Cold-moist stratification improves germination in a temperate terrestrial orchid

Seed dormancy is a common evolutionary adaptation in temperate plant taxa. Dormancy mechanisms can prevent seeds from germinating at inopportune times, such as a cold period. We report the influence of pregermination stratification treatments on in vitro seed germination and seedling development in Platanthera chapmanii, a rare temperate terrestrial orchid native to the southeastern USA. Seeds were subjected to 0, 8, or 12 wk of cold-moist stratification at 5°C; mean seed viability was 89%. At 9 mo after plating, seeds exposed to 8 and 12 wk of stratification resulted in higher germination (Stage 1; 32% and 35%, respectively) in comparison to 25% germination in nonstratified seeds. Once a protocorm developed a leaf primordium (i.e., reached Stage 2), development to Stage 3 (root development) was independent of the pregermination treatments. Exposure to artificial lights for 3, 4, and 5 mo resulted in 32%, 44%, and 63% of the Stage 2 seedlings, respectively, developing into Stage 3 photosynthetic root-bearing seedlings. Our results indicate that in vitro seed germination in this temperate terrestrial orchid can be improved by using cold stratification. Furthermore, leaf- and root-bearing seedlings can be obtained through the methods reported herein.