Abstract: The aim of this study is to isolate and screen plant pathogenic strains with strong herbicidal activity, providing new bacterial resources for the development of microbial herbicides. The naturally infected plants of Sorghum halepense were collected, and the strains were isolated and purified by tissue and single spore isolation. The strain BS-1 was identified as Fusarium oxysporum by colony morphology observation and ITS identification. The effect of spore suspension with concentration of 1.0×10⁵-1.0×10⁷ spores/mL on the germination rate of S. halepense seeds and the pathogenic effect of young plants were measured by petri dish filter paper method and live pot method. The results showed that the germination rate of S. halepense seeds after treatment with different concentration of spore suspension was lower than 33%, and strain BS-1 had a significant inhibitory effect on the germination of S. halepense seeds. The inhibitory effect on the radicle was greater than that on the germ, and it also had different degrees of pathogenicity on the seedings. The results of live pot experiment showed that different concentration of strain BS-1 fermentation liquid also had different degree of pathogenic effect on the young plants of S. halepense. At 14 days, the incidence rate of S. halepense plants was more than 40.07%, the disease index was more than 33.72%, and the inhibition rate of fresh weight was more than 46.54%. When the concentration was 1.0×10⁷ spores/mL, the seeds could not germinate. At 14 days, the pathogenic rate of the seedlings reached 98.12 %, the disease index was 88.72 %, and the fresh weight inhibition rate was 89.23 %, which had strong pathogenicity to the seedlings. Finally, the pathogenicity of strain BS-1 against four associated weeds of S. halepense and the safety of five main crops were evaluated at this treatment concentration. The results showed that the strain also exhibited varying degrees of pathogenicity against weeds such as Echinochloa crus-galli, Digitaria sanguinalis, Eleusine indica, and Cenchrus echinatus. Especially, it has a significant pathogenic effect on Eleusine indica and Echinochloa crus-galli, with pathogenic rates of 88.52% and 87.77%, disease index of 79.42% and 78.69%, and fresh weight inhibition rates of 84.48% and 81.11%, respectively. But it has high safety for the main crops Zea mays, Oryza sativai, Brassica rapa var. chinensis, Brassica rapa var. glabra, and Coriandrum sativum. Therefore, the strain BS-1 has the potential to be developed as a microbial herbicid, and the research results also provide strain resources and experimental basis for field biological control of S. halepense.

Key words: Sorghum halepense, Fusarium, pathogenicity, security, biological control