In vitro Effect of Essential Oil of Peppermint (Mentha x piperita L.) on the Mycelial Growth of Alternaria alternata

Aims: The research aimed to evaluate the in vitro antifungal effect of the essential oil of peppermint (Mentha x piperita L.) in the control of Alternaria alternata. Study Design: The experiment was conducted in a completely randomised experimental design with five treatments in four replicates each. Place and Duration: The work was conducted at the Center of Science and Technology Agri-food of the Federal University of Campina Grande, Pombal-PB, Brazil, between February and March of 2018. Methodology: The essential oil was added to the PDA culture medium (Potato-Dextrose-Agar) autoclaved and subsequently poured into Petri plates. The treatments comprised five concentrations of the oil (0.0, 0.4, 0.6, 0.8, and 1.0%). After the inoculation with fungi, the plates were incubated for 14 days in a B.O.D incubator at 27±2°C. With the data of mycelial diameters, the percentage of mycelial growth inhibition (PGI) and index of mycelial growth speed (IMGS) were calculated. Results: All concentrations of peppermint oil reduced the mycelial growth of A. alternata. The minimum and maximum inhibitions occurred in the concentrations of 0.4 and 0.8%, which reached -13.27 and 72.45%, respectively. Although the maximum inhibition was 72.45%, the average percentages were 41.67 and 37.18% at the highest concentrations, showing an intermediate power of inhibition. A dose-dependent behaviour, was observed which suggests that further increases in concentration may enhance the inhibition effect of the oil. Conclusion: The peppermint oil can be used as a viable and sustainable antifungal product in the control of this pathogen. Due to the possible dose-dependent effect, the development of studies is recommended with concentrations around 2.25% to test if the oil reaches the total inhibition. The in vivo experiments are required to verify the oil feasibility on the control of A. alternata on plants and fruits.