Invited Review: Mimicking the natural thermal environments experienced by seeds to break physiological dormancy to enhance seed testing and seedling production

Physiological dormancy (PD) is the most common class of seed dormancy on earth. It is highly variable and is an important part of the adaptation of many species to their habitat. Often, two questions are asked about seeds that failed to germinate in a germination test: (1) are they non-viable or dormant, and (2) if dormant do they have PD and how is it broken? We provide an overview on how to approach studies of species with PD for which few or no data are available. Information about habitat environmental conditions during the seed stage can be used to formulate hypotheses on dormancy-breaking and germination requirements. These hypotheses can be tested by a move-along experiment. There are three levels of PD, and they are distinguished by the conditions required to break PD and promote germination. Seeds with non-deep PD (the most common level of PD) require different conditions for dormancy-break and germination, i.e. a change in the season, while those with intermediate and deep PD germinate at the dormancy-breaking conditions, e.g. during a long period of cold stratification. Knowing how to break PD enhances testing for seed viability and helps ensure high germination percentages of viable seeds.