Utilising Indigenous Fungi in Non-Sterile Microcosms for Rapid and Efficient Propagation of Endangered Caladenia Species (Orchidaceae)

The temperate terrestrial Australasian orchid genus Caladenia has 181 taxa in Western Australia, including 23 endangered species. They have relatively specific pollinators and fungi, so are difficult to propagate and conserve. This project focuses on three threatened Caladenia species from isolated habitats in the Western Australian wheatbelt. Despite many attempts to optimise orchid propagation methods, inexact and inconsistent success criteria make comparisons of them difficult. Our aims were to measure the efficiency, complexity and effectiveness of propagation methods for rare and common Caladenia species, document their development in relatively natural conditions and produce robust plants for translocation. We utilised three orchid seed germination methods (1) in vitro asymbiotic synthetic agar media without fungi, (2) ex situ seed baiting over concentrated soil organic matter (OM), and (3) a novel method using permeable pouches in non-sterile substrates containing OM from orchid habitats (the FORGE system). Methods were compared by measuring growth rates and survival of protocorms and seedlings. There were major differences between methods and species. In vitro asymbiotic germination on Petri plates produced many protocorms, but only a few survived explanting. Protocorms from non-sterile methods were substantially more resilient in the incubator or greenhouse. The FORGE system was most efficient, as seedlings grew 20 times faster and could be moved to new pouches for further growth. Seed baiting protocorms also survived in pouches. Several stages of growth in pouches produced large seedlings with tuber initiation, suitable for outplanting that year. Our observations lead to refined definitions of growth stages and success criteria for orchid propagation. We recommend further development of FORGE systems for efficiently producing orchid seedlings pre-adjusted to growth in nature, especially for conservation. This system also has great potential for fungal isolation and morphological or physiological studies, based on orchid development in near-natural conditions.