Aspergillus section Flavi from chestnuts: biological, molecular and chemical characterization

Aspergillus section Flavi, and particularly Aspergillus flavus, are considered the main responsible for aflatoxin contamination along the chestnut production chain. During 2015, an extensive sampling of Aspergillus section Flavi from the field and throughout the processing phases of the chestnut flour production chain was carried out. Biological, molecular, and chemical assays were performed in order to characterize fifty-eight isolates. β-tubulin and calmodulin gene sequences were used to identify the isolates. The main species was A. flavus, followed by A. oryzae var. effusus, A. tamarii, A. parasiticus and A. toxicarius. By considering aflatoxins (AFs) production, 19% of the strains produced AFs in vitro and 40% in vivo. 56 out of 58 strains resulted virulent based on results from the pathogenicity assay. The A. flavus strains showed an intraspecific variability by molecular, morphological, chemical and biological analyses, confirming that a polyphasic approach is necessary to discriminate the species inside the section Flavi. The ability of the strains to produce AFs in vivo and the pathogenicity tests showed the potential contamination along the chestnut production chain. Guidelines to manage the aflatoxin risk should be developed for the chestnut chain, as common practices are not able to efficiently reduce the risk of contamination by aflatoxigenic fungi. This research represents the first characterization of aflatoxigenic fungi from fresh chestnut and the chestnut flour process