Bio-priming of soybean with Bradyrhizobium japonicum and Bacillus megaterium

Seed bio-priming with plant growth-promoting rhizobacteria (PGPR) can enhance seed germination and improve seedling growth. Laboratory experiments were conducted to evaluate the effects of single and co-inoculation with Bradyrhizobium japonicum (strains from commercial inoculant) and Bacillus megaterium (newly isolated strains from soil) on seed germination and initial seedling growth of two soybean cultivars. The treated seeds were subjected to a germination test, a cold test and an accelerated aging test. Plant growth-promoting (PGP) characterization of the selected B. megaterium strains revealed the production of indole-3-acetic acid (IAA) and siderophores, nitrogen fixation, and phosphate solubilization/mineralization. Bacterial treatments remarkably improved seed quality and viability in all the tests, with the greatest improvement in cold-treated seeds, followed by aged and normal seeds. On average, single inoculation with B. megaterium had the highest effect on germination (4.0% and 4.1%) and seedling vigor index (12.5% and 32.4%) in normal and aged seeds. The highest increase in germination (7.8%) was detected in B. japonicum, while co-inoculation had the best effect on seedling vigor index (48.5%) of the cold-treated seeds. The results confirmed that indigenous strains of B. megaterium from soil could be used in soybean production both as single and co-inoculant, especially under adverse conditions.