Effects of Phytophthora ramorum on volatile organic compound emissions of Rhododendron using gas chromatography-mass spectrometry

Authors: MCCARTNEY, MITCHELL - University Of California; ROUBTSOVA, TATIANA - University Of California; YAMAGUCHI, MEI - University Of California; Kasuga, Takao; EBELER, SUSAN - University Of California; DAVIS, CRISTINA - University Of California; BOSTOCK, RICHARD - University Of California

Submitted to: Analytical and Bioanalytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2017
Publication Date: 12/15/2017
Citation: McCartney, M., Roubtsova, T., Yamaguchi, M., Kasuga, T., Ebeler, S., Davis, C., Bostock, R. 2017. Effects of Phytophthora ramorum on volatile organic compound emissions of Rhododendron using gas chromatography-mass spectrometry. Analytical and Bioanalytical Chemistry. 410(5):1475-1487. https://doi.org/10.1007/s00216-017-0789-5.
DOI: https://doi.org/10.1007/s00216-017-0789-5

Interpretive Summary: Phytophthora ramorum is an invasive and devastating plant pathogen that causes sudden oak death in coastal forests in the western United States and ramorum blight in nursery ornamentals and native plants in various landscapes. As a broad host-range quarantine pest that can be asymptomatic in some hosts, P. ramorum presents significant challenges for regulatory efforts to detect and contain it, particularly in commercial nurseries. As part of a program to develop new detection methods for cryptic infections in nursery stock, we compared volatile emissions of P. ramorum-inoculated and noninoculated Rhododendron plants using gas chromatography-mass spectrometry methods. We have identified volatile chemical signatures unique to infected plants. Volatile detection techniques we developed could lead to innovative approaches that augment detection and diagnosis of P. ramorum and related oomycete pathogens in nurseries and other settings.

Technical Abstract: Phytophthora ramorum is an invasive and devastating plant pathogen that causes sudden oak death in coastal forests in the western United States and ramorum blight in nursery ornamentals and native plants in various landscapes. As a broad host-range quarantine pest that can be asymptomatic in some hosts, P. ramorum presents significant challenges for regulatory efforts to detect and contain it, particularly in commercial nurseries. As part of a program to develop new detection methods for cryptic infections in nursery stock, we compared volatile emissions of P. ramorum-inoculated and noninoculated Rhododendron plants using three gas chromatography-mass spectrometry methods. The first used a branch enclosure combined with headspace sorptive extraction to measure plant volatiles in situ. Seventy-nine compounds were found in the general Rhododendron profile; three were upregulated in healthy plants. The volatile profile of inoculated, but asymptomatic, plants (121 d post-inoculation) was distinguishable from the profile of the healthy noninoculated controls. A second method employed stir bar sorptive extraction to measure volatiles in vitro from leaf extractions in methanol; 115 volatiles were found in the overall profile with 30 compounds upregulated in healthy, noninoculated Rhododendron and one compound upregulated in inoculated Rhododendron. At 128 d post-inoculation, plants were asymptomatic and similar in appearance to the noninoculated controls, but their chemical profiles were different. In a third technique, volatiles from water runoff from the soil of potted healthy and inoculated Rhododendron plants were compared. Runoff from the inoculated plants emitted four unique volatile compounds that never appeared in the runoff from noninoculated plants. These three volatile detection techniques could lead to innovative approaches that augment detection and diagnosis of P. ramorum and related oomycete pathogens in nurseries and other settings.