Ageratum conyzoides essential oil as aflatoxin suppressor of Aspergillus flavus

Aflatoxin B1 (AFB1) is a highly toxic and carcinogenic metabolite produced by Aspergillus species on food and agricultural commodities. Inhibitory effects of essential oil of Ageratum conyzoides, on the mycelial growth and aflatoxin B1 production by Aspergillus flavus were studied. Cultures were incubated in yeast extract-sucrose (YES) broth for days at 25 °C at the following different concentrations of the essential oil (from 0.0 to 30 μg/mL). The essential oil inhibited fungal growth to different extents depending on the concentration, and completely inhibited aflatoxin production at concentrations above 0.10 µg/mL. The analysis of the oil by GC/MS showed that its main components are precocene II (46.35%), precocene I (42.78%), cumarine (5.01%) and Trans-caryophyllene (3.02%). Comparison by transmission electron microscopy of the fungal cells, control and those incubated with different concentrations of essential oil, showed ultra-structural changes which were concentration dependent of the essential oil of A. conyzoides. Such ultra-structural changes were more evident in the endomembrane system, affecting mainly the mitochondria. Degradation was also observed in both surrounding fibrils. The ability to inhibit aflatoxin production as a new biological activity of A.conyzoides L. indicates that it may be considered as a useful tool for a better understanding of the complex pathway of aflatoxin biosynthesis.