| Betula albosinensis is one of the main group establishing tree species and silvicultural pioneer tree species in the high altitude forest areas of northwest China.In recent years,the demand of Betula albosinensisis seedlings has been increasing due to the vegetation restoration of alpine forest in northwest areas of China.Therefore,it is of great significance to carry out cross breeding of Betula albosinensisis new varieties for ecological construction.In this paper,the Betula albosinensis secondary forest in Jialing River Source Scenic Spot,Baoji City,Shaanxi Province was selected as the research object.Three sample plots with gradients of elevation（2400m,2100m,1800m）were set up.The method of observation of sample plots and individual plants was adopted to conduct comparative observation of flowering phenology for one and a half years starting from July 2021.The sucrose concentration,boric acid concentration and culture temperature suitable for germination of Betula albosinensis pollen were obtained,and the method for rapid detection of its vitality under field conditions was also explored.At the same time,the storage effect of pollen was discussed from the aspects of water content,whether the container was vacuumed or not,and storage temperature.In addition,research was conducted on artificially controlled pollination and the growth of its offspring during the seedling stage.In order to lay a foundation for cross breeding and germplasm innovation of Betula albosinensis.The main results are as follows:（1）Flowering phenology of Betula albosinensis in this region:The male flower bud extends in mid-July and entered dormancy state in late September.It continued to grow after breaking dormancy in early April of the next year,and entered the initial flowering stage in early May.The entire initial flowering stage lasted for 5 days and then entered full flowering stage,Loose powder ends on May 18.The female inflorescence extended at the same time with the new leaves in early May,the growth was slow at the beginning.From May 11 to May 20,the growth of the female inflorescence accelerated,and from May 20 to June 16,the growth of the female inflorescence slowed.The stigma bracts began to open on 18 May,fully opened on May 22,slightly rolled red on May 23,fully rolled on May 28,and pollination ended.At the individual plant level,the average flowering period of Betula albosinensis was about 13 days.The flowering period of 2400m altitude and 2100m altitude was same,but about 10 days shorter than that of 1800m altitude.At the stand level,Betula albosinensis in and around the forest margins at 2400m and 2100m altitude entered full bloom in early mid-May,while at 1800m elevations,Betula albosinensis entered full bloom from late May to early June.（2）Germination conditions and germination characteristics of Betula albosinensis pollen:the optimum medium and culture temperature for in vitro germination of Betula albosinensis pollen are 10 g·L-1agar+15%sucrose+250 mg·L-1boric acid and 30℃;After culturing for 12 h under this condition,the pollen germination rate and pollen tube length tended to be stable,and the pollen tube length reached 98-102μm.（3）When TTC method,I-KI method and acetic magenta method were used to rapidly detect the pollen vitality of Betula albosinensis,when the p H value of TTC staining solution was 7.0,there was no significant difference between the detection results and in vitro germination method,which was suitable for rapid detection of pollen vitality in the field.（4）The viability of Betula albosinensis pollen was significantly different under different storage temperatures,and it could only survive for 7 days at room temperature（18-30℃）.After storage at 4℃for 1 month,it was basically inactivated.When stored at-20℃for 180 days,the germination rate of pollen was only 20.6%.When stored at-40℃and-80℃for 180 days,pollen germination rate remained above 40%.After drying and vacuuming,the activity of Betula albosinensis pollens was higher than that of untreated pollens,but the difference was not significant.（5）The best time for pollination is when the stigma of the female inflorescence of the Betula albosinensis begins to secrete mucus or the bracts begin to open and slightly curl red;The seeds can be harvested when the fruit sequence changes from green to golden or yellowish brown and seeds are scattered when shaken lightly.The 1000-seed weight of pollinated seeds was significantly different within the parent and between the parent and the parent（P<0.01）.There were significant differences in seed 1000-grain weight,germination rate,germination potential,seedling height and ground diameter between most hybrid combinations and control group,showing certain heterosis. |
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