Fluridone Stimulates in Vitro Seed Germination of a Rare Hardy Terrestrial Orchid (platanthera Leucophaea)

Seeds of temperate terrestrial (hardy) orchids are considered more difficult to germinate compared to their tropical epiphytic counterparts, presumably because they have higher levels of abscisic acid (ABA) in their seed coats which prevents seeds from germinating prematurely during winter dormancy. In nature, ABA is gradually broken down (stripped) by natural weathering, triggering germination. This process can be shortened artificially, however, by using chemical bleaching agents and cold-moist stratification with mixed results. In this study, we explored the use of fluridoneto break seed dormancy in a hardy orchid native to North America, Platanthera leucophaea (Nutt.) Lindl. This organic compound (IUPAC name: 1-methyl-3-phenyl-5-[3-(trifluoromethyl) phenyl] pyridin-4(1H)-one) is a commercial herbicide that inhibits ABA biosynthesis. We added fluridone directly to agar media prior to seed sowing in vitro. Both symbiotic and asymbiotic germination techniques were applied that involved two different agar media, with and without added fluridone. Symbiotic germination was carried out using standard oatmeal agar inoculated with a mycorrhizal fungus (Ceratobasidium), whereas asymbiotic treatments utilized P723 agar medium. Seedling development within some of the replicate plates progressed to Stage 3 in all treatments, but development was marked in all asymbiotic plates containing fluridone leading to leaf elongation, 385 days after sowing. As an herbicide, fluridone’s use as a media additive to propagate a rare photosynthetic orchid seems counterintuitive, but its use in vitro to stimulate seedling development has the potential to benefit conservation efforts for this and possibly other hardy orchid species.