Abstract: 【Objective】 The aim of this study is to reveal the reasons for barriers of interspecific hybridization between R. rugosa and R. hybrid. It is meaningful to improve the theory and techniques of breeding ornamental R. rugosa. 【Method】 A wild R. rugosa from Muping, a cultivar of R. rugosa ‘Tanghong’ , two cultivars of R. hybrid ‘Salvia’ and ‘Red Cap’ were used as plant materials. The fruit setting rate, seed number per fruit, seed length, percentage of seeds with embryo, germination rate of seeds with embryo and survived seedling rate of interspecific hybridization (MPבSalvia’, MPבRed Cap’) and intervarietal hybridization (MPבTanghong’) were investigated. The growth of pollen tubes in the styles was observed with fluorescent microscope, Fertilization and development of embryos were observed by conventional paraffin sectioning. 【Result】 The fruit setting rate and seed number per fruit of MPבSalvia’ were significantly lower than those of intervarietal hybridization. No seed was obtained from MP בRed Cap’. The seeds of MPבSalvia’ were of uneven size. The length of 76.67% of small seeds with no embryo and endosperm was simply (0.24±0.07) cm, these small seeds could not germinate. The length of 23.33% of big seeds with embryo and endosperm was (0.61±0.05) cm. But the germination rate and survived seedling rate of these big seeds were significantly lower than those of intervarietal hybridization. Two hours after pollination, the pollens of interspecific hybridization and intervarietal hybridization both germinated on the chapiters, but a great deal of callose deposited at the apex of pollen tubes of interspecific hybridization. Twenty to twenty-four hours after pollination, pollen tubes of intervarietal hybridization grew into ovary, but all the pollen tubes of MPבRed Cap’ and most of the pollen tubes of MPבSalvia’ were arrested at the middle of the styles. Little callose accumulated in the canal cells and spaces of the style of intervarietal hybridization, but a great deal of callose accumulated in the canal cells and spaces of the style of interspecific hybridization. A few pollen tubes of MPבSalvia’ grew into the ovary and fertilization was accomplished. But 79.42% of the embryos of interspecific hybridization aborted at the stage of heart-shaped embryo which formed on the 15th day after pollination, and 20.58% of the embryos of interspecific hybridization continued to develop.【Conclusion】The barriers of MP בRed Cap’ happened before fertilization, and the dual barriers of MP בSalvia’ happened before and after fertilization. The pre-fertilization barriers were caused by the pollen tubes stopping growth at the middle of the styles which may be connected with excessive callose accumulating at the apexes of the pollen tubes and in the canal cells and spaces of the styles. The post-fertilization barriers was due to hybrid embryo abortion at the stage of heart-shaped embryo.

Key words: Rosa rugosa , R. hybrid , interspecific hybridization , pollen tube , callose