title: Assessment of drought tolerance of 49 switchgrass (Panicum virgatum) genotypes using physiological and morphological parameters.
abstract: BACKGROUND
  Switchgrass (Panicum virgatum L.) is a warm-season C4 grass that is a target lignocellulosic biofuel species. In many regions, drought stress is one of the major limiting factors for switchgrass growth. The objective of this study was to evaluate the drought tolerance of 49 switchgrass genotypes. The relative drought stress tolerance was determined based on a set of parameters including plant height, leaf length, leaf width, leaf sheath length, leaf relative water content (RWC), electrolyte leakage (EL), photosynthetic rate (Pn), stomatal conductance (g s), transpiration rate (Tr), intercellular CO2 concentration (Ci), and water use efficiency (WUE).
  
  
  RESULTS
  SRAP marker analysis determined that the selected 49 switchgrass genotypes represent a diverse genetic pool of switchgrass germplasm. Principal component analysis (PCA) and drought stress indexes (DSI) of each physiological parameter showed significant differences in the drought stress tolerance among the 49 genotypes. Heatmap and PCA data revealed that physiological parameters are more sensitive than morphological parameters in distinguishing the control and drought treatments. Metabolite profiling data found that under drought stress, the five best drought-tolerant genotypes tended to have higher levels of abscisic acid (ABA), spermine, trehalose, and fructose in comparison to the five most drought-sensitive genotypes.
  
  
  CONCLUSIONS
  Based on PCA ranking value, the genotypes TEM-SEC, TEM-LoDorm, BN-13645-64, Alamo, BN-10860-61, BN-12323-69, TEM-SLC, T-2086, T-2100, T-2101, Caddo, and Blackwell-1 had relatively higher ranking values, indicating that they are more tolerant to drought. In contrast, the genotypes Grif Nebraska 28, Grenville-2, Central Iowa Germplasm, Cave-in-Rock, Dacotah, and Nebraska 28 were found to be relatively sensitive to drought stress. By analyzing physiological response parameters and different metabolic profiles, the methods utilized in this study identified drought-tolerant and drought-sensitive switchgrass genotypes. These results provide a foundation for future research directed at understanding the molecular mechanisms underlying switchgrass tolerance to drought.
authors.affiliation: Department of Crop and Soil Environmental Science, Virginia Tech, 367 Smyth Hall, 185 Ag Quad Ln, Blacksburg, VA 24061 USA.
authors.forename: Yiming
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Crop and Soil Environmental Science, Virginia Tech, 367 Smyth Hall, 185 Ag Quad Ln, Blacksburg, VA 24061 USA.
authors.forename: Xunzhong
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Statistics, Virginia Tech, Blacksburg, VA USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Tran
authors.affiliation: Department of Statistics, Virginia Tech, Blacksburg, VA USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Shan
authors.affiliation: Department of Plant Biology, Michigan State University, East Lansing, MI USA.
authors.forename: Jeongwoon
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Plant Biology, Michigan State University, East Lansing, MI USA ; Center for Genomics-Enabled Plant Science, Michigan State University, East Lansing, MI USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: Childs
authors.affiliation: Department of Crop and Soil Environmental Science, Virginia Tech, 367 Smyth Hall, 185 Ag Quad Ln, Blacksburg, VA 24061 USA.
authors.forename: Erik H
authors.initials: EH
authors.lastname: Ervin
authors.affiliation: Department of Horticulture, Virginia Tech, 407 Latham Hall, 220 Ag Quad Ln, Blacksburg, VA 24061 USA.
authors.forename: Taylor
authors.initials: T
authors.lastname: Frazier
authors.affiliation: Department of Horticulture, Virginia Tech, 407 Latham Hall, 220 Ag Quad Ln, Blacksburg, VA 24061 USA.
authors.forename: Bingyu
authors.initials: B
authors.lastname: Zhao
keywords: Drought tolerance; Genetic diversity; Germplasm; Metabolites; PCA; Panicum virgatum; SRAP marker