Abstract: Based on previous studies, citrus endophytic fungus Nemania sp. LJZ-Y-11 was selected for fermentation, extract preparation and evaluation of its antimicrobial activity, aiming to lay a foundation for the development and utilization of its metabolites. The antifungal and antibacterial activities of the ethyl acetate extract were determined by using a mycelium growth rate method and toxic medium coating method, respectively. The results showed that the ethyl acetate extract of LJZ-Y-11 exhibited an excellent antifungal activity against most of tested plant pathogenic fungi, and had an antibacterial activity against 10 animal pathogens to some extent. The inhibitory rate against 9 plant pathogenic fungi were all more than 50% at 2.5 g/L of the extract. Moreover, except that the inhibitory rate against Alternaria citri was 56.52%, the others were 100%. The toxicity of extract against 8 plant pathogenic fungi was determined furtherly, with EC₅₀ values ranging from 0.004 8 g/L to 0.154 4 g/L. There was the highest inhibitory activity against Exserohilum turcicum, Diaporthe citri and Phytophthora parasitica var. nicotianae with EC₅₀ values of 0.004 8, 0.005 3 and 0.006 7 g/L, respectively, less than 0.01 g/L, following by Colletotrichum capsici, Pestalotiopsis theae and Ceratocystis paradoxa with EC₅₀ values of 0.022 7, 0.035 6 and 0.067 9 g/L, respectively, less than 0.1 g/L; and also had a significant inhibitory activity against Alternaria oleracea and Cochliobolus miyabeanus with EC₅₀ values of 0.101 3 g/L and 0.154 4 g/L, respectively. In addition, the extract also showed significant antibacterial activities against 10 animal pathogens with MIC values of 0.078 1-2.5 g/L. There were high inhibitory activities against Bacillus subtilis, Escherichia coli, Staphylococcus aureus, Bacillus cereus, Bacillus anthraci and Monilia albican with MIC values of less than 0.2 g/L, and had the highest inhibitory activity against Bacillus subtilis with a MIC value 0.078 1 g/L. There were also strong inhibitory effects against Bacillus megaterium and Micrococcus lysodeikticus, with a MIC value of 0.625 g/L. The inhibition activity against Enterobacter aerogenes and Salmonella typhi was relatively weaker, with MIC values of 2.5 g/L. The results in this study reveal that the secondary metabolites of LJZ-Y-11 has broad-spectrum and significant antimicrobial activity against the common pathogens, providing a useful experiment basis for the development and utilization of the secondary metabolites as biological antimicrobial agents.

Key words: citrus endophytic fungi, Nemania sp. ethyl acetate extract, antimicrobial activity