Abstract:In order to explore the natural antifungal agent of controlling banana anthracnose, antifungal activity of Isodon serra extract against Colletotrichum musae was evaluated by inhibition of mycelia growth and controlling activity test on banana fruits, and the potential mechanisms were investigated by studying the effect of I. serra extract on the mycelia cell integrity, mycelia morphology and activity of enzyme related to energy metabolism. The results showed that ethanol extract of I. serra and its different polar solvent extraction fractions had obvious antifungal activity against C. musae. Among them, petroleum ether fraction had the strongest inhibitory ability, its medium inhibitory concentration on mycelia growth was 0.18 mg/mL. The test of controlling activity on banana anthracnose showed that different concentrations of petroleum ether fraction decreased the lesion diameter of banana significantly compared with the control group (P<0.05), and the lesion diameter of banana treated with the extract at 4 mg/mL had no significant difference with the positive control (P>0.05). The integrity of C. musae mycelia cell was damaged significantly after incubation with the petroleum ether fraction, leading to the increase of cell permeability, moreover, the plasmolysis, shrinkage and crack in mycelia were also observed, and the damage degree was concentration-dependent. The enzyme activities of succinate dehydrogenase, malate dehydrogenase, ATP synthase and ATPase decreased by 23.56%, 60.51%, 9.01% and 32.01% respectively with the petroleum ether fraction treatment. In conclusion, these findings suggest that the antifungal mechanisms of I. serra extract against C. musae could be attributed to the disruption of cell structure and the effect on enzyme activities related to energy metabolism. Isodon serra extract could be used as a potential fungicide of controlling banana anthracnose.
