Abstract:Fusarium wilt of watermelon caused by Fusarium oxysporum f. sp. niveum is a destructive soilborne disease in watermelon production. However, no effective method has been developed to control the disease. For exploration of a biological control method against the wilt, antagonistic bacteria were isolated, screened and used to make biological organic fertilizers, which were further tested for their diseasecontrol effectiveness by a greenhouse pot experiment. The antagonism related β-1,3-1,4-glucanase was also detected by a molecular biological procedure. A total of 172 strains were isolated from rhizosphere soils of different fields. Among the strains, 13 strains had the inhibition rates more than 60% in antagonistic plates and two strains Cy5 and CR38 with the highest inhibition rates were used to make biological organic fertilizers, i.e. BIO5 and BIO38, respectively, for greenhouse pot experiments. The results showed that BIO5 microbial composition in performed better than BIO38 in control of the disease and promotion of the growth of watermelon. The relative control rates of BIO5 and BIO38 were 75% and 25%, respectively, as compared with the control. The averages of height, fresh weight and dry weight of the plants in the treatment of BIO5 were increased by 64.8%, 63.0% and 50%, respectively, in comparison with the control. BIO5 also significantly improved rhizosphere soil of watermelon. BIO5 increased the numbers of bacteria and bacillus subtilis in rhizosphere soil of watermelon by 48.5% and 61.1%, respectively, and decreased the numbers of fungi and F. oxysporum by 52.1% and 70.2% respectively, as compared with the control. Molecular analysis showed that strain Cy5 belonged to Paenibacillus jamilae and contained β-1,3-1,4-glucanase similar to that of P. polymyxa. We concluded that the antagonistenhanced biological organic fertilizer had control potential against Fusarium wilt of watermelon.