[Isolation, classification and antimicrobial activity of endophytic actinomycetes from plant leaves]

Leave samples of Paeonia lactiflora and Trifalium repens were collected from Sichuan Province and Beijing respectively to study their endophytic actinmycetes. After a well-established surface-sterilized procedure, the samples were plated on agar media of TWYE, HV, YECD, NA and WA, followed by incubation at 28 degrees C for 2 - 4 weeks. With the help of light microscope, 15 actinomycetes strains were isolated from the plates. Comparison of cultural features and fingerprinting analyses of BOX-PCR products were performed to cluster the isolates, with the result that all the strains were assigned to 12 different genotypes, half of them from Paeonia lactiflora and half from Trifalium repens. A combination of morphological and 16S rRNA gene sequence data showed that except strains C4 and C5, which belonged to Pseudonocardia, 13 of the isolates were streptomycetes. Most isolates share high 16S rRNA gene sequence similarities to known type strains. However, strain C12 shares low values, 96.6% in maximum, and strain C5 shares 97.9% in maximum; more assays are needed to ascertain their taxonomic positions. In the tests of antimicrobial activity against 7 bacteria, 3 fungi and 1 yeast, 11 isolates were positive in one or more tests, and 55% of the positive ones could inhibit the growth of Rhizoctonia solani, a significant pathogen of plants.