Isolation, identification, and functional characterization of plant growth-promoting bacteria from peanut seeds

Abstract:

[Background] The application of plant growth-promoting bacteria is an important measure for the sustainable development of agriculture. The seed-associated bacteria can interact with plants in the early lifecycle, being of great significance to plant growth. [Objective] To screen out the seed-associated bacterial strains with the function of promoting plant growth and inhibiting plant pathogens, to underpin the application of the strains in agricultural production. [Methods] The plant growth-promoting bacteria were isolated from the surface and the inside of peanut seeds. The roles of the isolates in promoting plant growth (nitrogen fixation, phosphorus solubilization, and IAA and siderophore production) and inhibiting the growth of plant pathogens were examined. The 16S rRNA gene sequencing was employed to determine the taxonomic status of the isolates. The biofilm formation and rhizosphere colonization tests were carried out to measure the viability of the strains in plant rhizosphere. Finally, pot experiments were conducted to examine the effects of the plant-growth promoting bacteria on the seed germination and seedling growth of peanut. [Results] A total of 41 plant-growth promoting bacterial strains were isolated from peanut seeds. All of the strains were capable of producing IAA, and 35, 2, and 14 strains showed the abilities of fixing nitrogen, secreting siderophores, and inhibiting plant pathogens, respectively. The representative strains (the surface/inside of peanut seed and the inside of peanut radicle), PS3, PE5, and PR5, were chosen according to the results of phylogenetic analysis and identified as Bacillus sp. The three strains formed folded biofilms on the surface of MSgg liquid medium and colonized the surface of peanut roots. They increased the seed germination rate and promoted the seedling growth of peanut. Specially, PS3, PE5, and PR5 increased the seed germination rate from 14.17% to 38.33%, 30.83%, and 39.17%, respectively, on day 2. Compared with the control, PS5 increased the seedling height, root length, fresh weight, and dry weight by 21.82%, 22.20%, 37.11%, and 35.64%, respectively; PE5 increased them by 17.45%, 18.93%, 26.10%, and 21.18%, respectively; PR5 increased them by 23.11%, 23.92%, 38.66%, and 37.47%, respectively. [Conclusion] The bacterial strains with high efficiency in promoting plant growth were isolated from peanut seeds, and significantly promoted seed germination and seedling growth. The strains provide potential resources for agricultural production, with excellent application potential.