Dynamics of symbiotic fungal diversity in roots of Dendrobium devonianum seedlings at different developmental stages

Abstract:

[Background] Orchids form a close symbiotic relationship with mycorrhizal fungi throughout their life cycle. The symbiotic fungi provide essential nutrients during seed germination and seedling establishment of orchids. [Objective] To reveal the diversity and dynamics of the endophytic (symbiotic) fungi of Dendrobium devonianum seedlings at different developmental stages. [Methods] The seedlings of D. devonianum were developed from in situ symbiotic seed germination, and the root samples were collected from the seedlings two, three, four, and six months after germination, respectively. Amplicon sequencing was employed to analyze the fungal community composition, abundance, and diversity. [Results] A total of 944 amplicon sequence variants (ASVs) were obtained from roots of seedling at all the four stages, belonging to 218 genera, 144 families, 71 orders, 24 classes of 5 phyla. The dominant fungal genera in D. devonianum seedlings of two to four months were Serendipita, Talaromyces, and Curvularia, respectively, while Talaromyces and Sebacina were dominant in the roots of six-month-old seedlings. The dominate symbiotic fungi underwent two shifts during seedling development. The first switch was from Tulasnella to Serendipita in the seedlings less than two months old and the second was from Serendipita to Sebacina in the seedlings of four to six months old. [Conclusion] The fungi in D. devonianum seedlings experience dynamic changes. The seedlings may actively choose the most compatible fungal partners or may be passively associated with the mycorrhizal fungi with high relative abundance in the environment. These new insights into the dynamics of symbiotic fungi during orchid seedling development offer a scientific basis to isolate fungal strains that might be employed to promote the growth and improve the survival of D. devonianum seedlings.