Seed dormancy type and germination requirements of Codonopsis javanica subsp. javanica , a medicinal plant from subtropical China

This study investigated the seed dormancy and germination characteristics of Codonopsis javanica subsp. javanica , a species native to subtropical evergreen broad-leaved forests in China. We measured the embryo - seed (E:S) length ratio in freshly dispersed seeds and in seeds at the stage of seed coat split before radicle emergence. We also examined the effects of light conditions (light vs. dark) and dry after-ripening (DAR) treatment on seed germination under five constant temperatures (5, 10, 15, 20 and 25°C) and two alternating temperature regimes (15/5 and 25/15°C). Our results showed that C. javanica subsp. javanica seeds possess underdeveloped embryos that grow internally prior to germination, with the E:S ratio increasing by 33%. Fresh seeds germinated well (> 95%) only under relatively high temperatures (20, 25 and 25/15°C) in light, whereas germination was strongly inhibited at lower temperatures and in dark. Six months of DAR effectively broke seed dormancy, significantly increasing the germination rate (GR) and the final germination percentage (FGP) at low temperatures in light, as well as significantly improving FGP at high temperatures in dark. Following dormancy release, the temperature range for germination expanded from high to low temperatures, and the light requirement for germination at high temperatures was significantly reduced. We conclude that freshly dispersed seeds of C. javanica subsp. javanica exhibit non-deep simple morphophysiological dormancy. These findings provide an effective and low-cost method for propagating this species for medicinal purposes, thereby contributing to the conservation of wild populations.