Finding the Markers of Fungal and Bacterial Infections in Allium cepa L.
Common onion (Allium cepa L.) is considered as one of the most important vegetables due to the extensive usage in industrial food production. The production of dried onions is more than 88 million tons every year. However, onions are prone to several microbial infections reducing their yield and qua...
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|Common onion (Allium cepa L.) is considered as one of the most important vegetables due to the extensive usage in industrial food production. The production of dried onions is more than 88 million tons every year. However, onions are prone to several microbial infections reducing their yield and quality within a short period. The early stages of infection cannot be detected in onions by the 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, we aim to identify the markers of infection in Allium cepa L. which can help to provide early detection of common onion diseases.
Five microbial strains including: Fusarium oxysporum, Fusarium proliferatum, Penicillium sp., Botrytis aclada, and Erwinia carotovora, were used to infect onion bulbs. Healthy and infected bulbs were extracted with ethyl acetate. The extracts have been analyzed using HPLC to define potential infection markers. Two new peaks were observed and suggested to be markers for the infections. Fractions were further investigated to charactarize their chemical structures by HPLC/MS, HRMS, UV, IR, and NMR. For the quantitative determination of both marker compounds, dimethyl dihydrofuranone (DMDHF) was served as an internal as well as external standard. Seven other Allium species were also studied to investigate the presence of the same markers. In addition, some experimental work was done to synthesize the markers and detect them using GC and IMS. The bioactivity of the new substances in infected onion extracts was also studied.
The structures of the two markers obtained after infection were confirmed as 2-hexyl-5-methyl-3(2H)-furanone and 2-octyl-5-methyl-3(2H)-furanone. These compounds could only be detected after infection, and they could be considered as markers of fungal and bacterial infections in Allium cepa L. The concentration of the markers varied between 1 and 30 ppm depending on the fresh mass of onions. The exact concentration might depend on the grade of infection. These investigated markers also appeared in A. altaicum Pall., A. . pskemense B. Fedt., A. cornutum Clementi ex Vis., A. fistulosum L., and A. porrum L., whereas they could not be detected in Allium sativum L. In bioactivity tests, no significant antifungal or antitumor activity could be recorded. The results showed also increases in free quercetin in infected onion bulbs in comparison to the healthy ones.
The 3(2H)-furanones have already been reported in previous studies as normal aroma substances located in Allium cepa. The production of 3(2H)-furanones in plants after infection could be an indirect defense strategy to confuse the quorum sensing in bacteria and other microorganisms.