A quantitative analysis of primary dormancy and dormancy changes during burial in seeds of Brassica napus

<p>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 <i>Brassica napus</i> were tested for primary conditional dormancy (CD). Dormancy changes were quantified through seed population thermal germination parameters to test whether different genotypes of <i>B. napus</i> seeds (<span>944, 966, Alestrom, Danube, Okanto and Rohan</span>) are non-dormant (ND) at the maturity or if they present primary dormancy (D or CD). In a burial experiment, <i>B. napus</i> seeds dormancy cycling in the natural soil seedbank was investigated. Germination of all genotypes decreased at 5 and &gt;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 (<i>T_l(50)</i>) and higher limit (<i>T_h(50)</i>) 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 <i>T_l(50)</i>and <i>T_h(50)</i> 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 <i>B. napus</i> are dormant at dispersal and adopt delayed germination strategies to avoid summer drought. In the burial experiment, the results indicated that<i> B. napus</i> 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.</p>