Standardization of the biological hardening of tissue culture raised plants of Valeriana jatamansi Jones using plant growth promoting (PGP) bacteria

Valeriana jatamansi Jones is an important, high-value Himalayan medicinal species and is used in various herbal and pharmaceutical formulations. The purpose of this study is to examine the impact of plant growth-promoting (PGP) bacteria on the hardening and secondary metabolite production of V. jatamansi tissues grown in tissue culture. During the tests, various combinations were evaluated, including P. putida and B. subtilis (0.5 ml × 10^6 cells ml−1 each), and the B. subtilis (1.0 ml inoculated) plants had the highest survival percentage (90%). Likewise, the maximum plant height (29.60 cm) and leaf numbers (31.0 individuals) were recorded in P. putida (0.5 and 1.0 ml) inoculums, while the highest leaf area was found in B. subtilis (1.0 ml inoculums). Also, the maximum plant biomass (16.80 g) was found in mixed inocula. Results revealed a significant (p < 0.01) variation among analyzed parameters, and exhibited a higher amount of phenolics (2.78 mg GAE/g dw) in the root of B. subtilis (0.5 ml inoculums), tannins in leaf and root (5.42; 5.41 mg TAE/g dw respectively) of P. putida (0.5 ml inoculated plants). Antioxidant activities (IC 50), i.e., maximum DPPH activity (root 4.39; leaf 4.95 mg/g dw) in uninoculated plants, and NO· scavenging activity (root 7.28 mg/g dw) in P. putida (1.0 ml inoculums) was recorded. In addition, higher H2O2 concentration (36.90 µM/g fw), chlorophyll ‘a’, ‘a’ + ‘b’, and carotenoids content were obtained in uninoculated plants; however, maximum chlorophyll ‘b’ and carotenoids (2.99; 1.13 µg/g fw, respectively) were found in B. subtilis (0.5 ml) inoculated plants. According to the findings, PGP bacteria treatments that promote plant growth are effective in boosting survival rates and increasing biomass accumulation, and can be used to cultivate V. jatamansi.