Determination of flavonoid level variation in onion (Allium cepa L.) infected by Fusarium oxysporum using liquid chromatography–tandem mass spectrometry

Abstract

Abstract In order to evaluate the flavonoid level variation in an onion ( Allium cepa L.) infected by Fusarium oxysporum , the bulbs of a healthy onion and of an infected one were analysed for flavonoids via high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC–MS/MS). Among eleven flavonoids characterised, isorhamnetin 4′- O -galactoside ( 8 ) was identified in an onion for the first time. When the healthy bulb was inoculated with the fungus, the two quercetin derivatives ( 4 and 7 ) and the two isorhamnetin derivatives ( 5 and 9 ) underwent concentration changes typical for the defense materials against pathogens. The yellow granules that were accumulated on the abaxial epidermal cell layers after 8 days of inoculation were confirmed as quercetin ( 10 ) and isorhamnetin ( 11 ). It was deduced that they were produced from flavonoids 4 , 5 , 7 and 9 by hydrolysis enzyme of the fungus.