Phosphate solubilizers as antagonists for bacterial leaf blight with improved rice growth in phosphorus deficit soil

Multifaceted phosphate solubilizing bacteria (PSB) promote growth of plants by acting both as biofertilizer and biopesticide. The present study aimed to use native beneficial rhizobacteria to suppress rice Bacterial Leaf Blight (BLB) pathogen as well as to combat the plant in P deficiency without reduction in crop yield. In present investigation, of 50 PSB isolated from rice rhizosphere, three bacterial strains inhibited the BLB pathogen (18-25 mm), solubilized phosphorus (up to 197 mu g mL(-1)) produced IAA (1.7-14 mu g mL(-1)). Gluconic acid produced by phosphate solubilizing antagonistic bacteria and molecular confirmation through amplification of glucose dehydrogenase genes (gcd) showed that gluconic acid may have dual role in P solubilization as well as BLB suppression. Plate germination assay showed that increase in vigor index (27%), root diameter (29%), root length volume(-1) (57%) and root projection area (43%) were observed in inoculated seedlings as compared to uninoculated control. Plant inoculation studies under net house conditions showed BLB disease suppression (up to 56%) along with increase in plant P contents (up to 0.47% in straw and 1.26% in seed) in treatments inoculated with Pseudomonas spp. MR11, MR34 and Bacillus sp. MR42. Increase in the activity of defense related enzymes Phenylalanine ammonia lyase (PAL: 5.165 activity as mu mole cinnamic acid g(-1). f. wt.), Catalase (CAT: 2.88 activity g(-1). f. wt.), Peroxidase (POD: 2.4 activity g(-1). f. wt.), beta, 1-3 glucanase (283 activity g(-1). f. wt.) and Polyphenol oxidase (PPO: 65 activity g(-1). f. wt.) were observed in response to inoculation of P-solubilizing antagonistic bacteria. BOX PCR finger printing and viable cell count coupled with Fluorescent in situ hybridization showed the competence and survival of inoculated bacteria in rhizosphere and phyllosphere. The findings of the current research work strongly encouraged the use of PSB strains for BLB suppression in phosphorus deficient soils.