Study On Genetic Diversity In Populus Yunnanensis And Differentiation Among Sections In Populus

Poplar is a general name of all tree species in genus Populus L. of family Salicaceae and is characterized by rapid growth, high adaptability and wide employment. It has been cultivated in many countries and become one of the tree species with the broadest distribution and the highest timber production in the mid-latitude areas. Poplars are abundant in China, accounting for over 50% of the total resources. Many species in section Leuce and Tacamahaca are indigenous and widely distributed in China. Full employment of these genetic resources is of significance for the improvement and the breeding of new varieties or cultivars. In this study, 120 clones of P. yunnanensis from four provenances were used for the analyses of genetic diversity and genetic structure and for the comparison of diversity level on both allozyme and DNA levels.Meanwhile, 54 poplar clones from section Leuce, Tacamahaca, Aigeiros and Turanga were studied using AFLP analysis for identification of inter-section differentiation. This study laid a scientific foundation for both the inter- and intra-section cross breeding. The main results are described as follows:1. A total of 120 clones of P. yunnanensis from four natural populations were used for the horizontal starch-gel electrophoresis with eight enzyme systems. 13 clear bands were observed in the gel, of which 12 bands demonstrated polymorphism, thus the polymorphic index (P) is up to 92.31%. 29 alleles were detected, average effective alleles (Ae) was 1.8858. The expected heterozygosity (He) was 0.4461, and Shannon's information index (I) was 0.6416. At inter-population level, the estimates were P=92.31%,A=2.231,Ae=1.934,He=0.4518,I=0.6619. The genetic similarity among populations ranged from 0.9566 to 0.9964, and genetic distance from 0.0036 to 0.0443. The genetic differentiation coefficient (Fst) was only 0.0254, indicating the high similarity among different populations of P. yunnanensis. 97.45% of genetic diversity originates from the differences of individuals within population. A UPGMA dendrogram, based on the genetic distances, were constructed in four populations of P. yunnanensis. Four populations were separated into two groups according to their geographic distances, the population LIJIANG and population DALI in the first group, and population KUNMING and population XUANWEI in the second group. The allozyme analyses showed that there were rich genetic variations among individuals within populations of P. yunnanensis.2. AFLP analysis was carried out in a total of 120 individuals from four populations of P. yunnanensis with 11 primer combinations. 1,006 AFLP bands were observed, of which 692 makers showed polymorphism. The percentage of polymorphism (P) is 68.79%. 1.418 alleles and 1.174 effective alleles were detected in each locus. The Nei's index (H) and Shannon informative index are 0.105 and 0.162, respectively. According to genetic divergence of populations, GST=0.2591, the variation among population contributes 25.91% of the total variation and the other 74.09% exists among...