In Vitro Symbiotic Germination: A Revitalized Heuristic Approach for Orchid Species Conservation

Abstract

As one of the largest families of flowering plants, Orchidaceae is well-known for its high diversity and complex life cycles. Interestingly, such exquisite plants originate from minute seeds, going through challenges to germinate and establish in nature. Alternatively, orchid utilization as an economically important plant gradually decreases its natural population, therefore, driving the need for conservation. As with any conservation attempts, broad knowledge is required, including the species’ interaction with other organisms. All orchids establish mycorrhizal symbiosis with certain lineages of fungi to germinate naturally. Since the whole in situ study is considerably complex, in vitro symbiotic germination study is a promising alternative. It serves as a tool for extensive studies at morphophysiological and molecular levels. In addition, it provides insights before reintroduction into its natural habitat. Here we reviewed how mycorrhiza contributes to orchid lifecycles, methods to conduct in vitro study, and how it can be utilized for conservation needs.

Orchid mycorrhizal fungi and ascomycetous fungi in epiphytic Vanda falcata roots occupy different niches during growth and development

“…However, many orchid species are listed as endangered owing to habitat degradation and dependence on other organisms, i.e., pollinators (Suetsugu et al 2015;Freitas et al 2020). Moreover, establishing orchids in the natural habitat is always complicated, even in suitable conditions (Pujasatria et al 2020). Due to its unique, one-of-a-kind traits, orchid seed germination is often hard to occur naturally.…”

“…Consequently, orchids' seeds are nearly impossible to germinate without nutritional support. For seeds to successfully germinate and grow into mature plants, they must establish orchid mycorrhizal (OM) symbiosis (Arditti and Ghani 2000; Barthlott et al 2014;Yeh et al 2019;Pujasatria et al 2020). Colonization of orchid mycorrhizal fungi (OMF) starts at seed germination and may last until adulthood.…”

Regulation of balanced root fungal community of Vanda falcata (Orchidaceae) by partitioning its mycorrhizal fungi and ascomycetous fungi across growth and development

“…Most orchids associate with Rhizoctonia- like fungi, a broad term for several genera resembling the anamorphic morphology of Rhizoctonia . As symbionts, there are three genera in this group: Ceratobasidium, Serendipita (often associated with Sebacina sensu lato ), and Tulasnella (Rasmussen et al 2015; Yeh et al 2019; Pujasatria et al 2020). Originally, those fungi are saprophytic, endophytic, or even pathogenic.…”

“…Originally, those fungi are saprophytic, endophytic, or even pathogenic. However, among those genera, many species were isolated from orchid roots and proved to be mycorrhizal upon co-inoculation with seeds of respective orchid species (Pujasatria et al 2020).…”

The challenges of growing orchids from seeds for conservation: An assessment of asymbiotic techniques

“…Mycorrhizal dependency is the largest hurdle to overcome in orchid propagation as the mycorrhizae provide most of the minerals, nutrients, vitamins, and water needed for germination and seedling development (Herrera et al, 2019 ) and vary in the specificity of their relationship with their orchid hosts (McCormick et al, 2018 ; Li et al, 2021 ). In vitro symbiotic germination has been used for orchid propagation (Pujasatria et al, 2020 ), however, successful propagation requires extensive knowledge of the specific orchid–mycorrhizal interaction, as well as the ability to isolate and grow the fungus, which can take considerable time and effort. Mycorrhizae isolated from the roots of mature plants may not be suitable for inducing seed germination (McCormick et al, 2021 ; Zhao et al, 2021 ), and many orchid mycorrhizal fungi are unculturable axenically, making symbiotic germination impossible (Li et al, 2021 ).…”