Evaluation of the effect of mycorrhizal fungus and zinc sulfate foliar application on some physiological and biochemical traits and economic yield of Hypericum perforatum L. under different irrigation regimes

St. John's wort (Hypericum perforatum L.) is a medicinal plant that is more than 2000 years old. Drought stress is one of the most limiting environmental factors in the growth and production of plants. Plant symbiosis with mycorrhiza fungi and foliar spraying of essential elements can be one of the most effective solutions to deal with drought stress. This research also aims to evaluate the effect of mycorrhizal fungus and zinc sulfate foliar spraying on some biochemical traits and economic yield in St. John's wort under different irrigation regimes in a split factorial experiment with a basic randomized complete block design in three repetitions carried out during the three cropping years of 2018, 2019 and 2020. The main factor is irrigation regimes at three levels (100, 75 and 50% of irrigation needs); sub-factors were ZnSO4 foliar spraying at three levels (0, 3 and 6 per thousand) and inoculation with an AMF (Funneliformis mosseae) at two levels (inoculated and uninoculated). The results showed that the triple interaction of irrigation regimes + foliar spraying + mycorrhiza in all three years had a significant effect on chlorophyll content, proline, soluble sugars, malondialdehyde and economic yield. Increasing irrigation stress had a reducing effect on chlorophyll content, economic yield, and the relative water content of leaves, but on proline, soluble sugars and malondialdehyde had an increasing effect. At each stress level, the highest economic yield was obtained in the treatment of 6 per thousand foliar spraying + inoculation with mycorrhizal fungi. Generally, foliar spraying of zinc sulfate + mycorrhiza increased the content of chlorophyll, sugar solvents and the relative water content of the leaf, caused the adjustment of the stress conditions and increased the resistance of the plant against drought, and by improving the quantitative and qualitative biochemical traits, it increased the economic yield of the St. John's wort plant.