Headspace Solid-Phase Microextraction and Gas Chromatography-Mass Spectrometry for Analysis of VOCs Produced by Phytophthora cinnamomi

Abstract

Volatile organic compounds (VOCs) from Phytophthora cinnamomi–infected lupin seedlings were collected by headspace solid-phase microextraction (HS-SPME). The sampling was done 28 to 44, 52 to 68, and 76 to 92 h after inoculation (HAI). The HS-SPME samples were analyzed by gas chromatography-flame ionization detector (GC-FID) to assess the differences in volatile compounds between the P. cinnamomi–infected lupin seedlings and the control. Three specific peaks were identified after 52 to 68 h with the infected lupin seedlings, at which time there were no visible aboveground symptoms of infection. Subsequently, the VOCs of five different substrates (V8A, PDA, lupin seedlings, soil, and soil + lupin seedlings) infected with P. cinnamomi and the corresponding controls were analyzed by gas chromatography-mass spectrometry (GC/MS). A total of 87 VOCs were identified. Of these, the five most abundant that were unique to all five inoculated substrates included: 4-ethyl-2-methoxyphenol, 4-ethylphenol, butyrolactone, phenylethyl alcohol, and 3-hydroxy-2-butanone. Therefore, these metabolites can be used as markers for the identification of P. cinnamomi in different growing environments. Some VOCs were specific to a particular substrate; for example, 2,4,6-rrimethyl-heptanes, dl-6-methyl-5-hepten-2-ol, dimethyl trisulfide, 6,10-dimethyl- 5,9-undecadien-2-ol, and 2-methoxy-4-vinylphenol were specific to P. cinnamomi + V8A; heptanes and 5-methyl-3-heptaneone were specific to P. cinnamomi + PDA; 3-methyl-1-butanol, ethyl acetate, 2-methyl-propanoic acid, ethyl ester, and ethyl ester 2-methyl-butanoic acid were specific to P. cinnamomi–inoculated lupin seedlings; and benzyl alcohol and 4-ethyl-1, 2-dimethoxybenzene were only detected in the headspace of inoculated soil + lupin seedlings. Results from this investigation have multiple impacts as the volatile organic profiles produced by the pathogen can be utilized as an early warning system to detect the pathogen from contaminated field soil samples. Data from this investigation have also illuminated potential metabolic pathways utilized by the oomycete during infection which may serve as potential targets for the development of specific control strategies.