|CHEUNG, WILLIAM - University Of California|
|ZHAO, WEIXIANG - University Of California|
|PASAMONTES, ALBERTO - University Of California|
|KAPAUN, THERESE - University Of California - Cooperative Extension Service|
|Yokomi, Raymond - Ray|
|SWE, MIMI - University Of California|
|FIEHN, OLIVER - University Of California|
|DAVIS, CRISTINA - University Of California|
Submitted to: Metabolomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2015
Publication Date: 5/11/2015
Citation: Cheung, W.H., Zhao, W., Pasamontes, A., Kapaun, T., Yokomi, R.K., Swe, M., Fiehn, O., Davis, C.E. 2015. Volatile Organic Compound (VOC) profiling of Citrus tristeza virus (CTV) infection in sweet orange citrus varietals using thermal desorption gas chromatography time of flight mass spectrometry (TD-GC/TOF-MS). Metabolomics. doi: 10.1007/s11306-015-0807-6.
Interpretive Summary: Citrus tristeza virus (CTV) causes an economically important citrus disease and is spread by use of infected propagated trees and aphid vectors. Early detection will greatly improve disease management for CTV. To this end, an in-field, non-destructive device called “TwisterTM” sorbent system was developed to sample and trap volatile organic compounds (VOCs) emitted by the citrus leaf canopy surface. Biologically-generated VOCs in plants function to communicate between plants and from plants to animals. Trapped VOCs were released in the lab and chemically defined using a thermal desorption gas chromatography time of flight mass spectrometry (TD-GC/TOF-MS). Eighteen conserved VOC biomarkers were associated with asymptomatic CTV-infected trees and were not affected when the tree was co-infected by an unrelated bacterial pathogen, Spiroplasma citri, causal agent of citrus stubborn disease. VOC profiles successfully discriminated CTV-infected from CTV-free trees in two different citrus groves in central California. The VOC panel was validated statistically and was 90.9% accurate at detecting CTV-infected trees and 100% accurate in calls of CTV-free trees despite presence of citrus stubborn disease. Thus, VOC screening could be used to complement existing diagnostic tests for CTV.
Technical Abstract: Citrus tristeza virus (CTV) is a plant pathogen which predominately infects economically important citrus crops such as sweet orange, clementine, lime and grapefruit varietals. Within the last 70 years, an estimated 100 million citrus trees on sour orange rootstock have been destroyed due to CTV infection worldwide. Present measures to contain CTV infection include: insect traps and scouts for visual assessment, statistically valid surveys and tissue sampling from trees and analysis by ELISA and RT-PCR for CTV. Volatile organic compound (VOC) profiling may offer an alternative method of detecting diseased trees. In this study, a “TwisterTM” sorbent system was developed and used for in-field VOC sampling. VOC was released and chemical analysis was performed on a thermal desorption gas chromatography time of flight mass spectrometry (TD-GC/TOF-MS). Data were subjected to supervised and unsupervised analysis. This method successfully discriminated asymptomatic CTV infected trees from healthy controls trees in citrus orchards even when the tree was dually infected by CTV and Spiroplasma citri, causal agent of citrus stubborn disease. A total of 383 common VOCs were detected across three classes: CTV infected, CTV co-infected with stubborn disease, and uninfected control trees. Of these, 18 conserved VOC biomarkers were associated with asymptomatic CTV infections and were not affected by co-infection by S. citri. The robust discriminatory capability of this VOC panel was quantitatively assessed using partial least square regression (PLSR), and the final model resulted in correct classification of 90.9% for CTV infected trees and 100% for CTV-free trees. Thus, VOC screening could be used to complement existing testing for CTV detection and other citrus pathogens.