Impact of Temperature on Seed Dormancy

Seed dormancy is an ecological adaptation that allows seasonal timing of germination for seeds in a population. Several environmental stimuli can trigger dormancy release, the most important being seed moisture content, light and temperature. Of these, temperature is arguably the most important. The objective of this brief review is to consider the various ways temperature impacts seed dormancy release. It will cover general aspects of seed dormancy, temperature effects on primary dormancy and considerations for conducting and interpreting seed dormancy research. Propagators of cultivated plants have long recognized that germination-delaying mechanisms exist in seeds. The first recorded discussion of seed dormancy was written by Theophrastus in 300 B.C. (Evenari, 1981). He recognized that germination of most seeds declined during storage (seed deterioration), while germination in some seeds increased (dormancy release). One problem with discussing seed dormancy is that there is no single recognized terminology to describe the many different types of seed dormancy. Crocker (1916) described seven types of dormancy based on treatments used to overcome them. Subsequently, Nikolaeva (1977) defined dormancy based primarily upon physiological controls. More recently, Lang (1987) proposed the terms eco-, para-, and endo-dormancy to simplify terminology. This system is currently utilized in American Society for Horticultural Science journals. However, this terminology is not sufficient to adequately describe all the types of dormancy found in seeds. Baskin and Baskin (1998) have developed the most complete set of terms to describe seed dormancy. They have extended the dormancy classifications of Nikolaeva to include additional specialty types. In this review, I will use a system based on the work of Nikolaeva, as modified by Baskin and Baskin (Hartmann et al., 2002). It is a classification system that I feel fits both the ecological and horticultural aspects of seed dormancy and is accepted by most of the scientists working in the field of seed biology (Table 1).