Abstract
Cold stratification is a requirement for seed dormancy breaking in many species, and thus it is one of the important factors for the regulation of timing of germination. However, few studies have examined the influence of various environmental conditions during cold stratification on subsequent germination, and no study has compared such effects on the performance of dormant versus non-dormant seeds. Seeds of halophytes in the cold desert might experience different light and salinity conditions during and after cold stratification. As such, dimorphic seeds (non-dormant brown seeds and black seeds with non-deep physiological dormancy) of Suaeda aralocaspica were cold stratified under different light (12 h light–12 h darkness photoperiod or continuous darkness) or salinity (0, 200 or 1,000 mmol L-1 NaCl) conditions for 20 or 40 days. Then stratified seeds were incubated under different light or salinity conditions at daily (12/12 h) temperature regime of 10:25 °C for 20 days. For brown seeds, cold stratification was also part of the germination period. In contrast, almost no black seeds germinated during cold stratification. The longer the cold stratification, the better the subsequent germination of black seeds, regardless of light or salinity conditions. Light did not influence germination of brown seeds. Germination of cold-stratified black seeds was inhibited by darkness, especially when they were stratified in darkness. With an increase in salinity at the stage of cold stratification or germination, germination percentages of both seed morphs decreased. Combinational pre-treatments of cold stratification and salinity did not increase salt tolerance of dimorphic seeds in germination phase. Thus, light and salinity conditions during cold stratification partly interact with these conditions during germination stage and differentially affect germination of dimorphic seeds of S. aralocaspica.
Highlights
Seed germination is a critical stage in the life cycle of higher plants, especially for annuals (Gutterman, 1993; Gutterman, 2002)
Baskin & Baskin (1977) reported that after one week of stratification, germination percentage of Asclepias syriaca was highest for seeds cold stratified in light incubated in darkness and germination was lowest for seeds stratified in darkness and incubated in light after
Effect of light during cold stratification and incubation stage on germination Germination percentage of brown seeds during cold stratification was significantly affected by stratification time (P = 0.018) but not by light condition during cold stratification (P = 0.189) (Table 1)
Summary
Seed germination is a critical stage in the life cycle of higher plants, especially for annuals (Gutterman, 1993; Gutterman, 2002). Known as pre-chilling treatment, is widely used to improve synchronization of germination It is a requirement of dormancy breaking for seeds possessing physiological dormancy in regions with a cold winter (Baskin & Baskin, 2014). Few studies have tested effects of different environmental conditions during cold stratification on dormancy breaking and their interaction with conditions during subsequent germination stage (Baskin & Baskin, 1977; Walck, Baskin & Baskin, 1997; Wang et al, 2011). Redondo-Gómez et al (2011) present evidence that, compared with seed germination under different salinity directly, the combinational pre-treatments of cold stratification and salinity decrease germination percentage. Heretofore, no study has compared germination responses of dormant and non-dormant seed morphs of a seed-heteromophic species to different environmental conditions during cold stratification
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