Studies On Distant Cross-breeding And Embryo In Vitro Culture And Somatic Embryogenesis In Tree Peonies

Distant cross-breeding of tree peony is the main means of cultivar improvement at present and for quite a long time in the future, however, long breeding period and cross abortion are the two main obstacles for obtaining new cultivars effectively. The use of some assistant methods such as ovule, embryo and embryoid (somatic embryo) in vitro culture will be very important for an effective program in peony breeding. In this thesis, distant crosses of peonies, the cross abortion and the assistant methods presented above were systematically observed and studied by investigation and crossing in the field, and light microscopy and culture in vitro in the lab. Some intersectional hybrid seedlings were firstly obtained in China and the main reason resulting in cross abortion in most combinations was confirmed. A protocol for embryo in vitro culture was established and somatic embryos were firstly induced in the world from which plantlets were successfully regenerated in tree peonies. The main results were as follows:1.The main reason for low seed-set in distant cross-combinations of peonies was the barrier of fertilization, and the key factor influencing on seed-set was the cross-combination. The herbaceous peony seedlings 1~#×' L'Esperance' (Paeonia delavayi var.lutea×P.×suffruticasa)or ' Golden Era' ('Golden Isles'(P. delavayi var.lutea×P.×suffruticasa)XMi\ed pollen) or'Souvenir de Maxime Cornu' (P. delavayi var.lutea×P.×suffruticasa) were better cross-combinations, and the seedlingsl~# was a good parent plant with better compatibility in all intersectional crosses. Pollen viability and seed-set ratio of P.rockii'Shu Sheng Peng Mo' and 'Zi Die Ying Feng' and P.ostii'Feng Dan Bai' were both rather high, however, castration should be in time to avoid autogamy when used them as female parents. The main reasons for the sexual reproduction abortion in 'High Noon'(P.delavayi var.lutea×P.×suffruticasa) were that it can't form enough viable gametes and lack valid pollination. 787 flowers were pollinated in 31 cross combinations with 422 seeds obtained, 54 young seedlings were planted after 4 years' research work (2002～2005) . Thereinto, the results of firstly gained 412 seeds and 10 Itoh hybrid seedlings of 3-year-old from 6 intersectional cross- combinations, indicated that intersectional cross-breeding which was immense potential has started in China.2.The better sterilization method was that ovule was directly surface-sterilized with 70%(v/v) ethanol for 30～60s and with 0.1%(w/v) aqueous mercuric chloride solution for 6min, respectively followed by three rinses with sterile distilled water. Young ovule before 48 days after anthesis (d.a.a.) failed to be cultured and the ovule in which embryo completed organogenesis was cultured to plantlet.