BIOLOGIA PLANTARUM 63: 690-698, 2019 DOI: 10.32615/bp.2019.139 690 Application of sodium salicylate up-regulates defense response against Fusarium graminearum in wheat spikes M. SORAHINOBAR 1 , V. NIKNAM 1,5 *, A. JAHEDI 2 , H. EBRAHIMZADEH 1 , B. MORADI 1 , M. BEHMANESH 3 , and H. SOLTANLOO 4 Department of Plant Biology, School of Biology, College of Science, University of Tehran, 1417466191, Tehran, Iran 1 Department of Plant Pathology, Tarbiat Modares University, 1411713116, Tehran, Iran 2 Department of Genetic, School of Biological Sciences, Tarbiat Modares University, 1411713116, Tehran, Iran 3 Department of Plant Breeding and Biotechnology, Gorgan University of Agricultural Sciences and Natural Resources, 4918943464, Gorgan, Iran 4 Center of Excellence in Medicinal Plant Metabolites, Tarbiat Modares University, 1411713116, Tehran, Iran 5 Abstract Fusarium head blight caused by the hemibiotrophic fungus Fusarium graminearum is one of the most devastating diseases of wheat which reduces both grain yield and quality. To better understand mechanism underlying wheat resistance to this pathogen, the expressions of five candidate genes encoding phenylalanine ammonia-lyase (PAL), glucanase-2 (Gl 2), class IV chitinase (Cht-4), cytochrome P 450 (CYP ) , and pleiotropic drug resistance (PDR) following spike inoculation with F. graminearum was compared in susceptible cv. Falat and resistant cv. Sumai3 at three time points (48, 96, 144 h after inoculation). Real-time quantitative PCR analysis indicated earlier and greater inductions of PAL, Glu-2, and Cht-4 in spikes of ‘Sumai3’ as compared to ‘Falat’ in response to F. graminearum inoculation. The expression of CYP in the resistant ‘Sumai3’ was about three times higher than in ‘Falat’ at 144 h after pathogen inoculation. Moreover, soil drench application of sodium salicylate (SA) one day before pathogen inoculation drastically curtailed pathogen infection in both the cultivars. Furthermore, SA treatment caused an induction of these genes in spikes of the susceptible cultivar to show a similar pattern as in the resistant one when inoculated with F. graminearum. Proteomics analysis of F. graminearum treated spikes 96 h after inoculation confirmed an increase of Glu and Cht spot volume in ‘Sumai3’ whereas a decrease in ‘Falat’. The SA treatment also caused significant increases in Glu and Cht spot volumes in both the cultivars. Our findings show an association between SA improvement of wheat defense against F. graminearum infection and induction of genes encoding proteins involved in pathogen response (Glu-2, Cht-4), secondary metabolite biosyntheses (PAL), and xenobiotic detoxification (CYP and PDR). Additional key words: Cht-4, CYP, fusarium head blight, Glu-2, resistance, PAL, PDR, Triticum aestivum. Submitted 19 September 2015, last revision 1 April 2019, accepted 16 April 2019. Abbreviations: Cht-4 - class IV chitinase; CYP - cytochrome P450;hai - hours after inoculation; DON - deoxynivalenol; FHB - fusarium head blight; Glu - glucanase-2; MPR - multidrug resistance-associated protein; PAL - phenylalanine ammonia-lyase; PAMP - pathogen associated molecular pattern; PDR - pleiotropic drug resistance; PR - pathogenesis-related; SA - sodium salicylate. Acknowledgements: We are most grateful to Dr. Ralph Kissen from the Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway and Prof. Jyoti Shah from the Department of Biological Science, University of North Texas, USA for the constructive comments and English language editing. * Corresponding author; e-mail: vniknam@khayam.ut.ac.ir This is an open access article distributed under the terms of the Creative Commons BY-NC-ND Licence Introduction Plants have evolved complex defense strategies to confront pathogen invasion. Based on the way that pathogens are detected by plants, there is a two-branched innate immune system: pathogen associated molecular pattern (PAMP)- triggered immunity (formerly called basal resistance) and effector-triggered immunity (formerly termed gene mediated resistance) (Jones and Dangl 2006). Both PAMP- triggered immunity and effector-triggered immunity can trigger salicylic acid accumulation, expression of pathogenesis-related (PR) genes, and systemic acquired resistance, which provides protection against a broad range of pathogens (Dempsey et al. 2011). A number of studies indicated that salicylic acid signaling pathway is required for resistance against biotrophic and hemi-biotrophic