齿瓣石斛不同月龄幼苗根内共生真菌多样性动态变化分析

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

摘要:

【背景】兰科植物整个生命周期都与真菌形成密切的共生关系，种子萌发、幼苗形成等关键发育阶段都需要共生真菌为其提供营养。【目的】探究齿瓣石斛(Dendrobium devonianum)不同月龄幼苗共生真菌多样性及其变化规律。【方法】基于种子-真菌野外直播技术获得齿瓣石斛不同月龄幼苗并采集根样品，采用扩增子测序技术研究共生真菌群落组成、相对丰度及多样性。【结果】齿瓣石斛2‒6月龄幼苗中共有944个扩增子序列变体(amplicon sequence variant, ASV)，隶属5门24纲71目144科218属。2‒4月龄幼苗的优势真菌为无孢蜡壳属(Serendipita)、篮状菌属(Talaromyces)和弯孢属(Curvularia)，6月龄幼苗的优势真菌为篮状菌属和蜡壳耳属(Sebacina)。优势共生真菌类群在幼苗期发生了2次转变，即2月龄前由胶膜菌属(Tulasnella)转变成无孢蜡壳属；6月龄期由无孢蜡壳属转变成蜡壳耳属。【结论】齿瓣石斛幼苗发育过程中对于共生真菌的选择是一个动态过程，可能是主动选择环境中的最适真菌，亦或是被动选择了环境中相对丰度较高的真菌。这一结果为了解齿瓣石斛不同发育阶段共生真菌群落的多样性和动态变化提供了新的证据，并为分离获得促进幼苗生长、提高幼苗成活率的关键真菌类群提供了科学依据。

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.