| The industry of silkworm and mulberry is of great importance for formers to get rid of poverty and become rich in some areas of China.The quality of silk is the main basis of competence international wide .Nevertheless, the output and quality of silk are affected directly by the yield and quality of mulberry leaves.The breeding of artificial triploid mulberry (2n=3x=42) has become the highlight in the breeding of mulberry because of its excellent economic charaters and agronomic charaters which are prior to that of diploid mulberry (2n=2x=28) and natural triploid mulberry (2n=3x=42).In order to obtain new breeding which high production and good quality of leaves, it is necessary to study the breeding parents and its genetic backgroun.But mulberry is a kind of ligneous plant which is parennial, extendotropic and having high heterozygosis in genotype. So, it is difficult to study its genetic laws and genetic background with common methods. In this study , genetic background of Jialing16, Jialing20, their parents and Jialing20 brothers are analyzed by the AFLP(Amplified Fragment Length Polymorphism),from which the genetic distance , similarity coefficient and UPGMA dendrogram of the materials are obtained.These will provide reliable evidence for the selection and tissue mating of parents. These will be helpful in the breeding of new artificial triploid mulberry with strong heterosis and miltiploid superiority. Results and conclutions of study are as follows:1. By AFLP analysis of Jialing16, Jialing20 and their parents , it is found the similarity coefficient between 7920 (2X: o)and Tongxiangqing(4x: o ), which are parents of Jialing20, is 0.6612 and the similarity coefficient betweenXiqingl (4x: o ) and Yu2 (2X: o ), which are parents of Jialing16, is 0.6607.By studying AFLP analysis of Jialing16 , Jialing20 and their parents.We come to the conclusion that the ideal genetic similarity coefficient between the mother and the father of F1 is about 0.6600, which can be seen as an evidence reference for the selection of hybrid parents in theprocess of multiploid and hybrid breeding .2. By AFLP analysis of Jialingl6 and their parents , Jialing20 A (3x;F1), B(3x;F1), C(3x;F1), 10 diploids(2x;F1) and their parents (P) .It can also be found that the FI generation has nearer genetic relationship with diploid parents.It is probably because that generation gets more genetic substance from diploid parents than that from teroploid parents.As a result , it should be put more importance on the selection of diploid parents, which should has high quality in economic character , argronomic character and with strong vital capcity.3. By analysis, it has been noted that the filial generation are better in fertility seeds germination capacity and genetic transmission capacity when taking diploid as female parents better than taking diploid as male parents.So, it is better to choose diploid as female parents when pairing the hybrid parents.4. By AFLP analysis of this study , according to former study on its chromosome at the cellular level as well, it is considered that the reason for diversity of diploid (3x)and triploid(2x)in F1 generation of 2xX4x or 4xX2x and the reason for high polymorphism and complex dendrogram between dilploidsand triploids are that unbalanced separation has taken place in the number and the content of chromosomes of autotetraploid, which cause partial sterility and diversity in genetic substance and the number of its progeny's chromosome.By the analysis of genetic distance. Genetic similarity coefficent and their UPGMA dendrogram of the 3 triploids, 10 diploid and their parents. We suggest , in order to obtain early indentification AFLPanalysis may be used to analyse genetic banckground of F1 generation and identify Fl whether is the proper one that we needed.5. According to the results of this study and former studies , we propose a hypothesis about the diplosis evolution of mullberry derived from diploid at first, then derivated other kinds of indi...
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