Integrated effect of plant growth-promoting rhizobacteria and phosphate-solubilizing microorganisms on growth of wheat (Triticum aestivum L.) under rainfed condition

Abstract Background Biofertilizers are now considered to be the only alternative of chemical fertilizers which apart from their soaring cost are enhancing in pollution hazards of our environment. Increasing and extending the role of biofertilizers would reduce the need for chemical fertilizers and consequently decrease adverse environmental effects. Results After morphological and physiological characterization, 7 isolates out of 63 were selected as PGPR and seven as phosphate-solubilizing microbes (PSM). All seven PGPR exhibited indole acidic acid (IAA) production, whereas five isolates produced gibberellic acid (GA) ranging from 5.5 to 30.6 and 10.0 to 14.8 mg L−1, respectively, isolate WPR-51 have highest concentration of IAA and GA. Two isolates (WM-1 and WM-2) did not showed GA production in culture solution. Phosphate solubilizing index (SI) of seven isolates was recorded for 6 days in an incubation study. The P solubilization was also quantified through spectrophotometry and was found to range from 25 to 130.1 µg mL−1. These two isolates were further studied for their organic acid production (oxalic acid, citric acid and gluconic acids) through HPLC. The isolates PSM 202 showed higher acid production as compared to PSM-305. After biochemical screening, three PGPR (WRP-32, WRP-42 and WRP-51) and one PSM-202 were used in eight different combinations to test their effect on seed germination, seed vigor and root length in a 6-day Petri plates study. After laboratory study, a pot study was carried out, to verify the results of incubational experiment. Data were collected on root shoot length and root shoot biomass after 8 weeks of transplantation. Statistical analysis showed that among eight treatments, mixture or co-inoculation treatment (T8) (WPR-42 + WPR-51 + WPR-32 + PSM) ranked as first followed by treatment (T5) (WPR-51 + PSM) that significantly increased root shoot length and biomass as compared to un-inoculated treatment. Three PGPR isolates (WPR-42, WPR-51, WM-1) were also tested for their antifungal activity on seed germination of two wheat varieties and confirmed their antifungal activity against Rhizoctonia solani. The isolate WPR-51 and mixture of 3 isolates completely neutralized the harmful effects of Rhizoctonia solani as 100% of the seeds of both varieties germinated in these treatments. Conclusion The integrated effect of co-inoculation treatment of selected PGPRs (WRP-32, WRP-42 and WRP-51) and PSM-202 were found better in promoting crop growth and controlling disease as compared to all others treatments