Study On Inducing Technology Of Populus Davidiana Dode

Populus davidiana Dode is a native tree species which is widely distributed in China, and it is one of the most important trees of white poplars. It can adapt in northern cold, drought and infertile soil. It is the high-quality industrial material which its material quality is quite well, its wood is light, soft and homogeneous and its wood-color is light white. Breeding triploid of Populus davidiana Dode can alleviate the imbalance between supply and demand of papermaking materials. Choosing Populus davidiana Dode and its hybrids as the subject, the gametogenesis and development of megagamete, pollen mother cells and embryo sac of Populus davidiana Dode were studied to find out the best treatment conditions and cytology mechanism of induction triploid with colchicine before and after pollination, the results showed as follows:1. The meiosis of microgamete of Populus davidiana Dode showed a high correlation to external characters of male flower buds, the color of anther gradually deepened from peak green into deep red. Populus davidiana Dode cultured in water in the greenhouse for40h, microsporogenesis has started split into leptotene. And when the color of anther was red, it developed to the tetrad about108h. When cultured in water for116h, meiosis stages of male gametophyte developed into mononuclear and binuclear pollen stage. There were about160h to complete the microspore and male gametophyte development.2. The meiosis of the megaspore mother cells of Populus davidiana Dode showed a high correlation to external characters of female flowers buds. Female flowers gradually exposed bud scales and elongated with meiosis. Around84h after hydroponic, there was the beginning of meiotic prophase I-leptotene stage, the catkin emerged from bract scales slightly at this time.At112h, flower buds began to enlarge, one fourth of the catkin protruded from the bract scales in late leptotene. When cultured136h, one third of the catkin emerged from the bract scales, and the meiosis was pachynema; cultured for160h, female flowers buds elongated obviously, reveal1/2inflorescence and the meiosis developed into Metaphase I. Exposing two-thirds of inflorescence, the meiosis developed from the anaphase I into Metaphase II at180h. After192h, stigma significantly exposed, and stage was anaphase II to tetrad.3. The meiosis stages of megaspore and microspore had close correlation during their development. According to the corresponding correlation between male gamete and male gametes, the meiosis stage of megaspore could be determined through pollen mother cells in the same environmental condition. When the meiosis of megaspore mother cell reached leptone, microspore mother cell had developed Anaphase I into Anaphase Ⅱ.When male gametophyte reached to tetrad and mononuclear, the megaspore arrived at bouquet stage. While male gametophyte developed into mononuclear aside, megasporocyte meiosis was pachytene; while male gametophyte developed of binuclear, megasporocyte continued to split from the lane until the completion of meiosis.4. The embryo sac of Populus davidiana Dode is polygonum type. At18h after pollination,one nucleate embryo sac formed. At36h after pollination, the nucleate separated into two new nucleus formed two-nucleate embryo sac. Over12h two-nucleate embryo sac developed into four-nucleate embry sac. A mature embryo sac would come into being in72h. The stigma of the optimal receptivity stage of Populus davidiana Dode was3d.The optimal pollination period was that the red stigma lobed at180°and excreted a great deal of mucilage at216h after pollination.5. Research showed that induction with colchicine before and after pollination were effective way to get the Populus davidiana Dode triploid. Mechanism of before pollination was the induction its megaspore mother cell chromosome doubling, and the effective induced period was leptotene and bouquet stage, the optimum concentration was0.3%, the most appropriate treatment duration was24h and obtained8triploid with induction rate16%. After pollination treatment triploid mechanism was the embryo sac chromosome doubling. Induction of chromosome doubling of embryo sac was effective condition48～72h after pollination with0.3%colchicine solution for24h, with induction rate19.2%. Two years experiments for embryo sac chromosome doubling get24triploid.6. There were significant variations in leaf morphology, stomata features, height, diameter at ground, chlorophyll content between two-year-old triploids and diploids. Whether the characters of two-year-old seedling is stable or not, it remains to be seen.