The objective of this research was to find out the actinomycetes islates capable of inhibiting the growth and sporulation of Colletotrichum sp. fungus causing anthracnose disease on Soursop. There are 18 of 98 actinomycetes isolates in total presented antagonistic activity against Colletotrichum sp. and among these, 5 actinomycetes isolates HN-ĐT.1, LV-ĐT.1, LV-ĐT.3, AP-AG.1 and CT-HG.3 showed hightly antagonistic ability with the radiuses of inhibition zones reaches 10.4mm; 7.4mm; 7.8mm; 5.6mm and 6.9mm, respectively and antagonistic effect reaches 65.33%; 61.33%; 57.798%; 56.89% and 56.83%, respectively at 6 days after testing. On the other hand, the ability of inhibiting sporulation of Colletotrichum sp. by 5 actinomycetes isolates (HN-ĐT.1, LV-ĐT.1, LV-ĐT.3, AP-AG.1 and CT-HG.3) was conducted in Laboratory condition with 5 replications. The result showed that HN-ĐT.1 isolate had the highest inhibition effecicacy with the lowest log conidia concentration reaches 2.78 (spores/ml) at 9 days after testing.

Keywords: Actinomyces, anthracnose disease on Soursop, Colletotrichum sp., antagonistic activity, inhibiting sporulation.