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

De-Yun Chen,Xin-Ju Wang,Tai-Qiang Li,Neng-Qi Li,Jiang-Yun Gao

doi:10.1016/j.gecco.2021.e01659

Abstract

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.

Highlights

Orchids are highly dependent on mycorrhizae for survival and growth
Our results suggest that using an 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
Motivated by the success of in situ/ex situ seed baiting, in this study, we developed the idea of using in situ seedling baiting to obtain seedling growth-promoting fungi, in which in vitro-produced seedlings of D. officinale were transplanted into their original habitats, and newly established roots of well-growing plants were sampled for fungal isolation

Summary

Introduction

Orchids are highly dependent 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; the species of OMF may change as the plants undergo different developmental stages. For medicinal Dendrobium species, the Shi-Hu industry has developed rapidly in southern China since the 1990s as a result of massive commercial cultivation; due to doubts about the quality and efficacy of the products obtained with this cultivation method, the lack of product standards and the low quantities of products, the utilization of these products in TCM is limited [6]. Such massive commercial cultivation has not alleviated pressure on wild populations, according to recent surveys on the orchid trade in China [7]. To balance the conservation of threatened Dendrobium species and the continuing demand for wild-grown materials, a restoration-friendly cultivation model for medicinal orchids, especially Dendrobium species, has been proposed, in which orchids are planted in natural settings[3, 8]; this method is considered promising for linking the commercial TCM industry with biodiversity conservation initiatives in China [6]

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