Aflatoxin Contamination, Mycoflora Diversity, and the Toxigenic Potential of Aspergillus spp. Associated with Maize Seeds and their Products

Aflatoxins are naturally occurring mycotoxins that are virtually impossible to eradicate from food and animal feed, and therefore contribute to the widespread contamination of maize products. These toxins are highly dangerous fungal substances that cause acute and chronic toxicity in humans and livestock. In the present study, 32 samples of different maize products were collected from different locations in Tamil Nadu, India, during 2021-2022 to assess aflatoxin contamination. Only two samples were free from aflatoxin contamination, whereas the other 30 maize samples were contaminated with different types of aflatoxins. In addition, maize seeds were collected from 15 locations covering 10 districts of Tamil Nadu, India, to study the mycoflora diversity. The results revealed the six main fungal genera, namely Aspergillus, Fusarium, Penicillium, Rhizopus, Alternaria, and Macrophomina, associated with maize seeds. Out of the 1152 mycoflora isolated from maize seeds, the genus Aspergillus contributed the most (82%), followed by Fusarium spp. (9%) and others (9%). Within the genus Aspergillus, A. niger, A. flavus, A. fumigatus, A. tamarii, and A. oryzae were recorded. Species composition studies revealed that A. niger, A. flavus and A. tamarii were present at all locations. Alpha diversity analysis of maize seed mycoflora and the genus Aspergillus using different indices revealed that abundance, dominance, and species richness were high at very few locations. Beta diversity analysis also revealed that there was no significant difference in the mycoflora between locations i.e. mycoflora distribution was even across all locations. Furthermore, the toxigenic potential of 24 Aspergillus isolates from different locations was assessed. The results revealed that the isolates Asp 16, Asp 17, Asp 20, and Asp 23 produced all four aflatoxins types, namely aflatoxin B1 (AFB1), aflatoxin B2 (AFB2), aflatoxin G1 (AFG1), and aflatoxin G2 (AFG2). Among the isolates, a maximum AFB1 of 10250.78 ppb/g of agar plug was recorded for the Asp 23 isolate, followed by Asp 20 (4246.584 ppb). Most isolates produced one or two aflatoxin types, and some non-toxigenic Aspergillus isolates were also recorded.