Black mould rot caused by black Aspergilli is an important post-harvest disease of onion worldwide. Usually Aspergillus niger is cited as the causative agent based on morphological criteria. In this study, the mycobiota and fumonisin contamination of mouldy onion bulbs purchased in Hungary were examined. All except one of the examined mouldy samples were found to be contaminated with black Aspergilli, which could be isolated both from the outer dry and the inner fleshy scales of onion bulbs. Species assignment of the isolates was carried out using sequence analysis of part of the calmodulin gene. Sequence data revealed that all 35 black Aspergilli isolated from onions belong to the Aspergillus awamori species. The range of fumonisin isomers present in the onion samples was also examined using reversed-phase high-performance liquid chromatography/electrospray ionization-ion trap mass spectrometry. Two of the examined onion samples were found to be contaminated with fumonisins at a rate of about 0.3 mg kg-1. This is the first report on fumonisin contamination of onion bulbs. The fumonisin isomers observed include fumonisins B2-4, 3-epi-FB4, iso-FB1 (FB6) and an iso-FB2,3 form. The range of fumonisin isomers detected in the onion bulbs indicates that probably A. awamori is responsible both for mould rot and fumonisin contamination of onions in Hungary.
ASJC Scopus subject areas
- Food Science