Seed bio-priming with phosphate-solubilizing bacteria strains to improve rice (Oryza sativa L. var. FARO 44) growth under ferruginous ultisol conditions

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 bio-priming 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. Biosafety analysis of the PSB isolates was conducted using blood agar. The rice seeds were then bio-primed with the PSBs at 3, 12 and 24 hours priming durations and then sown in a composite FU soil sample. Differences in germination bioassay involving SEM, morphology, physiology and biomass parameters were investigated for 15 weeks after bio-priming. 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 without bio-priming in FU soil. Germination parameters was better in seeds bio-primed with the PSBs, especially at 12h priming duration as against seeds without priming. SEM showed more bacterial colonization in the PSB bio-primed seeds. Seed bio-priming of rice seed with Bacillus cereus strain GGBSU-1, Proteus mirabilis strain TL14-1 and Klebsiella variicola strain AUH-KAM-9 under FU soil condition significantly improved seed microbiome, rhizocolonization and soil nutrient properties, thereby enhancing growth properties of the rice plant. This suggest the ability of PSB to solubilize and mineralize soil phosphate and improve its availability and soil property for optimum plant usage in phosphate stressed and iron toxic soils.