Do the fungi associated with roots of adult plants support seed germination? A case study on Dendrobium exile (Orchidaceae)

To obtain compatible fungi for symbiotic seed germination is a key step for seed-based orchid conservation. This is particularly important to the practice of restoration-friendly cultivation for conserving over-collected medicinal orchids, for example, many species of Dendrobium in China. In this study, we comparatively investigated the effects of fungi from roots and protocorms/seedlings on seed germination, protocorm formation and seedling development in Dendrobium exile. A total of 7 different fungal species were obtained, including three rhizoctonia fungi (Tulasnella sp. DerIV, Tulasnella sp. DerV and Tulasnella sp. DesI), three non-rhizoctonia fungi (Nodulisporium sp. DerI, Xylaria plebeja DerII, Colletotrichum sp. DerIII) and one unidentified fungus DesII. Among the three rhizoctonia fungi, DesI isolated from seedlings was more efficient at supporting seed germination up to seedlings than the two fungi (DerIV and DerV) isolated from adult roots. At 45 days of incubation, 70.93 ± 6.92% of seeds developed into seedlings in DesI treatment, while no seedlings were developed in the DerIV and DerV treatments. Our results indicated that orchids may need different fungal partners for seed symbiotic germination vs. adult plant development. The diverse fungi residing in the roots could have potentially diverse functions. Keywords: Dendrobium, Mycorrhizal fungi, Restoration-friendly cultivation, Symbiotic seed germination, Orchid conservatio