Discrimination of Plant Volatile Signatures by an Electronic Nose: A Potential Technology for Plant Pest and Disease Monitoring

The volatile organic compounds (VOCs) profile emitted from plants often changes in response to environmental factors, and monitoring the change of such profiles could provide a nondestructive means of plant health measurement. An electronic nose (e-nose) was used to discriminate among VOC bouquets emitted by cucumber, pepper, and tomato leaves subjected to mechanical damage or pest and disease attacks compared with undamaged control leaves. Principle component analysis, discriminant function analysis, and cluster analysis were applied to evaluate the data. The results indicate that the e-nose can discriminate among VOCs from undamaged leaves of the three tested species. It can also discriminate undamaged and artificially damaged leaves of the same plant species. In cucumber, the e-nose can discriminate among VOCs emitted from control, artificially damaged, and spider-mite-infested leaves. It could also discriminate among VOCs emitted from control, artificially damaged, hornworm-damaged, and powdery-mildew-infected tomato leaves. The relationships between the changes in volatile signatures detected by the e-nose to changes in the underlying chemistry of plant VOC signatures in response to applied stresses were quantified by gas chromatography mass spectrometry. We conclude that the e-nose had genuine responses to changes in plant VOC signatures and can successfully discriminate them. These studies demonstrate the potential use of such e-nose technology as a real time pest and disease monitoring system in agricultural and horticultural settings.