Abstract
Mycorrhizal interactions of orchids are influenced by several environmental conditions. Hence, knowledge of mycorrhizal fungi associated with orchids inhabiting different ecosystems is essential to designing recovery strategies for threatened species. This study analyzes the mycorrhizal associations of terrestrial orchids colonizing grassland and understory in native ecosystems of the region of La Araucanía in southern Chile. Mycorrhizal fungi were isolated from peloton-containing roots and identified based on the sequence of the ITS region. Their capacities for seed germination were also investigated. We detected Tulasnella spp. and Ceratobasidium spp. in the pelotons of the analyzed orchids. Additionally, we showed that some Ceratobasidium isolates effectively induce seed germination to differing degrees, unlike Tulasnella spp., which, in most cases, fail to achieve protocorm growth. This process may underline a critical step in the life cycle of Tulasnella-associated orchids, whereas the Ceratobasidium-associated orchids were less specific for fungi and were effectively germinated with mycorrhizal fungi isolated from adult roots.
Highlights
The symbiotic relationship established between orchids and their compatible mycorrhizal fungi is characterized by the dependence of the plant on fungal carbon (C) and other mineral nutrients essential to start the initial developmental stages [1,2,3]
13 terrestrial orchids belonging to the genera Chloraea, Gavilea and Codonorchis were found at the 11 different sampling sites considered for our analyses
Despite mycorrhizal fungi associated with terrestrial orchids having been previously identified, such studies have reported a high diversity of orchid mycorrhizal fungi (OMF) associated with the target plants, including mycorrhizal and non-mycorrhizal fungal endophytes, which agrees with the results obtained in our study [19,22,32]
Summary
The symbiotic relationship established between orchids and their compatible mycorrhizal fungi is characterized by the dependence of the plant on fungal carbon (C) and other mineral nutrients essential to start the initial developmental stages [1,2,3]. These mechanisms are called mycoheterotrophy and describe the ability of the plant to obtain C from intracellular fungal hyphae [4]. A conserved characteristic is the formation of a symbiotic structure named peloton, which corresponds to hyphal coils where the metabolic interchange between symbionts occurs in both protocorm and mycorrhizal roots [1,14]
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