Combinational dormancy in seeds of Sicyos angulatus (Cucurbitaceae, tribe Sicyeae)

Seeds with a water-impermeable seed coat and a physiologically dormant embryo are classified as having combinational dormancy. Seeds of Sicyos angulatus (burcucumber) have been clearly shown to have a water-impermeable seed coat (physical dormancy [PY]). The primary aim of the present study was to confirm (or not) that physiological dormancy (PD) is also present in seeds of S.angulatus. The highest germination of scarified fresh (38%) and 3-month dry-stored (36%) seeds occurred at 35/20°C. The rate (speed) of germination was faster in scarified dry-stored seeds than in scarified fresh seeds. Removal of the seed coat, but leaving the membrane surrounding the embryo intact, increased germination of both fresh and dry-stored seeds to >85% at 35/20°C. Germination (80-100%) of excised embryos (both seed coat and membrane removed) occurred at 15/6, 25/15 and 35/20°C and reached 95-100% after 4 days of incubation at 25/15 and 35/20°C. Dry storage (after-ripening) caused an increase in the germination percentage of scarified and of decoated seeds at 25/15°C and in both germination percentage and rate of excised embryos at 15/6°C. Eight weeks of cold stratification resulted in a significant increase in the germination of scarified seeds at 25/15 and 35/20°C and of decoated seeds at 15/6 and 25/15°C. Based on the results of our study and on information reported in the literature, we conclude that seeds of S.angulatus not only have PY, but also non-deep PD, that is, combinational dormancy (PY+PD).