| Betula platyphylla is very cold-resistant, fast-growing and has a good adaptation to different kinds of environments. It is an extremely important tree species in China. To protect the fine germplasm resources of Betula platyphylla and keep its sustainable genetic improvement, the genetic diversity of populations in were studied by there molecular markers in this paper. The main results show that:1.Genetic diversity analysis by different primer number15 Betula platyphylla populations, each of which has 20 individuals, were amplified with 5,7,9,13,15,17 SRAP primers. The results show that:different primer numbers brought very significant and significant impact for all locis, the number of polymorphic locis, genetic variation within populations, genetic variation among populations and gene flow and brought few impact for percentage of polymorphic loci.Different primer numbers brought some impact for genetic distance and cluster. When the number of primer is 4, the distance between Qingyuan ang Ningxia is the smallest and the distance between Liangshui and Wuyiling is the biggest. When the number of primer is 7, the distance between Moerdaoga and Huanren is the smallest and the distance between Liangshui and Dongfanghong is the biggest.15 populations were clustered into 4 groups and genetic relationship is different. When the number of primer more than 11, the distance between Moerdaoga and Huanren is the smallest and the distance between Liangshui and Caohekou is the biggest.15 poputions were clustered into 5 groups and each branch contains the same members.2. Genetic diversity analysis by different sample sizeEach population contains 4,8,12,16,20 samples respectively, were amplificated by 17 SRAP primers, the results show that:the different impact were brought by different sample size, different sample size brought significant impact for percentage of polymorphic loci, genetic variation within populations and genetic variation among populations and brought few impact for all locis, polymorphic locis and gene flow.Sample size brought some impact for genetic distance and cluster. When the sample size more than 8, the two poputions that the smallest and the biggest genetic distance between are the same. When the sample size is 4, the distance between Qingyuan and Ningxia is the smallest and the distance between Huanren and Wuyiling is the biggest. And 15 populations were clustered into 6 groups.3. Genetic diversity analysis of Betula platyphylla by different molecular markers(1) the result is different by different mocular marker 15 Betula platyphylla populations, each of which has 20 individuals, were amplified by 15 RAPD primers,15 ISSRprimers and 15 SRAP primers, the results show that:when the primer number and sample size are the same, different molecular markers brought different genetic parameters. RAPD marker were amplified 186 locus, an average of 12.3 bandings are amplified with one primer, There are 185 polymorphic loci and the percentage of polymorphic loci is 99.46%. The total gene diversity (Ht) of all populations is 0.2394,the gene diversity within populations (Hs) is 0.1948 and coefficient of gene differentiation(Gst) is 0.1862, 81.37% of the genetic variation of Betula platyphylla is within populations and 18.63% is among populations.ISSR marker were amplified 127 locus, There are 124 polymorphic loci and the percentage of polymorphic loci is 97.64%. The total gene diversity (Ht) of all populations is 0.3438,the gene diversity within populations (Hs) is 0.1892,55.03% of the genetic variation of Betula platyphylla is within populations and 44.97% is among populations. SRAP marker were amplified 120 locus, There are 118 polymorphic loci and the percentage of polymorphic loci is 98.33%. The total gene diversity (Ht) of all populations is 0.2623,the gene diversity within populations (Hs) is 0.1730,65.96% of the genetic variation of Betula platyphylla is within populations and 34.05% is among populations.(2) the different correlation of genetic parameters by different molecular markersBesides effective number of alleles(Ne), the correlation of all parameters between ISSR and RAPD and the correlation of all parameters between ISSR and SRAP were significant or very significat. The correlation of all parameters between SRAP and RAPD are not significant.(3) the genetic distance and cluster among populations by different molecular markersDifferent markers brought different genetic relationship and cluster results. RAPD show that:the genetic relationship between Huishan and Caohekou is the closest, the genetic relationship between Moerdaoga and Xinjiang is the farthest. ISSR show that:the genetic relationship between Qingyuan and Ningxia is the closest, the genetic relationship between zhuoer and Xinjiang is the farthest. SRAP show that:the genetic relationship between Moerdaoga and Huanren is the closest, the genetic relationship Caohekou and Liangshui is the farthest.15 populations were clustered into 6 groups by RAPD marker, but 15 populations were clustered into 5 groups by ISSR and SRAP markers and the populations of each group are not the same.
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