Acacia mangium is an important plantation species in Vietnam providing industrial wood for domestic and export markets. Dying branches disease caused by Collectotrichum gloeosporioides is a serious threat to plantation productivity in North Vietnam. Antagonistic endophytes in A. mangium may have potential for inducing disease resistance to acacia pathogens. Branches of A. mangium with five disease levels (0: healthy tree, no damage; 1: 25 percent leaves and twigs of crown infected; 2: 25-50 percent leaves and twigs of crown infected; 3: 50-75 percent leaves and twigs of crown infected; 4: all leaves and twigs of crown infected) were collected at 4 plantation locations for isolating bacterial endophytes. Forty five strains of bacterial endophytes were isolated, of which 40 strains showed antifungal activity with Collectotrichum gloeosporioides. The number of endophytic strains varied with tree health. The strains that showed moderate to very strong antifungal activity were mostly isolated from healthy trees (disease level 0) or low disease impact (disease levell). Strains having strong and very strong antifungal activity were not found in A. mangium trees with high levels of disease (3 or 4). The density of bacterial endophytes isolated from the inner bark and phloem of A. mangium twigs varied from l x l0 exponent 5 to l3 x l0 exponent 5 CFU/gram. The highest density of endophytic bacteria was obtained in healthy trees.
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