Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/25/2005
Publication Date: 3/2/2005
Citation: Zhang, A., Hartung, J.S. 2005. Phenylacetaldehyde o-methyloxime: a volatile compound from plants infected with citrus canker pathogenic bacterium, xanthomonas axonopodis pv. citri.. Journal of Agricultural and Food Chemistry. 53:5134-5137. Interpretive Summary: Citrus bacterial canker disease (CBCD) is caused by the plant pathogenic bacterium Xanthomonas axonopodis pv. citri. The disease weakens trees by causing cankers on branches and leaves of trees, and can spread rapidly by wind-driven rain. Because CBCD, countries or regions where the disease occurs may not export fresh fruit to countries where the disease does not occur. In order to protect Florida’s $10 billion citrus industry, there were two eradication campaigns in Florida in the 1980’s directed against this disease, and currently $40 million annually is being spent in Florida to eliminate the pathogen from residential neighborhoods in South Florida. At the present time, detection of CBCD is based on visual inspection and isolation of the bacterium in vitro. These methods are labor intensive and take days to complete. Therefore, easy, simple, and specific detection methods are urgently needed. We have developed a method that can detect a specific odor from grapefruit leaves infected by the CBCD pathogen. The method is rapid, simple, and accurate. This research may result in a diagnostic compound and may provide an easy and feasible tool to complement current inspection methods. It may be used by regulatory officials, such as Animal and Plant Health Inspection Service, and growers for detection of the CBCD to facilitate eradication campaign against this disease in Florida.
Technical Abstract: An aldehyde oxime o-methyl ether, phenylacetaldehyde o-methyloxime (PAAMO), 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. PAAMO 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. We conclude that PAAMO may potentially be used to identify CBCD infestations. However, more intensive studies will be required to fully evaluate the potential of PAAMO as a diagnostic compound. Using SPME and GC-MS to measure PAAMO may provide an easy and feasible tool to complement current methods used to detect X. axonopodis pv. citri in environmental samples.