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

Abstract

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°C, showing narrower breadth of thermal niche for germination. Dormancy‐breaking treatments lead to the widening of thermal range permissive for germination. The lower limit (Tl(50)) and higher limit (Th(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 Tl(50) and Th(50) for various genotypes ranged from 3.61 to 6.5°C and 25.0 to 29.0°C, respectively and ranged from 0.2 to 1.8°C and 35 to 41.0°C 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.

The seed germination spectrum of 528 plant species: a global meta-regression in relation to temperature and water potential

“…The traits considered in this study included cardinal temperatures (T b , T opt and T max, which are estimated through regression procedure), thermal time required for germination (θ 50 , which is calculated via θ sub (g) = ( T - T b ) t g and θ sup ( g ) = ( T c - T ) t g ), and base water potential ( b Ψwhich is quantified by and . For further information, see Garcia-Huidobro et al ., (1982), Gummerson (1986), Dahal & Bradford (1994) and Maleki et al (2021), and references therein. For literature mining, seven categories of plant species were defined as previously (Dürr et al ., 2015): crops, horticultural species (vegetables, leafy vegetables, ornamentals and medicinal plants), forage and rangeland species, Cactaceae and Agavaceae, wild species (invasive, endangered, wild potential medicinal plants), tropical trees and other trees.…”

“…Estimates of T b are also valuable in calculating thermal times for the completion of germination in the sub-optimal range between the T opt and T b . As thermal time varies with sub-populations/percentiles, such estimates represent a powerful means for predicting germination efficiency amongst a seed population under any, including changing, environmental conditions (Gummerson, 1986; Dahal & Bradford, 1994; Finch-Savage et al ., 2005; Maleki et al ., 2021). This concept of the thermal parameters of germination can be expanded by incorporating different water potentials, leading to hydrotime and hydrothermal time models describing the seed response above a base water potential for germination (b) and its interaction with temperature, respectively (Gummerson, 1986; Dahal & Bradford, 1994; Finch-Savage et al ., 2005; Donohue et al ., 2010; Bewley et al ., 2012)…”

“…Estimates of thermal times, cardinal temperatures (i. e. T b , T opt and T max ) and b have been quantified for many species, allowing an interpretation of seed germination within different environments (Trudgill et al ., 2005; Orrù et al ., 2012; Dürr et al ., 2015; Seal et al ., 2017; Zhang et al ., 2020; Maleki et al ., 2021) as well as intra- and inter-species comparisons facilitating prediction of their spatial distribution (Dürr et al ., 2015). How crop and weed establishment occur under current and future climates (Forcella et al ., 2000; Dürr et al ., 2001; Gardarin et al ., 2012; Lamichhane et al ., 2020, 2022) and how plants synchronize germination and subsequent seedling growth with favorable conditions can be interpreted quantitatively (Dürr et al ., 2015; Gremer et al ., 2020a; Maleki et al ., 2021). Application of these approaches for agricultural and ecological purposes has proven to be useful for an increased understanding of crop diversification in space (intercropping, relay cropping) and time (e.g.…”

“…How trait– environment interactions can shape the germination response through the thermal niche has been comprehensively modelled in the laboratory (Thompson & Ceriani, 2003; Catelotti et al ., 2020) and in situ (Porceddu et al ., 2013; Blandino et al ., 2022). Thermal time models in combination with relevant environmental parameters have been widely used to investigate thermal niche and germination responses to accumulated temperature in agricultural and more natural settings (Garcia-Huidobro et al ., 1982b; Covell et al ., 1986; Pritchard & KR., 1990; Hardegree, 2006; Porceddu et al ., 2013; Dantas et al ., 2020; Maleki et al ., 2021). Previous studies have shown that variation in threshold-type responses to ongoing environmental conditions among species may reflect the seeds’ thermal memory of the maternal environment (Fernández-Pascual et al ., 2019), as evidenced by the cumulative thermal effects on seed development (Daws et al ., 2004; Baskin & Baskin, 2014) and varying levels of seed dormancy (Pritchard et al ., 1999; Porceddu et al ., 2013).…”

An Overview of Environmental Cues That Affect Germination of Nondormant Seeds

“…The temperature(s) at which germination occur(s) at its maximum rate and percentage is the optimum temperature(s). Some seeds with nondeep PD have been shown to germinate over a narrow range of temperatures when their degree of dormancy is high, and they germinate over a broader range of temperatures as dormancy is broken [4][5][6]. For nondormant seeds, the temperature window for germination corresponds to the cardinal temperatures.…”