ORIGINAL ARTICLE 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) William H. K. Cheung 1 • Alberto Pasamontes 1 • Daniel J. Peirano 1 • Weixiang Zhao 1 • Elizabeth E. Grafton-Cardwell 2 • Therese Kapaun 2 • Raymond. K. Yokomi 3 • Jason Simmons 1 • Mimi Doll 4 • Oliver Fiehn 4 • Abhaya M. Dandekar 5 • Cristina E. Davis 1 Received: 14 October 2014 / Accepted: 8 May 2015 Ó Springer Science+Business Media New York 2015 Abstract Citrus tristeza virus (CTV) (genus Clos- terovirus) 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 im- munosorbent 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 TM ’’ 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 unsuper- vised 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 in- fected trees; (b) healthy trees from both CTV and CTV coinfected with Stubborn; and (c) to effectively differen- tiate 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, car- ene, ocimene, bulnesene), two alcohols (n-undecanol, sur- fynol) and two acetones (geranyl acetone and neryl acetate). Keywords Volatile organic compounds (VOCs) Á Citrus tristeza virus (CTV) Á Mass spectrometry Á Gas chromatography Á Biomarker discovery 1 Introduction Volatile organic compound (VOC) profiling is a novel field of chemical analysis, where the emitted volatiles contain important diagnostic information regarding host physio- logical health status in response to infection (Goff and Klee 2006). This has particular importance in high throughput precision agriculture and post-harvest applications, for real William H. K. Cheung and Alberto Pasamontes have contributed equally to this work and should be considered joint first authors. Electronic supplementary material The online version of this article (doi:10.1007/s11306-015-0807-6) contains supplementary material, which is available to authorized users. & Cristina E. Davis cedavis@ucdavis.edu 1 Department of Mechanical and Aerospace Engineering, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA 2 University of California, Lindcove Research and Extension Center (LREC), 22963 Carson Avenue, Exeter, CA 93221, USA 3 United States Department of Agriculture, Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Riverbend Avenue, Parlier, CA 93648, USA 4 University of California, Davis, Genome Center, Health Science Drive, Davis, CA 95616, USA 5 Department of Plant Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA 123 Metabolomics DOI 10.1007/s11306-015-0807-6