Rhizo-inoculation of phosphate solubilizing bacteria strains to improve rice (Oryza sativa L. var. FARO 44) growth under ferruginous ultisol conditions.
Abstract Background The research investigated the possibility of phosphate solubilizing bacteria (PSB) with plant growth-promoting (PGP) capabilities to improve growth properties of rice plant under ferruginous ultisol (FU) condition through rhizo-inoculation strategy. The PSB with PGP properties used in this research were Bacillus cereus strain GGBSU-1, Proteus mirabilis strain TL14-1 and Klebsiella variicola strain AUH-KAM-9 that were previously isolated and characterized following the 16S rRNA gene sequencing. The rice seeds were sown in a composite FU soil sample and a humus soil (control) and then rhizo-inoculated along the root region of the growing rice seedling at 16 days after sowing. The rice plant was studied for differences in morphological, physiological and biomass parameters for 16 weeks after rhizo-inoculation. Results The composite FU soil used in the study had high pH, low bioavailable phosphorus, low water holding capacity and high iron levels which has led to a low growth properties of rice seeds sown in FU soil without rhizo-inoculation. After rhizo-inoculation, a significant increase in morphological, biomass and physiological parameters were observed in the rice plant grown in the FU soil as against the control and the rice plant in FU soil without inoculation except for terpenoid which is usually known to signify biotic stress and as part of plant defense mechanism. Generally, Bacillus cereus strain GGBSU-1 showed higher improvement compared to other PSBs used in the present study. This is due to a more improved growth properties observed. Conclusion Rhizo-inoculation of rice seedling with Bacillus cereus strain GGBSU-1, Proteus mirabilis strain TL14-1 and Klebsiella variicola strain AUH-KAM-9 under FU soil condition significantly improved growth properties of the rice plant. This suggest the ability of PSB to solubilize and mineralize soil phosphate and improve its availability for plant use in phosphate stressed soil, thereby improving plant growth properties.