Abstract: Intestinal bacteria of the Callimenellus fumidus Walker were isolated and purified by the dilution coating method and identified by a combination of morphological and molecular biological methods;at the same time, their antagonistic activity against plant pathogenic fungi was determined by the dual culture method,and the antifungal efficacy of the extracts of the fermentation products of the acvtive intestinal bacteria on plant pathogenic fungi was further evaluated by the mycelial growth rate method. The results showed that 76 culturable bacterial strains were isolated from the intestines of C. fumidus Walker,of which 11 strains were identified through morphological and molecular biological methods as belonging to 9 different genera,including Leucobacter, Microbacterium, Cellulosimicrobium, Arthrobacter, Lysinibacillus, Staphylococcus, Atlantibacter, Klebsiella and Enterobacter. The strain Klebsiella oxytoca BS.X3-A1 was found to have antagonistic activity against all the 9 test pathogens as determined by dual culture method. The inhibitory activity of the fermentation product of the strain against the 9 test pathogens was further determined. At a concentration of 4 g/L,the inhibition rates against Ceratocystis paradoxa,Pestalotiopsis theae,Alternaria citri,Cochliobolus miyabeanus,and Alternaria oleracea all reached 100%. The inhibition rates against anthracnose caused by Colletotrichum capsici,Diaporthe citri and Exserohilum turcicum exceeded 80%, while the inhibition rate against Phytophthora parasitica var. Nicotianae was relatively weaker at 54.68%. The virulence of the strain BS.X3-A1 against 9 phytopathogenic fungi was determined and found to have EC₅₀ values ranging from 0.394 8 to 3.908 9 g/L. Among them,it exhibited the strongest antifungal activity against Ceratocystis paradoxa with EC₅₀ values of 0.394 8 g/L,which was less than 0.5 g/L, followed by Pestalotiopsis theae and Alternaria citri with EC₅₀ values of 1.132 0 and 1.326 8 g/L,respectively both below 1.5 g/L. In addition,it also showed good antifungal activity against Exserohilum turcicum,Cochliobolus miyabeanus,and Diaporthe citri with EC₅₀ values of 2.225 6,2.226 3,and 2.327 2 g/L,respectively,which were all less than 3 g/L;while the antifungal activities against Alternaria oleracea and Phytophthora parasitica var. Nicotianae were relatively weaker,with EC₅₀ values of 3.071 8 and 3.908 9 g/L,respectively. The results showed that the intestine of C. fumidus Walker harbors bacteria with antifungal activity against plant pathogenic fungi,and these intestinal bacteria produce secondary metabolites effective against plant pathogenic fungi. The results of the study provide a reference for further exploration of antifungal compounds derived from the intestinal bacteria of the C. fumidus Walker.

Key words: Callimenellus fumidus Walker, intestinal bacteria, isolation and identification, plant pathogenic fungi, antifungal activity