Acetic acid and hydrogen peroxide improved defense-related biochemical responses of onion bulbs to black mold rot caused by Aspergillus niger L.

During field conditions and storage, onion bulbs are often severely affected by Aspergillus niger L., which leads to substantial yield and quality loss due to black mold. In the El-Minia region of Egypt, we isolated several strains of A. niger from different onion bulbs. To combat the black mold rot disease caused by A. niger, we tested the individual and combined effects of acetic acid and hydrogen peroxide against the most virulent strain under both in vitro and storage (180 days) conditions. Additionally, we measured the levels of antioxidant compounds such as phenolic acids, polyphenols, and ascorbic acid. Our pathogenicity tests helped us identify the most virulent isolate. We found that the environmentally friendly compound peroxyacetic acid, derived from the combination of hydrogen peroxide and acetic acid, reduced black mold infection in both, in vitro and storage conditions. Treating postharvest onion bulbs with 0.2 g L−1 acetic acid and 0.4 g L−1 hydrogen peroxide promised to mitigate the development of black mold rot for 180 days of storage. Furthermore, our results indicated that these treatments increased bioactive antioxidant compounds such as ascorbic acid, phenolic compounds, and polyphenols. These compounds, as secondary metabolites, served as the first line of defense against onion rot disease during storage. In conclusion, applying peroxyacetic acid proved a practical approach to controlling black mold rot disease development in onion bulbs during storage. [ABSTRACT FROM AUTHOR]