Seed and Embryo Germination in Syringa vulgaris and S. reflexa as Affected by Temperature during Seed Development

Effects of controlled temperature conditions during seed development on seed and embryo germination of Syringa vulgaris were studied using vegetatively propagated mother plants. Seeds from mother plants grown at 18–24°C were partially dormant at low (15°C) but not at high (21°C) germination temperature, while seeds from outdoors or from plants grown at 12°C were not dormant at all. Seed dormancy at low temperatures was induced as well when branches from outdoor plants were kept at 18–24°C for the last two‐three weeks before harvesting. The dormancy induced by 24°C during seed development was not broken by keeping branches at 12°C for the last two‐three weeks. In most cases the induced seed dormancy was broken completely by gibberellic acid. Embryo germination at 24 or 15°C was not affected by mother plant temperature. Part of the embryos from plants grown at 24°C were, however, dormant at 9°C. The ability of embryos to germinate in osmoticum was only slightly affected by mother plant temperature. The mechanical resistance of the endosperm was significantly higher in the seeds from plants grown at 24°C than in seeds from 12°C. Both the embryos and the seeds of S. reflexa were dormant at the time of termination of embryo elongation. Experiments with three seed‐propagated mother plants indicated that the water potential of embryos may be reduced by high mother plant temperature.