Volatile organic compound (VOC) profiling of citrus tristeza virus infection in sweet orange citrus varietals using thermal desorption gas chromatography time of flight mass spectrometry (TD-GC/TOF-MS)
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Citrus tristeza virus (CTV) (genus Closterovirus) is a plant pathogen which infects economically important citrus crops such as sweet oranges, mandarins, limes and grapefruit varietals. Within the last 70 years, an estimated 100 million citrus trees have been destroyed due to CTV infection worldwide. Present measures to contain CTV infection include scouts for visual assessment, and molecular analysis methods such as enzyme linked immunosorbent assay and reverse transcription polymerase chain reaction. Volatile organic compound (VOC) profiling may offer an alternative method of disease detection. In this study, we used a “Twister™” sorbent system for in-field VOC sampling. Chemical analysis was performed with thermal desorption gas chromatography time-of-flight mass spectrometry, and data were subjected to unsupervised and supervised analysis. Samples were collected from healthy trees, those with asymptomatic CTV, and those with CTV that were coinfected with a secondary unrelated bacterial infection of Spiroplasma citri, the causal agent of citrus stubborn disease (Stubborn). A total of 383 VOCs were detected across three classes: healthy control trees, CTV infected, and CTV coinfected with Stubborn. Mathematical models of this data were built to successfully differentiate: (a) healthy trees from CTV infected trees; (b) healthy trees from both CTV and CTV coinfected with Stubborn; and (c) to effectively differentiate between healthy trees and CTV infected trees, without consideration of Stubborn coinfection (the model would work on both singly or coinfected trees). The putative CTV biomarkers observed were terpenoid based (myrcene, carene, ocimene, bulnesene), two alcohols (n-undecanol, surfynol) and two acetones (geranyl acetone and neryl acetate).
KeywordsVolatile organic compounds (VOCs) Citrus tristeza virus (CTV) Mass spectrometry Gas chromatography Biomarker discovery
This manuscript is based upon work supported by the California Citrus Research Board (CED, OF, AMD), the Industry-University Cooperative Research Program (CED, OF, AMD), the Florida Citrus Production Advisory Council (CED), the National Science Foundation MCB 1139644 (OF) and the National Institute of Food and Agriculture (RKY). Student support was partially provided by the US Department of Veterans Affairs, Post-9/11 G.I. Bill (DJP). The research was supported by UC ANR at Lindcove Research and Extension Center (Exeter, CA). Opinions expressed in this publication are those of the authors and do not necessarily reflect the view of the funding agencies. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.
Compliance with ethical requirements
All authors confirm that they have adhered to all required ethical standards for this research.
Conflict of interest
Authors William H. K. Cheung, Alberto Pasamontes, Daniel J. Peirano, Weixiang Zhao, Abhaya M. Dandekar, Oliver Fiehn and Cristina E. Davis performed initial work on plant VOC biomarkers of citrus infection that pre-dated this manuscript, and they have a patent pending noting the identity of potential CTV-related VOC biomarkers (#WO2012129341 A2; priority filing date 21MAR2011).
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