title: Application of glycerol as a foliar spray activates the defence response and enhances disease resistance of Theobroma cacao.
abstract: Previous work has implicated glycerol-3-phosphate (G3P) as a mobile inducer of systemic immunity in plants. We tested the hypothesis that the exogenous application of glycerol as a foliar spray might enhance the disease resistance of Theobroma cacao through the modulation of endogenous G3P levels. We found that exogenous application of glycerol to cacao leaves over a period of 4 days increased the endogenous level of G3P and decreased the level of oleic acid (18:1). Reactive oxygen species (ROS) were produced (a marker of defence activation) and the expression of many pathogenesis-related genes was induced. Notably, the effects of glycerol application on G3P and 18:1 fatty acid content, and gene expression levels, in cacao leaves were dosage dependent. A 100 mm glycerol spray application was sufficient to stimulate the defence response without causing any observable damage, and resulted in a significantly decreased lesion formation by the cacao pathogen Phytophthora capsici; however, a 500 mm glycerol treatment led to chlorosis and cell death. The effects of glycerol treatment on the level of 18:1 and ROS were constrained to the locally treated leaves without affecting distal tissues. The mechanism of the glycerol-mediated defence response in cacao and its potential use as part of a sustainable farming system are discussed.
authors.affiliation: The Huck Institute of the Life Sciences, The Pennsylvania State University, University Park, PA, 16802, USA; The Department of Plant Science, The Pennsylvania State University, University Park, PA, 16802, USA.
authors.forename: Yufan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Philip
authors.initials: P
authors.lastname: Smith
authors.forename: Siela N
authors.initials: SN
authors.lastname: Maximova
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Guiltinan
mesh_terms: D053898:Biosynthetic Pathways / Q000187:drug effects; D002099:Cacao / Q000187:drug effects / Q000235:genetics / Q000276:immunology* / Q000382:microbiology; D060467:Disease Resistance / Q000187:drug effects / Q000276:immunology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D005994:Glycerophosphates / Q000378:metabolism / Q000494:pharmacology*; D008315:Malondialdehyde / Q000378:metabolism; D019301:Oleic Acid / Q000378:metabolism; D010838:Phytophthora / Q000187:drug effects / Q000502:physiology; D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology; D018515:Plant Leaves / Q000033:anatomy & histology / Q000187:drug effects*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D005994:Glycerophosphates; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D019301:Oleic Acid; D008315:Malondialdehyde; C029620:alpha-glycerophosphoric acid
keywords: PR genes; Phytophthora capsici; Theobroma cacao; disease resistance; glycerol application; oleic acid