In situ seedling baiting to isolate plant growth-promoting fungi from Dendrobium officinale, an over-collected medicinal orchid in China

Orchids highly depend on mycorrhizae for survival and growth. Traditionally, to obtain orchid mycorrhizal fungi (OMFs) for plant growth, fungi have been isolated from the roots of mature wild plants; however, fungal partners engaged may change through plant ontogeny, and for those of orchid species that have been over-collected to extirpation, it’s almost impossible to take samples of wild plants. In this study, we developed the idea of using in situ seedling baiting to capture seedling growth-promoting fungi from Dendrobium officinale, an over-collected medicinal orchid in China. In vitro-produced seedlings of D. officinale were transplanted into their original habitats. Newly established roots were sampled six times during one year, and five Tulasnella species and one Fusarium species were obtained and identified morphologically and molecularly. Three Tulasnella isolates used for in vitro inoculation of D. officinale seedlings showed different impact on seedling growth, despite their close phylogenetic relatedness. One Tulasnella isolate showed a strong ability to promote seedling growth and could be selected for use in restoration plantings of D. officinale. Our results suggest that using in situ seedling baiting technique could be an efficient way to obtain seedling growth-promoting fungi, and this approach could have broad applications in orchid mycorrhiza studies and orchid conservation