HIDAYATI1, SITI, N.*, JERRY, M. BASKIN1, AND CAROL, C. BASKIN1, 2. 1School of Biological Sciences, University of Kentucky, Lexington, Kentucky 40506; and 2Department of Agronomy, University of Kentucky, Lexington, Kentucky 40546. - Dormancy-breaking and germination requirements for seeds of Symphoricarpos orbibculatus (Caprifoliaceae).
Fruits (drupes) of Symphoricarpos orbiculatus Moench ripen in
autumn and are dispersed from autumn to spring. Seeds (true seeds +
fibrous endocarp) are dormant at maturity, and they have a small,
linear-shaped embryo that is underdeveloped. In contrast to previous
reports, the endocarp and seed coat of S. orbiculatus are
permeable to water; thus, seeds do not have physical dormancy. No
fresh seeds germinated during 2 wk of incubation over a
15/6-35/20oC range of thermoperiods in either light (14 h
photoperiod) or constant darkness; neither GA3 nor cold
stratification alone overcame dormancy. One hundred percent of the
seeds incubated in a simulated summer --> autumn --> winter --> spring
sequence of temperature regimes germinated, whereas none of those
subjected to a winter --> spring sequence did so. That is, cold
stratification is effective in breaking dormancy only after seeds
first are exposed to a period of warm temperatures. Likewise, embryos
grew at cold temperatures only after seeds were exposed to warm
temperatures. Thus, the seeds of S. orbiculatus have nondeep
complex morphophysiological dormancy. As a result of dispersal
phenology and dormancy-breaking requirements, in nature most seeds
that germinate do so the second spring following maturity; a few may
germinate the third spring. Seeds can germinate to high percentages
under Quercus leaf litter and while buried in soil; they have
little or no potential to form a long-lived seed bank.
Key words: embryo growth, germination phenology, imbibition, morphophysiological seed dormancy, Symphoricarpos orbiculatus, underdeveloped linear embryo.