Mycorrhizal associations and symbiotic propagation of two endangered Corunastylis (Orchidaceae)

Background. To effectively translocate threatened orchids it is recommended that they are propagated symbiotically with their mycorrhizal fungi. The terrestrial orchid genus Corunastylis has over 25 threatened species, yet there is no information on the identity of the mycorrhizal fungi or symbiotic propagation. Aims. To identify the mycorrhizal fungi associated with two endangered species, C. insignis and C. branwhiteorum, and determine effective symbiotic germination methods. Methods. Fungi were cultured from roots of Corunastylis at two sites for each species, one of which was shared between species. To estimate taxonomic diversity, 25 fungal isolates were sequenced and identified by comparison with known Operational Taxonomic Units’ (OTU’s) through a combination of phylogenetic analysis and sequence divergence at the ITS sequence locus. Further, we tested if germination varies between growth media, seed accession, and isolates of the same OTU of mycorrhizal fungus. Results. Both species formed mycorrhizal associations with Rhizoctonia (Ceratobasidiaceae), C. insignis with OTU T and U and C. branwhiteorum only with OTU U. We found that MOM medium led to significantly greater germination than MOB or MOB plus coconut (P<0.05). There was significant variation in germination between mycorrhizal isolates within the same putative species (OTU). Conclusions. Both species can be readily symbiotically germinated to adult plants using Rhizoctonia OTU T and U, significantly improving conservation options for these species. Implications. As isolates differ in their germination ability, we recommend ensuring that a range of isolates are included in symbiotic propagation for translocation to maintain diversity and potential to adapt to edaphic conditions.