The endophytic fungus Serendipita indica is considered as one of the beneficial soil microorganisms, which by creating physiological changes in the host plants, affects their performance in relation to growth and tolerance to plant stresses. In this study, the effects of Serendipita indica (four levels of fungus including without fungus treatment, and 1, 2 and 3 pieces of fungus solid medium with dimensions of 0.2×1×1 cm) on growth parameters of peppermint were evaluated under without stress condition and lead stress (800 mg/kg soil). The results showed that lead reduced growth parameters including leaf number in plant, shoot height and root length. The use of endophyte fungus had positive effects on the parameters studied so that by increasing the amount of fungus in the soil, leaf number in plant, shoot height and root length were significantly increased. The highest amount of each growth index, both in plants under lead stress and in plants without lead stress, was observed at the highest level of the fungus in the soil. Using these results, it can be said that S. indica has increased growth indicators and significantly reduced the harmful effects of lead in medicinal plant peppermint.
