Deep Simple Morphophysiological Dormancy in Seeds of Epimedium koreanum Nakai native to Korea

The Berberidaceae is a family reported to have morphological dormancy (MD) or morphophysiological dormancy (MPD) with underdeveloped embryos. There are few reports on seed dormancy and germination in Epimedium koreanum Nakai. This research was performed to determine the type of dormancy for seeds of E. koreanum and its dormancy-breaking requirements. Seeds were collected on 5 June 2015 from plants growing in the Korea National Arboretum. Phenology of embryo growth, germination, and seedling emergence in field condition was observed. The effects of temperature sequences and GA₃ treatment on dormancy break and germination were evaluated. Seeds had underdeveloped embryos that were below 10% of the length of fully matured seeds. In phenology study, the embryos grew very little from June to early September, while rapid growth of the embryos was observed from late September to late November. Embryo growth was completed from late November until early December. Seeds sown on the field soil started to germinate from February, and most seedlings were observed on late March. In laboratory experiments, embryos grew rapidly when the seeds were moved from 25/15℃ to 15/6℃. However, the embryos in constant temperatures (25℃) grew very little. Most of the seeds germinated in only warm followed by cold temperature sequence. Therefore, it seems that warm followed by cold temperature sequence is essential for dormancy break and germination in the seeds. GA₃ treatment increased embryo growth in the seeds, but none of them germinated at 20℃. Based on these results, seed dormancy of E. koreanum can be broken through warm followed by cold temperature sequence and classified as having deep simple morphophysiological dormancy (MPD)