Abstract: Banana fusarium wilt was caused by Fusarium oxysporum f. sp. cubense race 4（Foc 4）. The changes of pathogenic activity of Foc 4 crude toxin after the treatments of autoclave，different pH values，ultraviolet irradiation and methanol precipitation were determined so as to understand the basic physicochemical properties of the toxin. The results showed that the toxin had a strong thermal stability，and still had a strong pathogenic activity after autoclave for 20 min；The pathogenic activity of the toxin would be reduced under both acidic（pH 3–6）and alkaline（pH 8–10）conditions；The supernatant rather than precipitation had the pathogenic activity after methanol precipitation treatment；The ultraviolet radiation could reduce the toxicity of the toxin. The above mentioned findings suggested that the toxin belongs to a small molecule，non-protein compound with higher polarity. Furthermore，effects of the toxin on seed germination and plantule growth of different plant species were determined so as to understand the host specificity of the toxin，and the results indicated that the toxin had different inhibitions on the seed germination and plantule growth of different plant species，indicating that the toxin was a non-host specific toxin.

Key words: Fusarium oxysporum f. sp. cubense, toxin, physicochemical property, pathogenic activity, host specificity