Identification of fungal associates of the swamp helmet orchid (Corybas Carsei), a threatened (nationally critical) species

Abstract

ABSTRACT Corybas carsei is one of New Zealand’s most endangered orchids, with a single remaining population in the Whangamarino Wetland (North Island). Although orchid mycorrhizae have proved a critical aspect of orchid conservation globally, until now mycorrhizal fungi of C. carsei have not been identified or utilised for conservation. This study investigated fungal associates of C. carsei using three culture-based approaches: fungi grown directly from fragments of root tissue, from pelotons isolated from root-collars, and directly from macerated protocorm tissue. Fungi were cultured and identified as a diverse array of fungi through Sanger sequencing of the internal transcribed spacer region. This included the fungus Pleurotus purpureo-olivaceus (Basidiomycota; Agaricales), which belongs to a genus containing putative orchid mycorrhizal fungi, and the ericoid mycorrhizal fungus Oidiodendron eucalypti (Ascomycota; Leotiomycetes incertae sedis). No Rhizoctonia-like fungi, typical of orchid mycorrhizae, were found through any approach and fungi cultured in the present study likely represent endophytes, rather than mycorrhizal fungi. The potential of C. carsei having unculturable mycorrhizal associations, and the challenge this presents to conservation efforts, is discussed.