Aspergillus section Nigri as contributor of fumonisin B₂ contamination in maize

Abstract

Fumonisins (FBs), which are carcinogenic mycotoxins, are known to be typically produced by several phytopathogenic fungal species belonging to the genus Fusarium. F. proliferatum and F. verticillioides, two important pathogens of maize worldwide, are the most common species that produce FBs. The main FBs produced by these species are FB₁, FB₂ and FB₃. Moreover, recently, fungal strains belonging to Aspergillus niger have been also reported to produce FBs (in particular, FB₂ and FB₄). In a survey on maize carried out in Central Italy, 17 maize kernel samples were collected at harvest and analysed for FB₁, FB₂ and FB₃, as well as fungal contamination, with a particular attention to the species-producing FBs. All 17 samples were contaminated by F. verticillioides and/or F. proliferatum at a level ranging from 13% to 100% of kernels. However, 10 out of 17 samples were also contaminated by Aspergillus section Nigri with a range from 6% to 68% of kernels. There was a significant inverse logarithmic relationship between levels of Fusarium and Aspergillus contamination. All samples were contaminated by FBs; FB₁ ranged from 0.09 to 30.2 μg g^–1, whereas FB₂ ranged from 0.04 to 13.2 μg g^–1. The ratio of FB₂/FB₁ contamination in the maize samples was evaluated and the highest values occurred in samples contaminated with Aspergillus section Nigri. Thirty strains of Aspergillus section Nigri isolated from these samples were molecularly identified (based on sequences of two housekeeping genes) and analysed for their capability to produce FB₂. Among the 30 strains isolated, 12 were identified as Aspergillus welwitschiae (syn. A. awamori) and 18 as A. tubingensis. FB₂ was produced by five out of 12 strains of A. welwitschiae within a range of 0.20–5 μg g^–1. This is the first report showing the capability of Aspergillus section Nigri from maize to produce FB₂ and its possibility to contribute to FB accumulation in kernels.

Keywords:

• fumonisins
• Aspergillus species
• mycotoxins
• feed safety

Acknowledgments

The authors thank Vincenzo Ricci and Sabrina Nocerino for valuable technical assistance.

Funding

This work was supported by EC KBBE-2007-222690-2 MYCORED.