Antifungal effect and mode of activity of zinc chloride against toxigenic fungus Aspergillus flavus

Fungal plant pathogens cause considerable losses in yield and quality of field crops worldwide. Under specific environmental conditions, many fungi, such as Aspergillus spp., produce mycotoxins while colonizing their host, which accumulate in human and animal tissues, posing a serious threat to consumer health. Extensive use of fungicides in crop protection has stimulated the emergence of acquired drug resistance in some plant and human fungal pathogens. The use of metal compounds as antimicrobial agents offers an alternative strategy for managing potentially resistant toxigenic fungi and reducing the required dosage of specific drugs. We investigated the effect of zinc chloride (ZnCl2) on Aspergillus flavus infection and aflatoxin biosynthesis in cereal grains (wheat and maize) and legume crops (groundnut and chickpea). Following ZnCl2 treatment, quantitative PCR analysis showed a significant decrease in fungal DNA content in cereal grain and legume samples contaminated with A. flavus. Chitin content was dramatically reduced in A. flavus as a result of ZnCl2 treatment, suggesting that the zinc compound acts by inhibiting the synthesis of chitin, a fungal cell-wall component. Moreover, 5 days of treatment with 10 mM ZnCl2 reduced aflatoxin production by A. flavus in the tested crops by up to 43 %, and 20 and 40 mM ZnCl2 showed 87.4 to 99.7 % inhibition of toxin synthesis. These findings were supported by quantitative real-time PCR analysis, showing downregulation of key genes involved in the aflatoxin-biosynthesis pathway under ZnCl2 treatment. Our results provide evidence for antifungal and antimycotoxigenic effects of ZnCl2 against the filamentous fungus A. flavus. Future application of these findings may enable sustainable use of the compound in agricultural settings, while reducing potential concerns over exposure to high doses of fungicides that are harmful to the environment.