*3.2.1 Primary dormancy*

Primary dormancy is induced during the seed maturation phase and reaches a high level in freshly harvested seeds, meaning seeds with primary dormancy are dispersed from the mother plant in a dormant state [1]. During subsequent dry storage of seeds (after-ripening), dormancy slowly reduces [65]. Primary dormancy is maintained by the accumulation of abscisic acid (ABA) during seed maturation to prevent viviparity [66] and requires a period of after-ripening before seeds have the capacity to germinate under favorable conditions. The level of primary dormancy in seeds is determined by several factors of genetic and non-genetic origin [67]. All these factors may cause physiological variability which is matched with differences in seed morphology (size, weight, color etc.) or simply heterogeneity in degree of dormancy [5]. Developing seeds rarely germinate, and when precocious germination does occur, it is frequently associated with deficiencies in ABA synthesis or sensitivity [2]. The induction of primary dormancy is linked to the two peaks of ABA accumulation during developmental phases of seeds. As observed in studies carried out on Arabidopsis, the first ABA peak occurs prior to embryo maturation hence it's described as maternal. The second peak regulated by the genome of the embryo is observed during maturation hence described as embryonic ABA peak. The accumulation of embryonic ABA, but not maternal ABA, is indispensable for the induction of primary dormancy [68].

Primary dormancy has the advantage of guaranteeing complete development of embryo, and prevents precocious germination in species like maize. Once seeds acquire primary dormancy during late maturation its water content decreases drastically. It is the case with some *Arabidopsis* accession Cvi, in which water content decreased by almost 5-fold was noticed after acquiring primary dormancy to late maturation phase [69]. When the moisture content is further reduced to a certain level by dry storage, the seed loses primary dormancy. This process of breaking primary dormancy includes a decrease in ABA concentration and sensitivity, an increase in GA and light sensitivity, and a widening of temperature range for seed germination [70].
