The research was conducted in the Plant disease Laboratory, College of Agriculture, Can Tho University to screen actinomycetes isolates able to control decline disease in Mandarin orange caused by Phytophthora sp. fungus. The antagonistic ability against Phytophthora sp. fungus of the actinomycetes isolates were determined with 5 replications under laboratory condition. The results found that 4 actinomycetes isolates BM5-VL, BT5-VL, PH30-HG and PH37-HG showed higher stabler antagonistic ability with radiuses of inhibition zones reaches 1.27cm; 1.45cm, 1.55cm and 1.35cm, respectively and antagonistic efficacy reaches 64.32%; 68.27%; 70.46% and 62.36%, respectively at 6 days after inoculation. The β-glucan degradation potential of 4 actinomycetes isolates (BM5-VL, BT5-VL, PH30-HG and PH37-HG) was conducded with 5 replications. The result indicated that the actinomyces isolate BT5-VL showed the highest β-glucanolytic activity with the β-glucan lyse halo radius of 2.05 cm at 14 days after examination. Beside, cellulose degradation potential of these actinomycetes isolated were examined with 5 replications under laboratory condition. The results indicated that, the actinomyces isolate BT5-VL has expressed the cellulolytic activity with the cellulose lyses halo radius of 2.18 cm at 7 days after testing.

Keywords: Actinomycetes, cellulose, decline disease in Mandarin orange, Phytophthora sp., β-glucan.