Volatile metabolite profiling to discriminate diseases of McIntosh apple inoculated with fungal pathogens

Gas chromatography-mass spectrometry (GC/MS) technology was used to profile volatile metabolites from the headspace gas of McIntosh apple (Malus domestica Borkh.), which were non-inoculated or inoculated with four different fungi, Botrytis cinerea Pers, Penicillium expansum Link, Mucor piriformis Fischer and Monilinia sp. The study yielded a total of 498 different volatile metabolites. Among them only 35 occurred relatively consistently in six replicates over three incubation periods. Of the consistent metabolites, 20 were specific to one or more inoculation agents/diseases, including seven that were unique to apples inoculated with different pathogens. Fluoroethene and 3,4-dimethyl-1-hexene were specific for Penicillium, while butanoic acid butyl ester, 4-methyl-1-hexene and 2-methyltetrazole were specific for Mucor. Similarly, acetic acid methyl ester and fluoroethane were specific to Botrytis and Monilinia, respectively. The method developed in this study can be used by storage managers to detect apple diseases at an early stage of disease progress and use this to manage apple diseases in storage, after further validation under commercial conditions.