Phenylacetaldehyde O-methyloxime: a Volatile Compound Produced by Grapefruit Leaves Infected with the Citrus Canker Pathogen, Xanthomonas Axonopodis Pv. Citri

An aldehyde oxime O-methyl ether, phenylacetaldehyde O-methyloxime, was detected using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) in the headspace above grapefruit leaves infected with Xanthomonas axonopodis pv. citri, the causal agent of citrus bacterial canker disease (CBCD). This disease is a major phytosanitary concern, and an eradication campaign against it is currently underway in Florida. Phenylacetaldehyde O-methyloxime has been reported to be produced by other plants and fragrant flowers, but it was not observed in the headspace above uninfected grapefruit leaves, the pathogenic bacterium X. axonopodis pv. citri itself, or grapefruit leaves infected with another closely related bacterial pathogen, X. axonopodis pv. citrumelo, which causes citrus bacterial spot, a disease of no phytosanitary significance. It was also not detected from CBCD infected fruits, including orange, lemon, grapefruit, and lime. We conclude that phenylacetaldehyde O-methyloxime may potentially be used to identify CBCD infestations. However, more intensive studies will be required to fully evaluate the potential of phenylacetaldehyde O-methyloxime as a diagnostic compound for CBCD. Using SPME and GC-MS to measure phenylacetaldehyde O-methyloxime may provide an easy and feasible tool to complement current methods used to detect X. axonopodis pv. citri in environmental samples.