Dormancy-breaking and germination requirements of seeds of four Lonicera species (Caprifoliaceae) with underdeveloped spatulate embryos

Dormancy-breaking requirements and types of dormancy were determined for seeds of Lonicera fragrantissima Lindl. & Part., L. japonica Thunb., L. maackii (Rupr.) Maxim. and L. morrowii A. Gray. Seeds of all four species have underdeveloped spatulate embryos that are about 20-40% fully developed (elongated) when dispersed. Embryos in freshly matured, intact seeds grew better at 25/15 degreesC than at 5 degreesC. Gibberellic acid (GA,) (tested only in the light) was more effective in breaking dormancy in L. maackii and L. morrowii than in L. fragrantissima and L. japonica. Warm- followed by cold stratification was required to break dormancy in seeds of L, fragrantissima, whereas seeds of L. japonica required cold stratification only. Thus, seeds of L. fragrantissima have deep simple morphophysiological dormancy (MPD) and those of L. japonica nondeep simple MPD. About 50% of the seeds of L. maackii required warm- or cold stratification only to come out of dormancy and 50% of those of L. morrowii required warm stratification only, whereas the other 50% did not require stratification to germinate. Thus, about half of the seeds of the two species has nondeep simple MPD, and the other half has morphological dormancy (MD). In these laboratory tests, seeds of L. japonica, L. maackii, and L. morrowii generally germinated to significantly higher percentages in light than in darkness; seeds of L. fragrantissima were not tested in darkness. Peaks of germination for seeds of L. fragrantissima, L. japonica, L. maackii and L. morrowii sown on a soil surface and covered with Quercus leaves under near-natural temperature conditions shortly after seed maturity and dispersal in late June 1997, late November 1997, early November 1996 and late June 1998, respectively, occurred in early March 1998, late February 1998, late March 1997 and early October 1998, respectively. The germination phenologies of seeds of the same species and seed lots buried in soil were similar to those of seeds under leaf litter. High percentages of seeds of all four species germinated both under litter (78-96%) and beneath the soil surface (78-97%). These germination patterns correspond closely with the,requirements for embryo growth and dormancy break in the four Lonicera species.