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Australian Journal of Botany Australian Journal of Botany Society
Southern hemisphere botanical ecosystems
RESEARCH ARTICLE

Asymbiotic germination of Prasophyllum (Orchidaceae) requires low mineral concentration

Marc Freestone https://orcid.org/0000-0001-8736-6459 A B * , Celeste Linde https://orcid.org/0000-0002-8207-1202 B , Nigel Swarts https://orcid.org/0000-0002-4527-7658 C and Noushka Reiter https://orcid.org/0000-0001-8450-2769 A B
+ Author Affiliations
- Author Affiliations

A Royal Botanic Gardens Victoria, Science Division, Corner of Ballarto Road and Botanic Drive, Cranbourne, Vic. 3977, Australia.

B Ecology and Evolution, Research School of Biology, The Australian National University, Canberra, ACT 2600, Australia.

C Tasmanian Institute of Agriculture, The University of Tasmania, Sandy Bay, Tas. 7005, Australia.

* Correspondence to: marc.freestone@gmail.com

Handling Editor: Susanna Venn

Australian Journal of Botany 71(2) 67-78 https://doi.org/10.1071/BT22116
Submitted: 11 October 2022  Accepted: 14 February 2023   Published: 13 March 2023

© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing

Abstract

Context: Asymbiotic germination is used for propagation of orchids and to assess seed viability. However, asymbiotic germination media remain undeveloped for Prasophyllum (Orchidaceae), a genus with 39 threatened species in southern Australia.

Aims: To develop asymbiotic germination and replate media for Prasophyllum, and determine whether survival of asymbiotically grown seedlings under nursery conditions is enhanced through the addition of a mycorrhizal fungus to potting media.

Methods: Using Prasophyllum frenchii as a model, we tested 81 asymbiotic germination medium combinations. The three best-performing media were then compared against four untested commercial media, with and without added coconut water and/or banana. The best-performing medium was trialled on 18 additional Prasophyllum species. Twenty-four replate media were then tested for their ability to support seedling development. We measured the survival of seedlings under nursery conditions with and without the addition of mycorrhizal Ceratobasidium fungus to potting media.

Key results: Low concentrations of minerals, auxins and cytokinins were necessary for asymbiotic germination of P. frenchii, although germination was highest overall on the commercial medium W9.5 with 5% coconut water. The most effective replate medium was W9 with 5% banana. However, survival of seedlings was 1.7%, 2 years after transferral to potting media in the nursery, regardless of the addition or absence of a mycorrhizal fungus.

Conclusions: Asymbiotic media can effectively germinate Prasophyllum seed, although deflasked seedlings have low survival rates.

Implications: Our media are broadly applicable to assess seed viability in Prasophyllum. However, poor survival of asymbiotically grown seedlings contrasts with recently published evidence of high seedling survival using symbiotic propagation methods, indicating that plants should be propagated symbiotically for conservation programs.

Keywords: asymbiotic, conservation, germination, nutrient, orchid, Prasophyllum, propagation, seed viability.


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