Abstract: ObjectiveThe research evaluated toxin production cultural conditions for Alternaria alternata strain LGB100401 and herbicidal activity of the toxin,in order to provide theoretical basis for biological control of Chromolaena odorata.MethodA.alternata strain LGB100401 isolated from infected C.odorata in field in Hainan was taken as material.The bioassay-guided ethyl acetate extract and silica gel column chromatographic separation were used to isolate,purify the toxin and research the toxin production conditions.Sensitivity of 38 species of plants to the toxin was tested using detached leaf puncture inoculation method.ResultResults showed that LGB100401 could produce toxins which led to necrosis of C.odorata leaf.The optimal cultural conditions for producing toxin were temperature 25 ℃,pH 4-6,cultured period 15 d under alternation of light and dark.The toxin had selective toxicity towards the 38 species of plants.Sixteen species were not sensitive (NS) to the toxin,four species were slightly sensitive (LS),eight species were sensitive (MS) and four species were very sensitive(SS).The four species which were very sensitive were C.odorata,Digitaria sanguinalis,Tridax procumbent and Malvastrum coromandelianum.Among the six tested crops,only rice was sensitive(MS) to the toxin,the rest five crops were not sensitive or only showed slight symptom.ConclusionAlternaria alternata toxin from C.odorata has strong inhibitory effect on C.odorata.It may be useful for biological control of C.odorata.