Efficacy and mechanism of Mentha haplocalyx and Schizonepeta tenuifolia essential oils on the inhibition of Panax notoginseng pathogens

In order to control the occurrence of Panax notoginseng (Burk.) F.H. Chen diseases, the antifungal effects and action mechanism of essential oils (EOs) against the pathogenic fungi were investigated. The antifungal effect of Mentha haplocalyx Briq. and Schizonepeta tenuifolia Briq. essential oils (EOs) were determined in vivo and in vitro to develop green fungicides to eradicate fungi pathogens affecting Panax notoginseng. The inhibition rates of M. haplocalyx and S. tenuifolia EOs (50 mg/mL) on Fusarium oxysporum, Fusarium solani, Cylindrocarpon destructans, Pythium aphanidermatum, Botrytis cinerea, Colletotrichum gloeosporioides and Rhizoctonia solani reached 100.00 % and were assessed by the Oxford cup method. The chemical constituents of M. haplocalyx and S. tenuifolia EOs were analyzed by GC–MS. Low MIC values of M. haplocalyx EO, S. tenuifolia EO and its main components against six fungal strains from P. notoginseng were found, which indicated all have substantial antifungal activity. Furthermore, synergistic effects between the EOs and the agrochemical hymexazol against P. notoginseng pathogens were observed. F. oxysporum was chosen as dominant fungi pathogen to investigate the mechanism of action of M. haplocalyx EO. The antifungal effect of M. haplocalyx EO on F. oxysporum in vitro was investigated. The high M. haplocalyx EO concentrations inhibited the spore germination rates, mycelia dry weights and spore yields and disturbed the mycelia soluble protein and reducing sugar contents; it also increased the cell membrane permeability. M. haplocalyx EO also induced decreased SDH and NADH oxidase activities and caused extreme alterations in ultrastructures compared with the control. Altogether, the antifungal mechanism of M. haplocalyx EO may seemed to consist in penetrating and dissolving the mitochondrial membranes. Overall, M. haplocalyx EO and its major compounds show potential to be used as natural alternatives to commercial fungicides for controlling F. oxysporum infection of P. notoginseng.