Abstract: The objective is to select a natural antagonistic bacterium efficiently controlling Fusarium oxysporum f. sp. niveum that is the pathogenic bacterium of the fusarium wilt of watermelon. Using the method of gradient dilution to isolate actinomycetes from rhizosphere soil of continuous cropping pepper,it was purified and the plate confrontation method was applied to select an antagonistic strain. Then the method of basin nursery substrates mixed with bacteria was for inoculation,a potted plant disease-resistant experiment was carried out,and the strains with the optimal antagonistic effects were identified. The results showed that 10 strains of actinomycetes with the antagonistic effects to fusarium wilt of watermelon were isolated from the growing pepper rhizosphere soil,and 3 of them（F22,F23 and F32）presented the significantly antagonistic effects. After 96 hours the diameter of the inhibition zone was 1.70 cm,1.17 cm and 1.47 cm respectively. The result of the potted plant experiments demonstrated that the control effect of the antagonistic strain F32 to the fusarium wilt of watermelon reached maximum with 66.7% at 30 d,moreover,it also had a wide antibacterial spectrum. Based on the phenotypic characteristics,physiological-biochemical characteristics,and the results of 16S rDNA molecular analysis,the F32 was identified as Streptomyces sp.,and F32 presented solid control effects on the fusarium wilt of watermelon,thus it is biocontrol strain with potential application value.

Key words: fusarium wilt of watermelon, actinomycetes, antagonistic microorganism, biological control