Preliminary isolation and biochemical characterization of plant growth promoting rhizobacteria from Curcuma longa from the high-altitude region of Uttarakhand

Curcuma longa L. (common name: turmeric) is a medicinal herb with a rhizome and belongs to the Zingiberaceae family. The Indian subcontinent widely cultivates it, making it a significant commercial crop. Plant growth-promoting rhizobacteria (PGPR), which are found in the rhizosphere of plants, significantly contribute to plant growth. They aid in the mobilization and absorption of crucial nutrients like nitrogen, phosphorus, potassium, zinc, and others. They also contribute to the production of phytohormones by enhancing the microbial load, regulating both primary and secondary metabolite pathways, and promoting antibiosis. The current study isolated 20 rhizospheric bacterial isolates from 4 soil samples of C. longa from the high-altitude region of Uttarakhand. Out of the twenty isolates, eleven were Gram-positive, and the rest were Gram-negative. We further tested the isolates biochemically for the catalase test, citrate utilization test, oxidase test, and starch hydrolysis test. The analysis revealed that nine isolates tested positive for oxidase activity, seven for citrate activity, and eleven for starch hydrolysis activity, with isolate S4.4 exhibiting the highest activity in a clear zone of 2 cm. Additionally, all isolates tested positive for catalase activity. All the isolates were also tested for PGP activity based on phosphate solubilizing, ammonia production, and hydrogen cyanide tests. Two isolates demonstrated positive phosphate solubilizing activity, with isolate S3.2 displaying a maximum zone of 1.2 cm; 12 isolates yielded positive results for ammonia production, and the hydrogen cyanide test detected a positive result for isolate S2.2. From the results we can conclude that the bacterial isolates from the C. longa rhizosphere have some plant growth-promoting activity. Further studies are required to confirm their plant growth promotion competence. Exogenous application of beneficial microbes as a biofertilizer can be utilized for enhancing the yield, plant growth, and accumulation of curcumin in the rhizome of C. longa.