Isolation and identification of drought-tolerant plant growth-promoting rhizobacteria from tall fescue and their growth-promoting effects

Rhizobacteria with drought tolerance and growth-promoting effects were isolated from the rhizosphere soil of drought-treated tall fescue (Festuca arundinacea), and their growth-promoting effects were investigated in combination with plant inoculation experiments to provide high-quality bacterial resources and theoretical basis for the enhancement of drought tolerance of turfgrass. A total of 24 strains of bacteria were isolated and purified from the rhizosphere using the plate dilution method, identified by combining morphological characteristics and 16S rRNA sequence analysis and evaluated for their growth-promoting effects and polyethylene glycol-6000 (PEG-6000) tolerance; two strains were screened for their ability to dissolve phosphorus and potassium, and good PEG-6000 resistance. On this basis, two plant growth-promoting rhizobacteria, Klebsiella indica and Shigella flexneri, with both phosphorus solubilizing and potassium solubilizing abilities as well as good PEG-6000 tolerance were screened and inoculated in pots. The results of the inoculation demonstrated that these two biotrophic bacteria were able to promote the growth of tall fescue seedlings under drought stress, and the 1:1 mixture of the two strains had a better growth-promoting effect; meanwhile, the inoculation treatment was able to reduce the water loss rate of isolated leaves of tall fescue cultivar ‘Acending Star’. In addition, strain K. indica had the ability to increase the proline content of tall fescue seedlings under drought stress, while strain S. flexneri had the ability to increase the germination rate of tall fescue seeds and was able to reduce the relative exudation rate of electrolytes in tall fescue. The results indicated that K. indica and S. flexneri had better drought tolerance and provided strain resources for further application of the inter-root biotrophic bacteria in the development of efficient microbial fertilizers for turfgrass.