Abstract: Rhizosphere phosphate solubilizing bacteria can improve utilization of phosphorus in soil and promote plant growth. In this study， the bacteria， which could solubilize phosphate efficiently， were identified by selective medium and their effects on the root growth of watermelon seedling were investigated in a pot experiment. The results showed that 7 strains with the capability of phosphate\|dissolving were identified， HYL01 strain was the strongest than other strains in the capacity of phosphate solubilization， and was classified as Pantoea ananatis. It could dissolve Ca3（PO4）3 with a rate of 14026 mg·L-1， and the correlation coefficient was -0743 between the solubilizing capacity of phosphate and pH value. Compared with the control， the total root length， root surface area， root volume and specific root length of watermelon seedlings were increased by 4438%， 758%， 6365% and 1632% by HYL01 strain. The proportion of fibrous roots， which had a diameter in the range of 0-05 mm， was increased significantly in watermelon seedlings. Therefore， HYL01 strain had the capacity to dissolve inorganic phosphorus efficiently and could promote root growth of watermelon seedlings. It is an excellent candidate for compound microbial fertilizer.

Key words: phosphorus solubilizing bacteria, watermelon, root, promoting effect