| Xinjiang Wild Apple (Malus sieveisii) exists abundant genetic diversity, which possesses the great potential of further exploitation and utilization as a good fruit breeding material. Its one-year-old stem segment were selected as the experimental material in this study on the tissue culture, cryopreservation by vitrification and changes of morphological characteristics. Its genetic stability was proved in this study. And some factors affecting cryopreservation by vitrification as well as its genetic variation marked by SSR were also investigated and analysed. The aim of this study was to provide references for the Cryopreservation of Northern Fruits, and provide the technical support for the conservation on M. sieversii.The main results were as follows:1.Experiment was carried out on browning control of stem segmane explant of M. sieversii. An assessment standard was made for browning grades. Some factors which would affect browning rate were investigated, including active carbon, antiscorbutic vitamin, phytic acid, illumination,etc.The results showed us the bad effect of factors mentioned and dark culture for browning control on primary culture of explant of M. sieversii, while the continuous transfer was much better.2. Medium for M.sieversii tissue culture was optimized and selected. When 6-BA and NAA were in low concentration, the plantlets grew slowly and the differentiation multiple of the cluster buds were in low level. When 6-BA and NAA were in high concentration, the plantlets grew quickly and the differentiation multiple of the cluster buds were in low level. The cluster buds were proliferated preferably and subcultured on the proliferation medium containing 0.5 mg/L BA and 0.1 mg/L NAA.3. The medium properly added NAA could induce the plantlets to grow more lateral root and root hair. Additionally, the buds were rooted normally on medium containing 0.5 mg/L IBA and 0.1 mg/L NAA, and the plantlets could normally root and survive after transplantation.4.Shoot tips excised from healthy in vitro plants of M.sieversii were successfully cryopreserved by the vitrification technique. A suitable procedure was established as follows: four weeks after subculture, shoot-tips about 2– 3 cm in length were precultured for 3 days on MS medium supplemented with 0.4 mol/L sucrose and 5% DMSO, and pretreated in 60% plant vitrification solution (PVS2) for 30 minutes at room temperature, then followed by dehydration with PVS2 for 40 minutes at 0℃and put into liquid nitrogen for 24 hours. The survival and regeneration rate of shoot tips treated in this way was 93.3% and 86.7% respectively. Almost all the shoot tips formed roots and were successfully transferred to soil in pots. The plantlets could normally root and survive after transplantation.5.In vitro cultured M.sieversii was used to study on genetic stability after cryopreservation from the prespective of morphology and molecular biology. Results showed that there were no significant difference on leaf area, leaf colour, leaf figure, plant height and stem diamerer between the treated plantlet and its control. And DNA polymorphism was not different by SSR. Therefore, we could conclude that genetic stability of M.sieversii was not altered after cryopreservation.
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