Whole-seed development in Sicyos angulatus (Cucurbitaceae, Sicyeae) and a comparison with the development of water-impermeable seeds in five other families

Sicyos is the only member of the Cucurbitaceae known to have water-impermeable seeds, that is, physical dormancy (PY), and development of seeds with PY has not been studied in detail in this family. Our primary aim was to describe seed development in Sicyos angulatus from pollination to seed maturity and to compare it with the development of water-impermeable seeds in other families reported in the literature. Full seed stage (highest moisture content [MC]) occurred 4-6 days after pollination (DAP) and physiological maturity occurred 20 DAP. Seeds became water impermeable 32 DAP, with 14.6% MC. The hilum was the site of water loss during the final stage of maturation drying. Excised embryos could germinate from 20 DAP to 36 DAP, whereas no intact seeds germinated during any stage of seed development. Mechanical scarification did not promote germination of seeds after the seed coat became water impermeable at 32-36 DAP. Based on a previous study of seed dormancy and germination in S. angulatus, we suggest that germination in these scarified seeds may have been prevented by resistance of inner membrane and fruit-seed coat to embryo expansion. The MC when seeds became impermeable (14.6%) is in the range of that reported for seeds of species in five other families with PY. Information on seed development in S. angulatus will be useful in planning the timing of management strategies for this pernicious annual weed.