Jackfruit fruit rot disease is caused by Rhizopus sp. fungus that is one of the common diseases in jackfruit
fields in the Mekong Delta. The objective of this research was to examinate the actinomycetes able to antagonize
with Rhizopus sp. fungus causing fruit rot disease on Jackfruit. The antagonistic ability against Rhizopus sp.
fungus of 28 actinomycetes isolates were determined with 5 replications. The results found that 4 isolates (CBTG15, CL-TG3, CL-TG18 and CL-TG24) could reduce mycelia growth of fungus with radiuses of inhibition zones reaches 6.93mm; 6.87mm; 10.25mm and 8.58mm, respectively and antagonistic efficacy 58.15%; 59.18%;
60.42% and 63.12% , respectively at 48 hours after inoculation. On the other hand, the ability of inhibiting
sporulation of Rhizopus sp. by 4 actinomycetes (CB-TG15, CL-TG3, CL-TG18 and CL-TG24) isolates was checked in Laboratory condition with 4 replications. The result showed that CL-TG24 isolate have the highest
inhibition effecicacy with the lowest log conidia concentration reaches 5.898 (conidia/ml) at 4 days after testing. Beside, chitinase activity of 4 actinomycetes (CB-TG15, CL-TG3, CL-TG18 and CL-TG24) isolates was performed on chitin medium. The result indicated that, 4 actinomyces isolates had the chitinolytic activity and CL-TG24
isolate showed the highest chitinolytic activity with the chitin lyse halo radius of 21.75mm at 7 days after
examination.

Keywords: Actinomycetes, chitin, fruit rot disease on Jackfruit, Rhizopus sp.