Abstract: Two plant growth-promoting bacteria, strains Rs-5 and Rs-198, isolated from salt-stressed cotton rhizosphere, could improve germination rate of cottonseed under salt stress. The ability of solubilizing tricalcium phosphate and secreting IAA (indo-3-acetic acid) of strains Rs-5 and Rs-198 were tested.Cotton seeds germination was tested by pot experiment. Spectrophotometrically with Mo-Sb-VC and Salkowski methods were used to determine content of solubilizing tricalcium phosphate and IAA.The two bacteria strains were characterized as Rs-5 Klebsiella.sp and Rs-198 Pseudomonas.sp. The germination rates was 26.3 % and 34.4 % more than control. During seven days fementation, the soluble phosphate contents solubilized by the strains Rs-5, Rs-198 in fementation broth reached to 73.38 mg•L-1 after incubating 24 hours and 82.41 mg•L-1 after 48 hour, respectively. The pH value in fermentation broth of the two strain decreased from 7.48 to 5.22 and 4.54, respectively. Contents of IAA secreted by Rs-5 and Rs-198 in cultures were accumulated following the incubation time. The contents of IAA were accumulated to 7.09 mg•L-1mg•L-1 and 10.77 mg•L-1 each at 96 hours fermentation. Phosphate solubilizing and IAA secretion might be the main reason for promoting cotton germination under salt stress.

Key words: cotton, relieving-salt-stress and plant-growth-promoting, solubilizing tricalcium phosphate, IAA , bacteria