The research was caried out from July to December 2022 in Laboratory of College of Agriculture, Can Tho University and the objective of this research was to investigate the actinomycetes able to antagonize with Neoscytalidium dimidiatum fungus causing stem canker disease on Dragon fruit. The antibacterial ability against N. dimidiatum fungus of the 16 actinomycetes isolates were examined with 5 replications in laboratory conditions. The results found that 4 actinomycetes isolates CT-LA2, CT-LA4, CT-LA5 and CT-LA9 have stronger antagonism with radius of inhibition zones reaches 10.8mm; 14.2mm; 10.6mm and 10.2mm and antagonistic efficacy 51.50%; 64.00% 52.50% and 50.59%, respectively 7 days after testing. On the other hand, the ability of inhibiting sporulation of N. dimidiatum by actinomycetes isolates (CT-LA2, CT-LA4, CT-LA5 and CT-LA9) was checked in laboratory condition with 5 replications. The result showed that CT-LA4 isolate has the highest inhibition effecicacy with the lowest log conidial concentration reaches 7.00 (spores/ml) 7 days after examination. Beside, the ability of inhibiting conidia germination of N. dimidiatum by these actinomycetes isolates was examined in laboratory condition with 5 replications. The result indicated that CT-LA4 isolate has the highest inhibition effecicacy with the lowest rate’s conidia germination reaches 17.82% 48 hours after inoculating.

Keywords: Actinomycetes, inhibiting sporulation, inhibiting conidia germination, Neoscytalidium dimidiatum, stem canker disease of Dragon fruit.