Abstract
Orchid mycorrhizal fungi (OMF) are critical for seed germination and maintaining natural populations of orchids, yet the degree of specificity of most orchids to their mycorrhizal associates remains unknown. Many orchids are at risk of extinction, whether generalists or specialists, but orchid species of narrow fungal specificity are arguably under increased threat due to their requirement for specific fungal symbionts. This study characterises the fungi associated with Aerangis ellisii, a lithophytic orchid from a site in the Central Highlands of Madagascar. Culturable OMF isolated from spontaneous protocorms of this species from the wild were used for seed germination. In vitro germination and seedling development of A. ellisii were achieved with fungi derived from A. ellisii and an isolate from a different Aerangis species 30 km away. The significance of these findings and their importance to conservation strategies for this species and other Aerangis spp. is discussed. These results have important implications for the conservation of A. ellisii populations in Madagascar.
Highlights
Madagascar is a well-known biodiversity hotspot to which 90% of its 1000 orchid species are endemic (Tyson 2000)
Our goal is to enhance the conservation of A. ellisii and other rare lithophytic orchids by understanding seed germination requirements leading to more effective propagation from seed
To investigate which fungal isolates are capable of germinating A. ellisii seeds, we sampled 30 seedling/mature plants of A. ellisii and related species across three sites in Madagascar including other orchid species in their vicinity
Summary
Madagascar is a well-known biodiversity hotspot to which 90% of its 1000 orchid species are endemic (Tyson 2000). What was once a continuum of natural vegetation blanketing the world’s 4th largest island has been converted mostly to farmland except in the most remote and inaccessible areas. Jacksonville, IL 62650, USA 3 Faculty of Natural Sciences, Department of Life Sciences, Silwood. Orchids on isolated rocky outcrops in the Central Highlands of Madagascar (CHM), for example, appear to suffer from inbreeding depression. Their specific pollinators (e.g. hawkmoths) may be less common and/or they must fly considerable distances to forage on nectar, possibly explaining why few capsules are produced among the species that cater to moths (e.g. Aerangis, Angraecum), and why a high proportion of their seeds often lack embryos (Kendon et al 2017). With limited cross-pollination, fewer spontaneous seedlings are generated per year resulting in steady population decline over time
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