Effect of Plant Growth Promoting Rhizobacteria on Morphological Traits and Essential oil Content of Moldavian Dragonhead (Dracocephalum moldavica L.)

Dragonhead or Moldavian dragonhead (Dracocephalum moldavica L.), which belong to Lamiaceae family is an annual medicinal herbaceous and aromatic plant that its essential oil is used widely in medicine, food, cosmetic and health industries. Due to the importance and role of medicinal plants in various industries, there is an increasing demand for herbal medicines. The indiscriminate use of chemical fertilizers has increased crop production, but has also harmed ecosystems. Some studies show that the use of some microbial species that are collectively designated as plant growth promoting rhizobacteria (PGPR) can improve yield and quality of medicinal plants. Given the importance of environmental health and food safety, this study aimed to investigate the effect of PGPR on morphological traits and essential oil content of Moldavian dragonhead.
This experiment was conducted in randomized complete block design with eight treatments and three replications at research station of faculty of agriculture, Shahrekord university. No bacterial inoculation was used as control and seeds inoculated with Rhodococcus sp., Corynebacterium sp., Mycobacterium sp., Bacillus sp., Azotobacter sp., Pseudomonas putida, Pseudomonas fluorescens were considered as bacterial treatments.
The results showed that all bacterial treatments had a significant effect on plant height, number of branches, number of flowering shoot, leaf dry weight, shoot dry weight, biological yield, crop growth rate (CGR), leaf area (LA), chlorophyll a, chlorophyll b, essential oil content and yield. Mycobacterium sp. treatment had the most effect on plant height, number of branches, leaf and shoot dry weight, number of flowering shoot, biomass and chlorophyll b. Bacillus sp. treatment had the most effect on leaf dry weight, number of flowering shoot, leaf area and essential oil content and yield. The highest crop growth rate and chlorophyll a were observed in Rhodococcus sp.treatment.
In general, the Bacillus sp., Mycobacteriumsp., Rhodococcus sp., andPseudomonas putida treatments had the most influence on Moldavian dragonhead. Since the purpose of medicinal production is obtaining the highest content of essential oil and biomass yield, based on these results, the use of Bacillus sp., and Mycobacterium sp., bacterial inoculation treatments, as biopriming, can be recommended for increasing biomass and essential oil content in Moldavian dragonhead.