Impact of cyanobacterial extracts on the growth and oil content of the medicinal plant Mentha piperita L.

Extracts of four heterocystous cyanobacteria isolated from wheat field soils (Triticum aestivum L.) were used as a promoter of growth and essential oil production in Mentha piperita L., which is mostly used for medicinal purposes. An axenic monoalgal culture was prepared using nitrate-free BG-11 medium. Pot experiments were performed by spraying algal extracts on the soil of treated plants on the first day of planting and every 20 days thereafter. Growth of plants was evaluated by measuring growth parameters such as plant height, root length, dry and fresh weight of plant, as well as leaf number, leaf area, and ramification after 100 days planting. In addition to growth factors, the quantity of essential oil of plants was also assessed. Statistical analysis showed that there were significant differences in the studied parameters compared to the control. The addition of some cyanobacterial inocula had a positive effect on the plant growth parameters and essential oil content. HPLC analysis of the cyanobacterial extracts detected some auxins, which may be the possible factor contributing to the positive growth responses and enhanced essential oil content of the treated plants.