For plants inhabiting unpredictable environments, scheduling germination can be challenging. Various responses to environmental conditions have been evolved by plants; these responses combine with variation in local climate to construct germination niche. Germination process may be regulated by a number of factors, among them, the type of seed dormancy and dormancy cycling play an important role in promoting survival after dispersal. In the present study, seeds of Brassica napus were tested for primary conditional dormancy (CD). Dormancy changes were quantified through seed population thermal germination parameters to test whether different genotypes of B. napus seeds (944, 966, Alestrom, Danube, Okanto and Rohan) are non-dormant (ND) at the maturity or if they present primary dormancy (D or CD). In a burial experiment, B. napus seeds dormancy cycling in the natural soil seedbank was investigated. Germination of all genotypes decreased at 5 and >20 ^oC, showing narrower breadth of thermal niche for germination. Dormancy-breaking Treatments lead to the widening of thermal range permissive for germination. The lower limit (T_l(50)) and higher limit (T_h(50)) temperatures for germination decreased and increased, respectively, for non-dormant (after-ripened seeds treated with GA₃) seeds compared with fresh seeds in all genotypes. In fresh seeds, the T_l(50) and T_h(50) for various genotypes ranged from 3.61 to 6.5^oC and 25.0 to 29.0^oC, respectively and ranged  from 0.2 to 1.8^oC and 35 to 41.0^oC in non-dormant seeds. Thus, fresh seeds of B. napus are dormant at dispersal and adopt delayed germination strategies to avoid summer drought. In the burial experiment, the results indicated that B. napus must have D/ND cycle in which fresh seeds first become dormant and then the cycle begins (CD → D ↔ CD ↔ ND), thus adopting both risk-prone and risk- adverse strategies to spread the likelihood of survival over time.

Experiment 2 was conducted at the research farm of Aburaihan Campus, University of Tehran, Pakdasht, Iran. Fresh seeds of B. napus (cultivar “Okapi”), which were harvested on 14 June 2017 from farmer’s field at Varamin, Iran, were buried 5 and 30 cm deep in the soil on 23 June 2017. Before burial, the potential of dormancy induction (according to the Hohenheim standard dormancy test (HSDT; Weber et al. 2010) was determined. The potential of dormancy induction is the capability of the responses to seasonal and environmental cues (such as temperature and water potential) that allow seeds to enter (or re-enter) secondary dormancy. The viability of seeds was also determined at the end of HSDT test by crush test (Taab and Andersson 2009; Soltani et al. 2017b). Germination of fresh seeds were tested in distilled water or GA₃ (100 ppm) in the dark.

Researchers who are interested in investigating seed bank can use the data set to realize how to collect data and perform germination trials