In vitro propagation of temperate Australian terrestrial orchids: Revisiting asymbiotic compared with symbiotic germination

Abstract

Using a common temperate herbaceous terrestrial orchid from Australia (Caladenia latifolia) this study investigated 19 asymbiotic media variations comprising four commonly used basal media [half-strength Murashige and Skoog (1/2MS), Knudson C (KC), Pa5, and Vacin and Went (VW), with combinations of the plant growth regulators 6-benzylaminopurine (BA) and α-naphthalene acetic acid (NAA) or coconut water (CW) and compared their performance with germination on a standard symbiotic germination medium, oatmeal agar (OMA). Percentage germination of seeds every 2weeks for a total of 8weeks (five replicates per treatment), time to germination, and growth and development phases in seedlings were recorded. 1/2MS with 5% (v/v) fresh CW delivered 93% germination, with seedling vigour and development indistinguishable from OMA (95% germination). The same protocol was applied to a further ten species (including the endangered Caladenia huegelii), demonstrating high asymbiotic germination performance (60-93%) across a wide phylogenetic range of terrestrial orchid species.