Overview of seed dormancy in Viburnum (Caprifoliaceae)

Many species of Viburnum are cultivated ornamentals, but their propagation from seeds may require many months. This overview provides a better understanding of why germination may take so long. Seeds have a linear underdeveloped embryo which must grow inside the seed before the root emerges. In addition, the embryo has physiological dormancy (PD); thus, seeds have morphophysiological dormancy (MPD). In most species of Viburnum, there is a period of several weeks or months between root and shoot emergence, and this kind of dormancy is described as deep simple epicotyl MPD. Warm stratification (summer) is required to break part of the PD, after which the embryo grows and the root emerges (autumn). Then, the seed with the developing root must be cold-stratified to break the remaining PD in the shoot, which emerges in spring. An analysis of the dormancy-breaking and germination requirements of seeds with deep simple epicotyl MPD reveals that only the shoot has this level of MPD; the root has nondeep simple MPD and thus requires only warm stratification to break the PD and promote growth of the embryo. In at least a few species of Viburnum, the shoot has only nondeep simple MPD, and dormancy in seeds of these species is described as nondeep simple epicotyl MPD. We discuss use of the " move-along" experiment to help define the seed dormancy-breaking and germination requirements of a species and present data for V. formosanum, which has nondeep simple epicotyl MPD. Clearly, if cold stratification is given first, in this and other species of Viburnum, i.e., seeds are sown in early winter, germination is delayed because breaking of the first part of PD (by warm stratification) cannot occur until summer.