The effects of some essential oils on Alternaria alternata , a post-harvest phyto-pathogenic fungus in wheat by disrupting ergosterol biosynthesis

Foods contaminated with fungi and their toxins cause many infections in developing and underdeveloped countries. Owing to the development of resistance by fungal pathogens to existing chemical antifungal agents, there is an urgent need to look for new eco-friendly antimicrobial agents. There is an increasing demand from agro-food industries for new environmentally compatible fungicides. Plant essential oils are an excellent source of antifungal volatile substances which are appropriate substitutes for food protection. Keeping this in mind we evaluated the efficacy of selected essential oils in suppressing the growth of Alternaria alternata isolated from stored wheat grains using in vitro and in vivo models. Preliminary antifungal activities varied among the tested oils with the zones of inhibition ranging from 10.66±1.15 mm to 19±1.00 mm. Among the tested oils T. asiatica oil showed significant inhibitory effects on A. alternata at 2.5 µL/mL. Further, its mechanistic action was related to the impairment of the squalene gene (SqSy) which was involved in the biosynthesis of sterol and ergosterol membrane factors. This was further supported by altered sterol profile of A. alternata with 29.4±2.40% reduction of total ergosterol content at 30 µL/mL. Moreover, prolonged exposure to T. asiatica oil as a fumigant controlled the total fungal count up to 68.75% compared to the control for a period of 12 months. T. asiatica oil proved to be a promising candidate to control A. alternata and its mycotoxin residues in stored wheat. It can be used as a sustainable and effective alternative to develop new fungicide. Graphical abstract