Antifungal mode of action of bay, allspice, and ajowan essential oils and their constituents against Colletotrichum gloeosporioides via overproduction of reactive oxygen species and downregulation of ergosterol biosynthetic genes

This study was conducted to investigate the antifungal activity of 135 plant essential oils (EOs) and their constituents against Colletotrichum gloeosporioides (Penz.) Penz. and Sacc. Among the EOs, bay (Pimenta racemosa), allspice (Pimenta dioica), and ajowan (Trachyspermum ammi) showed 100 % inhibition of C. gloeosporioides at 10, 5, and 5 μl/paper disc, respectively. Of their constituents, (-)-α-pinene, (+)-α-pinene, thymol, eugenol, isoeugenol, 4-allylphenol, and carvacrol exhibited 100 % inhibition of growth at 10, 10, 10, 5, 5, 2.5, and 1.25 μl/paper disc, respectively. In an antifungal bioassay of artificial blends, eugenol, 4-allylphenol, and thymol were determined to be the major contributors to the antifungal activity of bay, allspice, and ajowan EOs. Confocal laser scanning microscopy images indicate the overproduction of reactive oxygen species (ROS) and cell membrane disruption in C. gloeosporioides treated with the EOs or their constituents. In addition, a decrease in ergosterol content and downregulation of ergosterol biosynthetic genes were confirmed in treated C. gloeosporioides. Based on these results, we attribute the antifungal actions of bay, allspice, and ajowan EOs and their active constituents to ROS generation and downregulation of ergosterol biosynthetic genes.