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Five kinds (classes) of seed dormancy are known: physiological (PD), morphological (MD), morphophysiological (MPD), physical (PY), and combinational (PY+PD). PD is the most common class in the major vegetation zones of the world followed by PY, MPD, MD, and (PY+PD). Each class is described, and a dichotomous key to identify them is presented. The environmental conditions required to break PD, MD, MPD, PY, and (PY + PD) and promote germination are discussed. To help determine which treatments to use for breaking dormancy in seeds with water-permeable seedcoats (PD, MD, MPD), a “move-along experiment” is recommended. Little or no convincing evidence for the role of microbes or mechanical abrasion by soil particles in breaking PY can be found in the literature. However, there is good evidence that the water plug or gap in the seed or fruit coat of seeds with PY responds to environmental cues that permit timing of imbibition and germination to be well controlled in nature. Seeds of many species remain viable after passing through the digestive tracts of animals, with varying effects on germination.
Pomegranate is an important fruit crop cultivated in many countries, and development of new cultivars depends on the plant breeders being able to produce plants from seeds. Poor quality and low yield of cultivars are widespread problems that greatly restrict development of the pomegranate industry. Our purpose was to gain a better understanding of the seed dormancy-breaking and germination requirements of four cultivars of pomegranate from Xinjiang Province, China, which would be useful in improving old cultivars and developing new ones. Fresh pomegranate seeds incubated on moist filter paper imbibed water, but they germinated to only 16% to 20%. Sulfuric acid scarification, cold stratification, and warm followed by cold stratification significantly increased germination percentages. Seeds soaked in concentrated H2SO4 for 40 minutes followed by cold stratification for 2 months germinated to 65%, and those warm stratified for 1–3 months followed by cold stratification for 2 months germinated to 75% to 80%. Seeds of pomegranate have nondeep physiological dormancy (PD).