Isolation and characterization of rhizobacteria and their effects on root extracts of Valeriana officinalis.

Plant growth promoting rhizobacteria (PGPR) are a group of microorganisms which can enhance growth parameters of host plants and can be used as biofertilizers. Valerian (Valeriana officinalis) is a perennial herb which is used as a medicinal plant. In the current study 40 colonies of bacteria were isolated from the rhizosphere of valerian by growing in various enriched and selective media including S1 and King B, crystal violet agar and methyl red agar. Furthermore, the ability of bacteria to produce siderophore, indoleacetic acid (IAA), hydrogen cyanide (HCN), lipase and protease were tested in vitro. Identification of isolates was performed by using Bergey’s manual of systematic bacteriology. Additionally, the effects of seven isolated bacteria (belong to Pseudomonas genus) that showed a high potential of siderophore, IAA, HCN, lipase and protease production on the quantity of root extracts were investigated under greenhouse condition. Results showed that the population of Pseudomonas was the highest in comparison to other genera in the rhizosphere of plant. Isolated bacteria could mostly produce siderophore, lipase, HCN and protease. Two isolates (belong to Pseudomonas genus) significantly increased the amount of valerenic acid in the root extract. The results revealed that PGPR increased shoot length and could also enhance quantity of root extract