Evaluation of plant growth promotion characteristics of endophytic bacteria isolated from leaves and stems of some medicinal plants

Medicinal plants have an important role in advancing national, regional and global goals for achieving health, drug self-sufficiency, employment creation and economic development. Since, quality and quantity improving of medicinal plants is aimed therefore it seems that the application of biofertilizers is the most compatible with that purpose. The objectives of this research were to isolate endophytic bacteria from leaves and stems of medicinal plants and to evaluate their growth promoting traits and assess their potential as biofertilizers. Healthy basil, rosemary, savory and pennyroyal plants were collected from area around Ardabil city and transferred to the laboratory. The endophytic bacteria isolated using serial dilution technique on the nutrient agar. Different colonies according to the appearance, color, margin and growth rate were selected, purified and kept at 4 °C. Then, the ability of the isolates to produce Indole Acetic Acid (IAA), solubilization of tricalcium phosphate, hydrogen cyanide and protease were evaluated. In this study, 99 endophytic bacteria were isolated from the medicinal plants. Finally, According to the morphological properties and growth rate, 53 different isolates (13 isolates from each plant) were selected. Results revealed that all the endophytic bacteria were able to produce IAA at 100 mg l-1 L-tryptophan. The most potent bacteria in terms of IAA production were p < sub>4, p < sub>3 and B1 isolates (with production of 15.31 mg l-1, 11.55 mg l-1 and 12.97 mg l-1, respectively). All of the examined isolates had the ability to dissolve tricalcium phosphate. The highest ability of solubility (646.52 mg l-1) was observed in S5 isolated from Savory. The bacteria isolated from Rosemary had the lowest ability to dissolve tricalcium phosphate. All bacterial isolates were able to produce hydrogen cyanide. In assessing the ability of isolated endophytic bacteria to produce protease enzyme, clear zone formation was observed only around the colonies of S1, S4, B9, B12, B3, B11, R7, p < sub>6 and p < sub>4. It is suggested that the effects of superior isolates on growth and yield of medicinal plants used in this study should be investigated in greenhouse and field conditions before any recommendation.