D.P. de Vries, L.A.M. Dubois
The smooth germination of mature Hybrid rose achenes is hampered by (i) hardseededness (HS), (ii) primary dormancy (PD) and (iii) germination polymorphism (GP). HS is owing to the hard pericarp. PD is, in principle, a natural phenomenon that protects the seeds from precocious germination. For germination, PD must be lifted by after-ripening. When the process of after-ripening is interrupted seeds become secondary dormant (SD). When SD both seeds and naked embryos are highly recalcitrant to germination. After-ripening of Hybrid rose seeds consists of two steps (i) softening the pericarp, (ii) hydrolysing and/or antagonizing the inhibitor ABA, present in the testa and/or embryo. The ratio ABA:GA (present or newly synthesized) controls readiness for germination. Imbibing previously cold-stratified Hybrid seeds in GA3, enhanced the even emergence and germination percentage. Likely owing to their unique descent, Hybrid roses bear achenes that are less recalcitrant to breaking PD than those of many rose species. Different levels of PD, occurring between the rose species, can be traced back to adaptation to their natural habitat. Comparing the after-ripening requirements of Hybrid seeds with those of rose species is a false position. GP is caused by varying temperatures during fruit ripening, is promoted by prolonged pollination periods, effects variation in dormancy and as such contributes to uneven germination of Hybrid seeds. PD of Hybrid seeds is deeper as mean ambient temperatures during the last 30 days of fruit ripening were lower. Hence, lower temperatures in autumn, as commonly set in glasshouses, cause deeper PD. Rose seeds may germinate without any after-ripening when harvested unripe. Each year, breeders should compose the “best protocol” for cold stratification/germination of Hybrid rose seeds from the elements: (i) the period of pollination, (ii) the temperatures during 30 days prior to hip ripening, (iii) the storage of achenes between extraction from the hip and sowing, (iv) the intended warm period prior to stratification and (v) the temperatures set for stratification.
de Vries, D.P. and Dubois, L.A.M. (2015). FACTORS AFFECTING THE GERMINATION OF HYBRID ROSE ACHENES: A REVIEW. Acta Hortic. 1064, 151-164
DOI: 10.17660/ActaHortic.2015.1064.18
abscisic acid, achene, after-ripening, cold stratification, embryo, hardseededness, seed polymorphism, primary dormancy, secondary dormancy, Rosa

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