Isolation and Application of Rhizosphere Core Strains to Improve Salt Tolerance of Rice
[Objective]Rhizosphere beneficial microorganisms can enhance plant salt stress tolerance through multiple pathways,including re-establishing ion and osmotic homeostasis,preventing damage to plant cells,and resuming plant growth in saline soil.This study aimed to obtain plant growth-promoting rhizobacteria that can improve salt tolerance of rice and to explore its application effects.[Method]Two rice cultivars were used in this study,of which one is salt-tolerant cultivar Hunanxian and the other is salt-sensitive cultivar Nanjing 46.The physiological characteristics of rice seedlings were compared after planting in sterile and non-sterile saline soils.Then,the key rhizobacterial groups associated with salt tolerance,which were enriched in the rhizosphere of salt-tolerant rice cultivars,were identified by compositional differences and co-occurrence network analyses based on the 16S rRNA gene amplicon sequencing.Subsequently,the culturable strains of the key rhizobacterial groups were isolated through the high-throughput cultivation and identification method of rhizobacteria.Finally,pot experiments were conducted to evaluate the beneficial effects of the strains on enhancing the salt tolerance of salt-sensitive rice cultivar.[Result]The height of shoot and root length of salt-tolerant rice were significantly higher while the content of proline was significantly lower when cultivated in non-sterile soil than in sterile soil under salt stress.This indicates that the rhizosphere microbial community of salt-tolerant rice cultivars may play a crucial role in enhancing the salt tolerance of the host plant.Amplicon sequencing results demonstrated that the composition of the rhizosphere microbial communities of salt-tolerant and salt-sensitive rice cultivars was significantly different.The bacterial families of Flavobacteriaceae and Pseudomonadaceae were the key rhizobacterial groups that were both enriched in the rhizosphere of the salt-tolerant rice.Several bacterial strains affiliated with Flavobacteriaceae and Pseudomonadaceae were isolated,in which two strains of Pseudomonas punonensis P34 from Pseudomonadaceae and Chryseobacterium taeanense C18 from Flavobacteriaceae were screened to be the most efficient strains in improving the salt tolerance of rice by germination and hydroponics tests using salt-sensitive rice under salt stress.Finally,the efficient strains of C18 and P34 were applied as direct inoculants and seed-coating agents in pot experiments,and the results demonstrated that they were able to promote the growth of salt-sensitive rice under salt stress.[Conclusion]Two rhizobacterial strains of C18 and P34 showed great capacity to enhance the salt tolerance of rice and they could be developed as bacteriological agents for seed coating or microbial fertilizer for application in saline lands.
Saline soilSalt tolerance of riceRhizosphereCulturable strainSeed coating
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