Several species of Penicillium isolated from chestnut flour processing are pathogenic on fresh chestnuts and produce mycotoxins.

A collection of 124 isolates of Penicillium spp. was created by monitoring fresh chestnuts, dried chestnuts, chestnut granulates, chestnut flour and indoor chestnut mills. Sequencing of the ITS region, ß-tubulin and calmodulin, macro-morphology and secondary metabolite production made it possible to determine 20 species of Penicillium. P. bialowiezense was dominant in the fresh chestnuts, while P. crustosum was more frequent in the other sources. A pathogenicity test on chestnut showed that around 70% of the isolates were virulent. P. corylophilum and P. yezoense were not pathogenic, while the other 18 species had at least one virulent isolate. P. expansum and P. crustosum were the most virulent. The isolates were characterized to establish their ability to produce 14 toxic metabolites in vivo: 59% were able to produce at least one mycotoxin. P. expansum was able to produce patulin, chaetoglobosin A and roquefortine, while P. bialowiezense produced C. Mycophenolic acid. Cyclopenins and viridicatins were produced by most of the P. crustosum, P. polonicum, P. solitum and P. discolour isolates. Some of the P. crustosum isolates were also able to produce roquefortine C or penitrem A. Information about the occurrence of Penicillium spp. and their mycotoxins will help producers to set up management procedures that can help to control the fungal growth and the mycotoxin production of chestnuts.

Characterization of Aspergillus section Flavi isolated from fresh chestnuts and along the chestnut flour process.

An extensive sampling of Aspergillus section Flavi considered to be the main agent responsible for aflatoxin contamination, was carried out in the field and along the processing phases of chestnut flour production in 2015. Fifty-eight isolates were characterized by means of biological, molecular and chemical assays. The highest incidence of Aspergillus section Flavi was found in the field. The identification of the isolates was based on ß-tubulin and calmodulin gene sequences. A. flavus was found to be the dominant species, and this was followed by A. oryzae var effusus, A. tamarii, A. parasiticus and A. toxicarius. Nineteen percent of the strains produced aflatoxins in vitro and forty percent in vivo. The pathogenicity assay on chestnut showed 56 virulent strains out of 58. The molecular, morphological, chemical and biological analyses of A. flavus strains showed an intraspecific variability. These results confirm that a polyphasic approach is necessary to discriminate the species inside the Aspergillus section Flavi. The present research is the first monitoring and characterization of aflatoxigenic fungi from fresh chestnut and the chestnut flour process, and it highlights the risk of a potential contamination along the whole chestnut production chain.