Marker Compounds of Microbial Infection in Allium cepa

Common onion (Allium cepa) is considered as one of the most important vegetables.¹ Some bacteria and fungi can infect the onion and spoil the bulbs within a short period of time.² The early stages of infection cannot be detected in onions by conventional analytical methods. It can be assumed that the pattern of chemical compounds is altered by the action of pathogenic bacteria and fungi. In this project, four types of microorganisms (Fusarium oxysporum, Fusarium proliferatum, Penicillium sp, Botrytis aclada) were tested in onion bulbs to elucidate and identify the volatile chemical markers after infection. Healthy and infected onion bulbs were extracted by ethyl acetate. The extracts have been analysed by HPLC to define the infection markers. Two different new peaks were identified in the chromatograms that can refer to marker compounds. Fractions were investigated to prove its chemical structure by HPLC/MS, NMR and HRMS. According to the obtained data, the two compounds are 2-hexyl-5-methyl-3(2 H)-furanone and 2-octyl-5-methyl-3(2 H)-furanone (Fig.). Because these compounds only occur after infection, they can be considered as infection markers.

[1] Keusgen M. Volatile Compounds of the Genus Allium L. (Onions). Marburg: University of Marburg; 2010: 2 – 3.

[2] Shrestha H. A Plant Monograph on Onion (Allium cepa L.). Nepal: Pokhara University; 2007: 31.