Aflatoxins (AFs) are secondary metabolites produced by Aspergillus section Flavi during their development, particularly in maize. It is widely accepted that AFB1 is a major contaminant in regions where hot climate conditions favor the development of aflatoxigenic species. Global warming could lead to the appearance of AFs in maize produced in Europe. This was the case in 2015, in France, when the exceptionally hot and dry climatic conditions were favorable for AF production. Our survey revealed AF contamination of 6% (n = 114) of maize field samples and of 15% (n = 81) of maize silo samples analyzed. To understand the origin of the contamination, we characterized the mycoflora in contaminated samples and in samples produced in the same geographic and climatic conditions but with no AFs. A special focus was placed on Aspergillus section Flavi. A total of 67 strains of Aspergillus section Flavi were isolated from the samples. As expected, the strains were observed in all AF+ samples and, remarkably, also in almost 40% of AF− samples, demonstrating the presence of these potent toxin producers in fields in France. A. flavus was the most frequent species of the section Flavi (69% of the strains). But surprisingly, A. parasiticus was also a frequent contaminant (28% of the strains), mostly isolated from AF+ samples. This finding is in agreement with the presence of AFG in most of those samples.

Aflatoxin B1 (AFB1) is a potent carcinogenic mycotoxin that contaminates numerous crops pre- and post-harvest. To protect foods and feeds from such toxins without resorting to pesticides, the use of plant extracts has been increasingly studied. The most interesting candidate plants are those with strong antioxidative activity because oxidation reactions may interfere with AFB1 production. The present study investigates how an aqueous extract of Mimosa tenuiflora bark affects both the growth of Aspergillus flavus and AFB1 production. The results reveal a dose-dependent inhibition of toxin synthesis with no impact on fungal growth. AFB1 inhibition is related to a down-modulation of the cluster genes of the biosynthetic pathway and especially to the two internal regulators aflR and aflS. Its strong anti-oxidative activity also allows the aqueous extract to modulate the expression of genes involved in fungal oxidative-stress response, such as msnA, mtfA, atfA, or sod1. Finally, a bio-guided fractionation of the aqueous extract demonstrates that condensed tannins play a major role in the anti-aflatoxin activity of Mimosa tenuiflora bark.

The worldwide distribution of aflatoxin B1, a carcinogenic mycotoxin, is changing due to climate change. This frequent contaminant of crops in tropical and subtropical regions is an emerging threat in Europe. Its first appearance in French maize was reported in 2015, a year with exceptional climatic conditions. But, from this year, such conditions (drought during spring and hot summers) occurred regularly, raising the question of a possible durable implantation of aflatoxigenic fungal species in French maize fields. To answer this question, 554 maize samples were collected during three consecutive years (2018–2020) throughout the French territory. They were subjected to mycological analysis and strains belonging to the Flavi section of the Aspergillus genus were identified, and their toxigenic potential was determined. This survey demonstrates that Aspergillus section Flavi are now frequent contaminants of maize since they were observed in more than 50% of samples in 2018 and 2019. This prevalence sharply increased in 2020 to reach 80% contamination. In parallel, the frequency of contamination with aflatoxins also increased. While it was very limited during the first two years of the study, despite favorable climatic conditions, contamination with aflatoxins was present in 16% of samples analyzed in 2020, exceeding E.U. regulation by 5%. Even if Aspergillus flavus is the dominant species, representing more than 90% of isolated strains, Aspergillus parasiticus seems to play a major role in grain contamination, as demonstrated by the presence of AFG in 50% of contaminated samples. These findings highlight the need to rethink the monitoring and management of aflatoxin risk in France for the future.