Isolation and Characterization of Three Plant Growth-Promoting Rhizobacteria for Growth Enhancement of Rice Seedling

Biofertilizers are currently considered the only alternative of chemical fertilizers. In addition, improving the effect of biofertilizers can make chemical fertilizers less demanded, thereby leading to the reduction of adverse environmental effects. In the present study, three rice rhizosphere bacteria (Bacillus megaterium DD-2, Bacillus aryabhattai DD-3 and Bacillus subtilis DD-4) were isolated and then identified from the soil of a farm in Northeast China. As revealed from the results, all isolates exhibited the ability to dissolve potassium and phosphorus. To be specific, DD-4 was capable of dissolving potassium to the greatest extent (1.37 mg/L), DD-2 could maximally dissolve inorganic phosphorus (288.33 mg/L) and DD-3 exhibited the maximum solubility of organic phosphorus (31.58 mg/L). All isolates were capable of synthesizing Indole-3-acetic acid (IAA) (55.66 ~ 75.89 mg/L), Gibberellic acid (GA) (16.33 ~ 23.58 mg/L) and siderophores (38.77 ~ 52.88%). As suggested from the results of the pot experiment, the isolates were capable of promoting the shoot and underground part of rice seedlings. With the increase in the concentration of isolates and the time of addition, the overall effect of the isolates to boost rice seedling growth first increased and then leveled off. The mentioned isolates were observed to exhibit great potential for being biologically applied. However, the impact of isolates on rice required more specific assessments under biotic and abiotic stress before being recommended as biofertilizers.