Headspace volatile organic compounds as indicators of Fusarium basal plate rot and Penicillium rot in stored onion bulbs

Food loss is a global problem, and one important contributor is the pathogen-induced loss of crops during storage in the supply chain. This could be countered by monitoring systems, including ones that monitor the release of volatile organic compounds (VOCs) indicating pathogen infection. In order to study the release of VOCs from onion bulbs affected by Fusarium basal plate rot or Penicillium rot bulbs were infected with the causal agents Fusarium oxysporum , or Penicillium polonicum and emitted headspace VOCs were analysed using solid phase microextraction (SPME) and gas chromatography coupled with mass spectrometry (GC-MS). We identified headspace VOCs that mark onion bulbs with pathogen infection. Seven compounds were detected in F. oxysporum -infected but not in healthy bulbs: 1-(methylthio)-propane, dimethyl disulfide, ethenylbenzene, 2,2-bis(methylthio)-propane, 1-(methylsulfinyl)-propane and 2-(methylsulfonyl)-propane and methyl 1-propenyl disulfide. In the volatile profiles of P. polonicum -infected bulbs a few compounds, including 2,4-dimethyl-thiophene and 2-hexyl-5-methyl-3(2H)-furanone were found in increased abundance. Accelerated sprouting was seen in bulbs infected with P. polonicum , which may have affected the volatile profile. The demonstrated effect of fungal pathogens on the volatile profile of onion bulbs could prove useful in the future development of monitoring systems for early detection of rot in stored onions. • Fungal infection in onion caused changes to the headspace volatile fingerprint. • Several compounds were distinct to either Penicillium or Fusarium infection. • Potential for future early onion storage rot detection using VOC monitoring.