effects of drought stress and bio-fertilizers inoculation on growth, essential oil yield and constituents of thyme (thymus vulgaris l.)

thyme (thymus vulgaris l.) is perennial aromatic shrub belonging to the mint family which has anti-spasmodic, antiseptic, carminative, anti-cough, sputum and antioxidant properties. in order to study the effects of drought stress and bio-fertilizer on plant growth, essential oil yield and constituents of thyme plant, an experiment was conducted in a split plot based on randomized complete block design with two replications, at the research farm of zabol university, during growing season of 2012 and 2013. main plots consisted of irrigation with 30, 50, 70 and 90% field capacity and subplots including plant inoculation with nitroxin, bio-phosphorus and mycorrhiza. plant traits such as plant height, fresh and dry weight of herb per plant, essential oil percentage, yield and constituents of thyme were measured. effects of drought stress, bio-fertilizer and their interactions on all studied traits were significant at the 1% probability level. the highest plant height (35.09 cm), fresh and dry weight of herb per plant (103.52 and 43,27 g.plant-1, respectively) and essential oil yield (0.350 ml.plant-1) belong to treatment of irrigation with 90% field capacity and nitroxin bio-fertilizer. the maximum essential oil percentage with 0.413% was obtained by irrigation with 70% field capacity and nitroxin bio-fertilizer. fresh weight of herb per plant was the most crucial component in determining essential oil yield in thyme. plants irrigated with 70% filed capacity gave the highest relative percentage of thymol, which reached 71.32, 50.68 and 47.71% in nitroxin, biophosphorus and mycorrhiza biofertilizer, respectively. this effect was accompanied with decrease in -cymene content. inoculation with nitroxin bio-fertilizer as compared to other fertilizers could further amend drought stress and improved the plant growth, essential oil percentage and yield and phenolic compound thymol of thyme. thus, it appears that in order to achieve sustainable agriculture instead of chemical fertilizers is recommended.