insects were evaluated to their ability to withstand herbivory by FAW larvae. FAW larvae feeding on Kanlow seedlings for ten days weighed significantly less than those feeding on Summer seedling. Relative expression of genes in Summer and Kanlow plants following ten days of FAW herbivory were evaluated using high-throughput sequencing. These data indicated that although both Kanlow and Summer plants induced defense-related genes in response to FAW feeding, Kanlow plants mounted a more robust defensive response. Overall, these data affirm that the cultivar Kanlow can provide useful genetics for the breeding of switchgrass germplasm with improved insect resistance.

Technical Abstract: Switchgrass (Panicum virgatum L.) is a low input, high biomass perennial grass being developed for the bioenergy sector. Upland and lowland cultivars can differ in their responses to insect herbivory. Fall armyworm [FAW; Spodoptera frugiperda JE Smith (Lepidoptera: Noctuidae)] is a generalist pest of many plants and can feed on switchgrass as well. Here, in two different trials, FAW larval weights were significantly reduced when fed on lowland cultivar Kanlow relative to larvae fed on Summer plants after 10 days. Hormone content of plants indicated elevated levels of the plant defense hormone jasmonic acid (JA) and its bioactive conjugate JA-Ile although significant differences were not observed. Conversely, the precursor to JA, 12-oxo-phytodienoic acid (OPDA) levels were significantly different between FAW fed Summer and Kanlow plants raising the possibility of differential signaling by OPDA in the two cultivars. Global transcriptome responses suggested a stronger response in Kanlow plant relative to Summer plants. Among these changes were a preferential upregulation of several branches of terpenoid and phenylpropanoid biosynthesis in Kanlow plants suggesting that enhanced biosynthesis and/or accumulation of antifeedants could have negatively impacted FAW larval weight gain on Kanlow plants relative to Summer plants. A comparison of Switchgrass-FAW RNA-Seq dataset to those from maize-FAW and switchgrass-aphid interactions revealed that key components of plant responses to herbivory, including induction of JA biosynthesis, key transcription factors and JA-inducible genes were apparently conserved in switchgrass, maize, and Arabidopsis. In addition, these data affirm earlier studies with FAW and aphids that the cultivar Kanlow can provide useful genetics for the breeding of switchgrass germplasm with improved insect resistance.