Improving growth and yield of maize through bioinoculants carrying auxin production and phosphate solubilizing activity

In this study, effect of three rhizobacteria, Bacillus megaterium (K2), Bacillus subtilis (K4) and Bacillus sp. Cp-h6 (K6) varying in P solubilization, ACC deaminase activity and auxin production were evaluated for promotion of shoot and root growth, yield and P uptake by maize plant under different P sources (control, rock phosphate and DAP). All the three strains used in this study had different phosphate solubilization potential but as phosphate solubilization potential increased from K2 to K6 (from 180 to 698 mug mL-1), the auxin production potential decreased accordingly (from 48.1 to 8.2 mug mL-1). Bacillus sp. Cp-h6 showed more enhancement effect on the tested parameters compared to Bacillus megaterium and Bacillus subtilis with all three P sources. Furthermore, in uninoculated plants, DAP was more effective than rock phosphate, but DAP response (percent increase) was least under inoculation. Maximum increase was recorded in plant parameters where rock phosphate and bioinoculants were applied together. In pot study, shoot length of maize plants increased from 89.8 to 125 cm with DAP (39% increase) while with rock phosphate, it increased from 49 to 97.7 cm (99% increase) through inoculation. Likewise, percent increase over uninoculated control caused by the bacterial inoculation in shoot dry matter was 77 and 134 in pot study while 26 and 65 under field conditions with DAP and rock phosphate, respectively. Similarly, substantial increment in the root dry matter yield, root length, cob weight, kernel yield, P uptake in stover and P uptake in kernel were recorded with inoculation of rhizobacterial strains. In conclusion, rock phosphate could be effectively used as P source in the presence of these bioinoculants, particularly Bacillus sp. Cp-h6. The bioinoculant could be used for developing biofertilizer for field application to improve yield and quality of maize kernels.