The challenges of growing orchids from seeds for conservation: An assessment of asymbiotic techniques

Abstract

Lewis Knudson first successfully germinated orchid seeds asymbiotically on artificial medium in 1922. While many orchid species have since been grown asymbiotically, the tremendous variation in how species respond to artificial medium and growth conditions ex situ has also become apparent in the past century. In this study, we reviewed published journal articles on asymbiotic orchid seed germination to provide a summary of techniques used and to evaluate if these differ between terrestrial and epiphytic species, to identify areas where additional research is needed, and to evaluate whether asymbiotic germination could be used more often in ex situ conservation. We found articles reporting successful asymbiotic germination of 270 species and 20 cultivars across Orchidaceae. Researchers often used different techniques with epiphytic versus terrestrial species, but species-specific responses to growth media and conditions were common, indicating that individualized protocols will be necessary for most species. The widespread success in generating seedlings on artificial media suggests that asymbiotic techniques should be another tool for the conservation of rare orchid species. Further advances are needed in understanding how to introduce mycorrhizae to axenically grown orchids and to maximize the viability of seedlings reintroduced into natural habitats to fully utilize these methods for conservation.

Keywords: Orchidaceae; asymbiotic; disinfection; ex situ; germination; growth medium; seed; stratification.

Figure 1

Number of articles on asymbiotic germination of orchid seeds published by year that were reviewed for this study. Data for 2021 are through May 26, 2021.

Figure 2

Variation between epiphytic and terrestrial species in storage and chilling of seeds prior to sowing. Studies reporting use of a stratified treatment were included as chilled.

Figure 3

Variation between epiphytic and terrestrial species in (A) disinfection unit (capsules or seeds) and (B) disinfection method used. Hypochlorite includes the use of calcium hypochlorite, sodium hypochlorite, and commercial bleach. See text for other disinfecting agents that were used.

Figure 4

Variation between epiphytic and terrestrial species in the light environment used for germination.

Figure 5

(A) Media reported across all studies reviewed and (B) differences in media reported for at least 2% of studies of epiphytes or terrestrial species. BM‐1 and BM‐2 are very similar media and were counted together for this figure.