Screening and identification of salt-tolerant and growth-promoting microbial strains in the rhizosphere and their effect on the salt tolerance of Bermuda grass

Salt stress severely inhibits plant growth, but plant rhizosphere growth-promoting microorganisms can tightly interact with plants and alleviate such stress, improving resistance to salt stress and stimulating plant growth. In this study, microorganisms were screened on saline medium by the plate scribing method. Salt-tolerant and growth-promoting strains were isolated from the rhizosphere soil of Bermuda grass (Cynodon dactylon), and their biological and molecular properties were characterized. In total, 27 strains (12 bacterial strains and 15 fungal strains) were isolated from Bermuda grass rhizosphere soil samples and subjected to pure culture, including one strain of an indole-3-acetic acid (IAA) high-yielding fungus (Z7), 10 strains of IAA-producing bacteria or fungal (X1, X2, X8, X10, X11, X12, Z2, Z3, Z9, Z13), and five strains of phosphorus-solubilizing bacteria or fungal (X1, Z2, Z4, Z5, Z14). Six salt-tolerant and growth-promoting strains (X8, X11, X12, Z3, Z7, Z9) were finally screened via exogenous addition experiments to confirm their promoting effects on the growth and salt tolerance of Bermuda grass. Our results showed that strains X8, X11, X12, Z3, and Z7 could stimulate the growth of Bermuda grass in both salt stress and non-salt stress conditions. Particularly, strain Z9 had no evident growth-promoting effect in non-salt stress conditions. However, under salt stress, it could increase the root length and underground fresh weight of Bermuda grass by 27.5% and 85.2%, respectively. In summary, all six candidate strains had better effects on root length and underground fresh weight under salt stress, with growth-promoting rates ranging from 3.3% to 32.0% and 29.0% to 96.7%, respectively. In this study, six candidate rhizosphere growth-promoting microorganisms were screened for Bermuda grass subjected to salt stress.