ACHENE DORMANCY CHARACTERISTICS OF THREE ROSE SPECIES AND THE METHODS FOR IMPROVING GERMINATION

Roses are a group of world famous garden plants, and strong dormancy exists in the achenes. We characterized the water absorption of achenes, the inhibition of extracts of pulp and achenes, effects of different pretreatments on breaking dormancy to determine the dormancy type and mechanism. Achenes of three rose species had physiological dormancy (PD) based on the water-permeable seed coat and fully developed embryo. Rosa rubus had intermeditate PD, and Rosa longicuspis and Rosa helenae had deep PD. The best treatment for improving germination was warm plus cold stratification, as indicated by higher germination percentage (GP) and lower moldy achene percentage for R. rubus (74.9 +/- 2.1%) and R. longicuspis (25.9 +/- 2.1%). For R. helenae, GP (36.3 +/- 1.5%) was highest treated by H2SO4 scarification followed by warm stratification at 25 degrees C for eight weeks and cold stratification at 5 degrees C for sixteen weeks. Prolonged period of cold stratification significantly increased germination speed and moldy achene percentage especially when combined with H2SO4 scarification. The physiological dormancy of rose achenes was caused jointly by inhibitory substances in pulp and achenes, mechanical barrier of thick pericarp and physiological dormancy in embryo.