Ecophysiology of deep simple epicotyl morphophysiological dormancy in seeds of Gagea lutea (Liliaceae)

The effects of temperature on embryo growth, radicle emergence and cotyledon emergence of Gagea lutea (Liliaceae), a perennial herb widely distributed in Europe, eastern Siberia, the Kurile Islands, Sakhalin and the Far East, were monitored outdoors and in laboratory tests. In Japan, this species inhabits open secondary grasslands and deciduous forests. Seeds with an underdeveloped embryo are dispersed in late May/early June in Hokkaido. The embryo elongates in autumn, and the radicle emerges from the seed in mid-October to mid-November, at temperatures of about 15/4°C. However, cotyledons do not emerge until April, after seeds with an emerged radicle are covered with snow (near 0°C) for about 4 months. In laboratory experiments, temperatures of 25/15°C or 20/10°C followed by 5-10°C were required for embryo growth and radicle emergence. Rate and percentage of cotyledon emergence were promoted by keeping seeds with an emerged radicle under snow. The optimum temperature for cotyledon emergence after 81 d under snow was 15/5°C. Thus, G. lutea has deep simple epicotyl morphophysiological dormancy, and this is the first report of epicotyl dormancy in the genus.