Physiological epicotyl dormancy and its alleviation in seeds of Yunnanopilia longistaminea: the first report of physiological epicotyl dormancy in China.

Yunnanopilia longistaminea is an endangered monotypic species belonging to Opiliaceae. This edible plant is an important germplasm source with a high economic value in China if propagation were less difficult. Seed dormancy and germination of this species were investigated to improve propagation. Considering seeds have a fully developed embryo and mature and are dispersed in summer, and radicles and epicotyls emerge the following autumn and next spring, respectively, we hypothesized that Y. longistaminea seeds may undergo physiological epicotyl dormancy. Seed moisture content and viability decreased as dehydration occurred. Thus, the seeds may be recalcitrant. The seed germination of this species involves two stages: radicle emergence and epicotyl (shoot) emergence. The optimum temperature was 28 °C and 28 °C/20 °C to radicle emergence. The optimum GA3 solution for the seeds undergoing shoot emergence was 100 mg L-1. The percentages of shoot emergence in seven and 14 days stratification at 5 °C were slightly higher than those in other groups. This study is the first to describe physiological epicotyl dormancy in Y. longistaminea seeds. Under natural conditions, seeds are subjected to Y. longistaminea a autumn → winter → spring temperature. Warm moist conditions and cold stratification can improve radicle emergence and alleviate epicotyl dormancy, respectively. The duration of cold stratification also significantly affects the epicotyl dormancy release of Y. longistaminea. Optimal dormancy breakage methods are warm (28 °C/20 °C) → cold (5 °C) → GA3(100 mg L-1) → warm (28 °C/20 °C).