Abstract:In order to understand the symbiotic relationship between Epulorhiza sp. and the roots of Dendrobium officinale, and also to make certain the influence of Epulorhiza sp. on root morphology, the roots of D. officinale were irrigated with liquid cultured Epulorhiza sp., the changes in phenotype and ultrastructure of roots were observed after three months. The results showed that the cortical cells of root were invaded by mycelia, which induced the formation of mycelium group to form a symbiotic relationship between Epulorhiza sp. and the roots. The content of IAA in root increased after co-cultured with Epulorhiza sp., and the lateral roots were induced for increasing root volume, as well as the root vitality was significantly improved. Therefore, Epulorhiza sp. co-cultured with the roots of D. officinale not only could generate mycorrhizal to establish a symbiotic relationship, but also the symbiotic mycelium could colonize in roots, induced the changes in root structure, and the formation of lateral root played an important role in growth of D. officinale.