influence of seed inoculation with promoting rhizobacteria on the germination and growth traits of astragalus cyclophyllon beck under drought stress

the plant growth-promoting rhizobacteria (pgpr) are one of the famous sources when applying drought stress management in rangeland plants. this research was conducted to investigate the effect of pgprs on the germination and growth of astragalus cyclophyllon beck under drought stress. a factorial experiment in a completely randomized design with three replications, was conducted in the seed laboratory. the effects of the main factors of pgpr inoculation as well as control and drought stress at four levels and their interactions on weight, length, and germination indices were investigated. bacillus cereus had the highest effect on increasing shoot, seedling dry weight, and vigour indices. pseudomonas aeruginosa had the highest effect on promoting radicle length. additionally, results revealed that -0.8 mpa drought stress had a significant effect on radicle and shoot fresh weight, shoot and seedling length, germination percentage, germination rate and mean daily germination as compared to 0.0, -0.2 and -0.4 mpa indicating a. cyclophyllon is a drought stress resistance species. b. cereus at the control level of drought stress significantly increased shoot and seedling dry weight and vigour indices, whilst, p. aeruginosa at the drought stress level of -0.8 mpa significantly increased shoot lengths compared to control. in general, b. cereus significantly increased biomass by increasing shoot and seedling dry weight but p. aeruginosa affected elongation growth of the plant by increasing radicle and shoot lengths of a. cyclophyllon. suitable pgpr as biotic elicitors can enhance the growth of the rangeland plants.