Dormancy-breaking and germination requirements for seeds of Symphoricarposorbiculatus (Caprifoliaceae)

Fruits (drupes) of Symphoricarpos orbiculatus ripen in autumn and are dispe rsed from autumn to spring. Seeds (true seed plus fibrous endocarp) are dor mant at maturity, and they have a small, linear embryo that is underdevelop ed. In contrast it) previous reports, the endocarp and seed coat of S. orbi culatus are permeable to water; thus, seeds do not have physical dormancy. No fresh seeds germinated during 2 wk of incubation over a 15 degrees /6 de grees -35 degrees /20 degreesC range of thermoperiods in light (14-h photop eriod); gibberellic acid and warm or cold stratification alone did not over come dormancy. One hundred percent of the seeds incubated in a simulated su mmer --> autumn --> winter --> spring sequence of temperature regimes germi nated, whereas none of those subjected to a winter --> spring sequence did so. That is, cold stratification is effective in breaking dormancy only aft er seeds first are exposed to a period of warm temperatures. Likewise, embr yos grew at cold temperatures only after seeds were exposed to warm tempera tures. Thus, the seeds of S. orbiculatus have nondeep complex morphophysiol ogical dormancy. As a result of dispersal phenology and dormancy-breaking r equirements, in nature most seeds that germinate do so the second spring fo llowing maturity; a low to moderate percentage of the seeds may germinate t he third spring. Seeds can germinate to high percentages under Quercus leaf litter and while buried in soils they have little or no potential to form a long-lived soil seed bank.