Isolation and Characterization of Indigenous Plant Growth-Promoting Rhizobacteria (PGPR) from Cardamom Rhizosphere

The present study was conducted to explore the native plant growth-promoting (PGP) bacteria from cardamom rhizosphere in few districts of Kerala and Tamilnadu under cardamom cultivation. The isolates obtained were screened for their PGP characteristics and their beneficial effect on cardamom was evaluated. Of the total 88 isolates, ten were screened as promising based on their performance in growth promoting attributes such as production of indole acetic acid, gibberellic acid, siderophore, hydrogen cyanide, heavy metal tolerance and antibiotic resistance. Diazotrophy of the screened isolates were tested by nitrogenase assay and evaluated using the diversity of nif genes. Genetic analysis was carried out to assess the phylogenetic relationship using 16S rRNA sequencing. The phylogenetic analysis exhibited clear clustering of isolates into three phyla namely Firmicutes, Actinobacteria and γ-proteobacteria. Majority of the isolates were grouped into Bacillus and Pseudomonas at genus level. Three different plant inoculation study at nursery and field level, viz., Bacillus subtilis TAUC1, Bacillus subtilis TAUC2 and Pseudomonas putida TAUC10. The combined inoculation of bioinoculants were superior over individual inoculation with respect to growth, soil and plant nutrient content, biochemical constituents, rhizosphere population, soil enzyme activities and yield. Hence the present study reveals the potential effect of PGPR for bioinoculant production for enhancing growth and development of cardamom under field conditions.