Effects of plant growth promoting rhizobactria and chemical fertilizer on growth, yield, flowering, physiological properties, and total phenolic content of Calendula officinalis L.

In order to investigate the effects of Plant Growth Promothing Rhizobacteria (PGPR) on growth, yield, flowering and biochemical content of marigold (Calendula officinalis L.), an experiment was carried out in a randomized complete block design with five treatments and four replications during the 2015-2016 in the Faculty of Agriculture of Shahid Chamran University of Ahvaz. The treatments included Entrobacter closea R13, Entrobacter closea R33, Pseudomonas sp., chemical fertilizers (NPK), and control (no fertilizer). The results of the experiment showed that the highest flower number per square meter, leaf number, stem branches, receptacle diameter, and capitol diameter were observed in E. closea R13, while the highest capitol fresh and dry weight was found in E. closea R33. Moreover, the most leaf phosphorus and nitrogen content, and leaf chlorophyll and carotenoids content were observed in the plots incubated with E. closea R13. The highest and lowest total phenolic content was found in the Entrobacter treatment and control, respectively. Mean comparison of treatment effects showed that the effects of E.closea R33 were similar to E. closea R13 in most parameters and there was no significant difference between them. According to the positive and additive effects of PGPR on calendula plants, the PGPR could be recommended as an alternative to chemical fertilizers to reduce the consumption of chemical fertilizers and guaranty the production of medicinal plants, free of chemicals.