| Larix Chinensis Beissn, the perennial and ligneous plant species, belongs to genus Larix mill and distributes only on the peak of Mt. Qinling with the limited altitude 2800-3500m, and it had been listed as second grade plant species of state in need of conservation. L. Chinensis, as the only deciduous and coniferous forest and important water-nurturing forest located on the top of other forest in Mt. Qinling, has important conservative and research value on the respect of species conservation, scientific research, ecology and economy. In the past, because the studies were limited in the area of surveying and morphological describing, and few researches were carried on conservative genetics, scientists knew very little about genetic structure and genetic diversity in natural populations of L. chinesis. This paper, using allozyme as the molecular mark, mainly deals with genetic structure and genetic diversity in natural populations of L. chinesis, foresee its genetic destiny and research its probably endemic reason, with the aim at providing beneficial reference for the protect of L. chinesis.Using 8 enzymes (Peroxidase, Superoxide dismutase, Malate dehydrogenase, Shikimate dehydrogenase, Glutamate dehydrogenase, Catalas, Malic enzyme, Amy) which result in 15 gene loci, 120 individuals from 6 populations were analyzed with allozyme, and the results indicate that percentage of polymorphic loci(P) is 66.7%; mean number of alleles per locus(A) is 1.71 ( vary from 1.67 to 1.73 with population ) ; effective number of allele per locus, (Ae) is 1.63(range 1.47～1.68 )；Shaanon index is 0.46(range 0.39 ～ 0.48); mean expected heterozygosity per locus (He) is 0.32(0.28 ～ 0.34); mean observed heterozygosity per locus (Ho) is 0.3322( 0.32～0.34). According to mean expected heterozygosity per locus, the sequence of genetic variation of six population is Taibaishan population > Guangtoushan population > Yuhuanshan population > Niubeiliang population > Zhuque population > Foping population. FIT= -0.03 (total population), FIS= -0.07 (in population), ratios of gene diversities of heterozygosities FST=3.32%(among population),it is, approximately 96.8％genetic variability exists within populations and only about 3.32％ genetic variability lies among populations. They show that only a little genetic differentiation was found among population which correspond to wind-pollinate, outcrossing species of L. Chinesis. Based on FST , mean gene flow Nm is about 7. 3. Nm>1, it is enough to resist the effect of genetic drift and prevent population from subdivision. Analysis of Nei(1978)genetic identity and genetic distance show that genetic identity(I)among population of L. Chinesis is very high with a mean of 0.99(0.95～1.00), and mean genetic distance (D) is 0.01(0.00～0.05). Again, they show that high genetic similarity was found among population of L. ChinesisDendrogram resulting from UPGMA method clustering based on Nei (1978)genetic distance shows that the six population are divided into two branch: Foping and Zhuque population cluster into one branch showing the two population has high similarity. Other populations cluster into the other branch, of which, Taibaishan and Yuhuangshan population cluster on the first grade, Taibaishan, Yuhuangshan and Guangtoushan populations cluster on the second grade showing high similarity among them; Niubeiliang population is somewhat independent. Fixation indices (F value) change widely from -0.20to -0.01 with a mean of --0.07. For most of F values are negative, it means population was heterozygote excess compared to expected random mating, and this may be in relation with main reproductive mode of outcrossing in L. Chinesis. Outcrossing rate (t) is 1.1, more than 1, indicating that individual receiving different genotype pollen is randomly and imply that L. Chinesis may be self-incompatible. Based on the results of allozyme above and compared with other Larix species, L. chinesis is on the middle genetic diversity level. However, L. Chinesis belong... |
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