Studies On The Reproductive Biology Of Alnus Rubra

Red alder (Alnus rubra) has broad application prospects and commercial values, it has been successfully introducted to Jiangsu Province and its surrounding areas in China. In this paper, we observed and measured pollen morphology, pollen viability and storage characteristics of red alder based the material from Luhe, Nanjing. The whole process of sexual reproduction e.g. differentiation of flower buds, formation of male and female gametophytes, double fertilization and embryonic development, were also comprehensively studied. We expect to provide a theoretical basis for breeding practice of Alnus and further promote of red alder and also accumulate data for pollen and embryo studies of Betulaceae. The main conclusions are as follows:(1) The pollen of red alder belongs to birch-type with clear apertures and mostly 4-5 inaperturate, there were belt thickening between inaperturates. Red alder had a wide range of ecological adaptation, so it is feasible to spread it in large area of china.(2) Pollen viabilities of red alder were tested by TTC staining and in vitro culture methods. The effects of different storage methods and different thawed temperatures on the germination of pollen were also investigated. The results showed that TTC method was not suitable for determination of red alder pollen; The rate of pollen germinate reached the highest after incubated for 8h on the media supplemented with 10% sucrose and 0.1% boric acid. Pollen viability decreased with the extension of storage time. The-20℃was a better temperature for red alder pollen storage. Through tap water was the best method for pollen thawed in cryopreservation, but pollen storage time was not extended under cryopreservation condition.(3) Female and male inflorescences were amentiferous. Each cymelet had one primary bract, two secondary bracts and two tertiary bracts. The two secondary bracts developed earlier than the two tertiary ones, all were originated from cymelet primordia. Female and male flowers developmental process showed a lack of synchronization, and pollination and fertilization interval was about two months.(4)Embryonic characteristics:glandular tapetum, anatropous ovules, single integument, thick nucellar, linear or "T"-type megaspore tetrad, polygonum-type embryo sac, nuclear-type endosperm, multiple archesporia and eventually developed into a embryo sac, a very few with two embryo sacs, chalazal end as the functional megaspore.(5) The low rates of seed sets in red alder may be caused by pollen abortion, embryo sac abortion and embryo sac shrinkage occurring in the process of embryogenesis.