Optimization of the Headspace Solid-Phase Microextraction Gas Chromatography for Volatile Compounds Determination in Phytophthora Cinnamomi Rands

Phytophthora cinnamomi (P. c) is a plant pathogenic oomycete that is capable of damaging plants in commercial production systems and natural ecosystems worldwide. The most common methods for the detection and diagnosis of P. c infection are expensive, elaborate and time consuming. This study was carried out to examine whether species specific and life cycle specific volatile organic compounds (VOCs) can be absorbed by solid-phase microextraction fibers and detected by gas chromatography that are produced by P. c and another oomycete Pythium dissotocum. A headspace solid-phase microextraction (HS-SPME) together with gas chromatography (GC) method was developed and optimized for the identification of the VOCs released by P. c. The optimized parameters included type of fiber, exposure time, desorption temperature and desorption time. Optimization was achieved with the analytes of P. c+V8A and V8A alone. To perform the HS-SPME, six types of fiber were assayed and compared: 7μm Polydimethylsiloxane (PDMS), 100μm Polydimethylsiloxane (PDMS), 50/30μm Divinylbenzene/Carboxen/Polydimethylsiloxane DVB/CAR/PDMS), 65μm Polydimethylsiloxane/Divinylbenzene (PDMS/DVB), 85μm Polyacrylate (PA) fibre and 85μm Carboxen/ Polydimethylsiloxane (CarboxenTM/PDMS). In a comparison of the efficacy of the fibers, the bipolar fiber DVB/CAR/PDMS had a higher extraction efficiency than the other fibers. An exposure time of 16h with DVB/CAR/PDMS fiber in the sample headspace was enough to reach the maximum extraction efficiency. A desorption time of 3min in the GC injector with the desorption temperature of 250°C was enough for the fiber to desorb the compounds of interest. The Rui Qiu is a student with the Plant Biosecurity Cooperative Research Centre, LPO Box 5012, Bruce, ACT 2617 and College of Environmental Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China (corresponding author to provide phone: 61-08-93606403; fax: 61-08-93606303; e-mail: R.qiu@ Murdoch.edu.au). Giles Hardy is with the Centre for Phytophthora Science and Management (CPSM), School of Biological Science and Biotechnology, Murdoch University, South Street, Murdoch, WA, 6150 Australia (e-mail: [email protected]). Dong Qu is with College of Environmental Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China (e-mail: [email protected]). Robert Trengove is with Separation Science and metabolomics Laboratory, Murdoch University, South Street, Murdoch, WA, 6150 Australia (e-mail: [email protected]/au). Manjree Agarwal is with the Plant Biosecurity Centre, LPO Box 5012, Bruce, ACT 2617 and School of Biological Science and Biotechnology, Murdoch University, South Street, Murdoch, WA, 6150 Australia (e-mail: [email protected]). Yonglin Ren is with the Plant Biosecurity Centre, LPO Box 5012, Bruce, ACT 2617, the School of Biological Science and Biotechnology, Murdoch University, South Street, Murdoch, WA, 6150 Australia and Department of Agriculture and Food, Western Australia, 3 Baron-Hay Court South Perth WA 6151 (e-mail: [email protected]). chromatograms and morphology study confirmed that the VOCs from P. c+V8A had distinct differences from V8A alone, as did different life cycle stages of P. c and different taxa such as Pythium dissotocum. The study proved that P. c has species and life cycle specific VOCs, which in turn demonstrated the feasibility of this method as means of identifying P. c. Keywords—Gas chromatography, headspace solid-phase microextraction, optimization, volatile compounds.