Early identification of fungal leaf blight disease (Alternaria alternate) on Platycladus orientalis plants by using gas chromatography-ion mobility spectrometry

Platycladus orientalis (L.) is a typical urban greening tree in Asia, but the young leaves of P. orientalis are   vulnerable to pathogenic fungi with hidden early   signs. In this study, we investigated the volatile organic compounds (VOCs) emissions of the Alternaria alternate infected P. orientalis plants, for the first time, using the gas chromatography-ion mobility spectrometry (GC-IMS) combined with chemometric approaches. Results showed that the A. alternate infection could reduce the VOCs release of P. orientalis leaves. The α-pinene and β-pinene emissions were down to 70% and 55% of controls on day 10, respectively. The destructive inoculated plants responded more to the A. alternate , both   in the VOCs emissions and the fungal growth. The (Z)-3-hexenol, n-hexanol, α-pinene, and β-pinene can serve as potential markers for infection discrimination, and their IMS signal intensities were calibrated with corresponding volume concentrations ranging from 0 to 250 μg/L. The PLS-DA model based on GC-IMS fingerprints can correctly classify at least 83% of samples in infection durations after fungal inoculation for the first 10 days. The PLSR model can predict the fungal colony counts in the P. orientalis needles (R c 2 ＞0.97 and R p 2 ＞0.92) with good robustness, whose RMSEP was lower than 0.68 (×10 6 CFU g −1 ) in predict set. In a word, the GC-IMS-based approach had the potential to evaluate A. alternate infection in P. orientalis , and the variation of potential markers can provide reference to its fungal infection monitor with   millisecond response in the forest.