Abstract
Rosa rugosa Thunb. has been explored multi-function in medicinal, edible, cosmetic, ornamental and ecological etc. However, R. rugosa natural populations have recently declined substantially in China, besides of global climate change, this species also has the defect of limiting the reproduction of itself such as the hard-to-release seed dormancy. In this study, only 30% of R. rugosa seeds were viable, and the others were incompletely developed or diseased seeds. Without stratification, morphologically complete viable seeds imbibed water but those seeds could not germinate even after seed husk removal under suitable condition to exhibit a physiological dormancy. After cold (4°C) and warm (18 ± 2°C) stratification, macromolecular substances containing carbon or nitrogen accumulated, and respiration, antioxidant enzyme activity, and gibberellin (GA3) /abscisic acid (ABA) and auxin (IAA)/ABA ratios increased significantly in seeds. Water absorption also increased as endocarps softened. Thus, physiological dormancy of seed was broken. Although warm and cold stratification increased separation between endocarp and embryo, the endocarp binding force was removed insufficiently, because only 10.20% of seeds germinated. Therefore, stratified seeds were treated with simulated bird digestion. Then, folds and cracks in loosened endocarps increased permeability, and water absorption rate increased to 64.43% compare to 21.14% in cold and warm stratification treatment. With simulated digestion, 24.20% of radicles broke through the endocarp with plumules and cambiums to develop into seedlings. Thus, the seed dormancy type of R. rugosa is physiological as seeds imbibed water and possessed fully developed embryos with a low growth potential in combination with a mechanical constraint from the endocarp. Cold stratification helped remove physiological dormancy, and additional warm stratification accelerated the process. The optimal stratification treatment was 4°C for 45 days followed by 18 ± 2°C for 15 days. After warm and cold stratification, simulated bird digestion broke the mechanical constraint from the seed covering layers. Based on this research, production of R. rugosa seedlings can be greatly increased to help protect the species from further declines.
Highlights
Rosa rugosa Thunb. from Rosaceae is a perennial ornamental shrub originally from east Asia (Yu et al, 1985)
Among the randomly selected seeds, TCC dyed 30% seed embryos light red (Figure 1D) and considered active (Figure 1E), the other seeds were too small, diseased to dark brown or the embryos are not fully developed (Figure 1F) even embryoless. These actively fresh embryos failed to germinate even under suitable conditions. These results indicated that R. rugosa seeds entered a physiological dormancy with hard-to-break endocarp after fruit maturity
A species invests in longlived individuals to help populations persist through periods of unfavorable conditions (Lennon et al, 2021)
Summary
Rosa rugosa Thunb. from Rosaceae is a perennial ornamental shrub originally from east Asia (Yu et al, 1985). R. rugosa natural populations are generally distributed in dunes, where they have an essential role in maintaining coastal ecology (Qin et al, 1994). In northern Europe, R. rugosa is most likely one of the most frequent invasive plant species in natural and seminatural habitats (Jan et al, 2009). Growth and reproductive traits of populations of invasive R. rugosa from China are significantly better than those of native populations in coastal dunes of northwest Europe (Zhang et al, 2018). In China, natural R. rugosa populations have decreased sharply from year to year, and the species is only distributed at the Tumen River in Jilin Province, on the southern coast of Liaoning Province, and on the eastern coast of Shandong Province (Li and Zhang, 2007). Growth of roses has improved, but how to expand and renew populations remains to be determined
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