| Daba mountains located in the midwest of China is at the border of north and south climate and the border of Sichuan, Shanxi, Hubei, Chongqing Provinces(municipalities),which in the east of river valley that Han-river flows through. It is at the interchange of transition zone between eastern level plain and the secondary plateau mountain.So there are diversity of terrain, rich climate changes and various species of plants. Walnut genus(Juglans)here are characteristic non-wood foresty species, which have more than 2000 years cultivation history according to the record. Long-term natural reproduction of them breeds abundant genetic resources.On the basis of literature review, this study tried to interpret cultivated walnut species diversity and genetic structure more comprehensively in Daba mountains, using natural seeding trees as the research object especially cultivated species with identifying method by nut phenotypic traits and SSR molecular markers, compared with the existing domestic walnut of cultivated varieties. The main results were as follows:1. The types, distribution and management characteristics of seeding walnut species were ascertained. And the distributing center and concentrationof seeding walnut types were demonstrated. We investigated related information of walnut resources in 50 counties(city,area) which are administrative division units, covering 100% distribution area of walnut. The results showed that: There are 6types of Juglans genus in Daba mountains including J. regia,J.cathayesis, J. sigillata, J. mandshurica, J. hopeiensis,which are native to China, and "middle type" of J. regia. andJ. sigillata. which is not reported. Among them, J.regia.,J. sigillata and "middle type" are the main cultivated types in this area. The tree body, leaf characteristics,phenological period, properties of fruits and nuts of the seeding types have abundant variations.And the quantitative traits of nuts basically cover the known walnut resources in our country.Distribution of seedingtypes here are consistent with terrain generally, which present continuous in the horizontal direction and at an altitude of 250 m ~ 1 800 m range in vertical direction. The main distributing center and sub distributing center of seedingtypes respectivelyare in the western section called Micang mountains and southeastern section called Wushan-Shennongjia-Wudang-Jingshan mountains. J regiais widely distributed in Daba mountains. J. sigillata.distribution is at an altitude of 250 m ~ 500 m in the southeast of Daba mountains. The concentration distribution of middle type is in the middle part of Daba mountains(Daba moutains with narrow definition).Due to disturbance for a long time by human, seeding types are mainly scattered existence, and the normal fertile of which mainly at the " four sides" and in the terraces.2. Specific germplasm screening methods based on nuts phenotype diversity were established, which is useful for scientific utilization of the germplasm resources in this region.The coefficient of nuts morphological differentiation between seeding population of seeding walnut types in this region is 8.89%. And the coefficient of variation between them are68.29% ~ 104.05%.Although the clustering results of Manhattan distance of nuts phenotypic traits with geographic distance was not completely consistent, there was positive correlation between them. The nuts average variation abundance in eastern is higher than that in western with the border of Chengkou county, which is the distribution center of nuts resources. For the size of nuts, nuts weight of cultivated types is between 4.11 g and 22.87 g, with an average of11.67 g, accompanied by core-shell thickness from 0.55 mm to 2.38 mm. So nuts size of cultivated types in Daba mountains has basically covered the known walnut germplasm resources,including relatively abundant nut-small and thick core-shell resources. We observed80 features of 17 nuts quality traits, variation coefficient of which is between 33.48% and262.59%. Eight nut common factors of cultivated types including size factor, kernel-taken difficulty factor, shape-regular factor, kernel-output factor, even and plump factor, handsome factor, cross-section and base-perpendicular-to-suture factor, apex-perpendicular-to-suture and kernel-color factor were determined by comprehensive factor analysis of phenotypic characters.Seven big and easy to kernel-taken samples, eight small and easy to kernel-taken samples, four big and shape-regular samples were selected by using common factor 1, common factor 2 and common factor 3.And ten excellent samples were selected by using comprehensive score of common factors.3.Identifying methods of seeding walnut types were established using phenotypic and molecular markers. Five phenotypic markers of nut standard quality traits including shape in longitudinal section perpendicular to suture and 16 SSR molecular markers including WJR069 were selected using in the methods. And 2 phenotypic markers and 2 SSR markers of which were used to establish fingerprint for selected 50 germplasm.4. High genetic abundance of seeding walnut types in Daba mountains was confirmed.And on this basis, the core collection building methods was discussesed. The observed allele number(Na) of Seeding populations of walnut in Daba mountains is between 4.94 and 4.94,with an average of 6.27. The effective alleles number(Ne) is between 2.93 and 2.93, with an average of 3.28. Shannon index is between 1.112 and 1.112, with an average of 1.324. The observed heterozygosity ranged from 0.391 to 0.453, with an average of 0.437; And the expected heterozygosity ranged from 0.612 to 0.612, with an average of 0.688, which is higher than that of nine population from Shanxi, Sichuan, Chongqing and Yunnan et al.(He=0.525)and that of J. regiapopulation in Tibet(He = 0.5864). In addition, the genetic abundance of walnut population in southeast section of Daba mountains is higher than other sections. So southeast section of Daba mountain is concentrated distribution area of walnut genetic resources. The genetic differentiation among populations is small with the differentiation coefficient(FST) range from 0.0334 to 0.1491,with an average of 0.0632. Core collection built based on genetic diversity analysis by using the sampling strategy of preliminary site and Nei’s standard genetic distances is superior to other sampling strategy and genetic distance. Core collection built in this study contains 35 samples which retains 9.07% of the original samples.The retentionrate of polymorphism loci percentage, observed allele number, effective alleles number, Nei’s genetic diversity index and Shannon information index achieve or exceed 100%.5. A batch of excellent germplasm including 70 clones and 35 seeding family offspring were selected and ex-situ conserved, which can offer the basic materials for the walnutgermplasm selection in this region. |
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