Abstract: Amplified fragment length polymorphism (AFLP) was used to study diversity of 19 representative mycorrhizal Rhizoctonia strains, which isolated from 7 species Chinese orchids (Cymbidium) distributed in different sites and belonged to different ecologic types. A high degree of diversity was found among the mycorrhizal Rhizoctonia strains. 1 869 bands were got by using 12 pairs of AFLP primers, and among them 1 016 bands were polymorphism, the mean percentage of polymorphism was 54.4%, which indicated that AFLP was a greatly efficient method to study the diversity of mycorrhizae of Chinese orchids (Cymbidium). The AFLP results were analyzed for similarity among strains via unweighted pair-group means cluster analysis, Similarity among 19 mycorrhizal Rhizoctonia strains ranged from 0.61 to 0.89. Cluster analysis among the mycorrhizal strains showed 3 crucial factors, the distributed environments，orchids species and ecologic type of orchids, which affected the diversity of Chinese orchids (Cymbidium) symbiotic mycorrhizae and the speciality-relation between mycorrhizae and hosts. And the terrestrial orchids belong to Cymbidium goeringii and epibiosis orchids of Yunan province showed strongly strict speciality-relation with the stains isolated from them.

Key words: Cymbidium, mycorrhizal-fungi, AFLP, diversity