Genetic Diversity Of Germplasm Resources On Walnut In Tibet Region

Germplasm resources are the basis of plant breeding for new variety. There are plenty of Juglans regia landrace and Juglans sigillata natural forests distributing in Tibet area. It is the natural genetic resources of walnut, and valuable for Germplasm resources exploration. The distribution pattern, resources character, genetic diversity, genetic structure were studied based on the aspect of community composition, Phenotype, nutritional components, Phenophase, molecular markers. To apply the scientic basis for resources utilization and protection. Major results are described as follow:1. Through the field survey, we found that there are 3 different kinds of species of Juglans in Tibet.(Juglans regia, Juglans sigillata, Juglans cathayensis). Juglans cathayensis have distributed in fragmentary place with minute quantity, in Jilong country of Rikaze area and Dongjiu country of Linzhi area. Juglans regia landraces have distributed in two sub-areas, the southern and southeastern parts of Tibet. it mainly distribute along the up and middle reaches of Yaluzangbu river(in the southern part) and up reaches of Nujiang and Lancangjiang river(in the southeastern part). The vertical scope of Juglans regia is between 1500-4100m in altitude, concentrated distribution is between 2200-3500m. Juglans sigillata mainly distributed in the area of northern slope of Himalayas, southeastern part of Nyainqentanglha Range and downstream of Yaluzangbu river. The vertical scope is between 1800-3400m. Juglans sigillata landraces have mixed with Juglans regia landraces along the middle reaches of Yaluzangbu river, which from Milin to Bomi. Juglans sigillata natural forests mainly distributed in the forest region from Dongjiu to Suotong village in Linzhi area, which altitude range is between 2200-3200m. In addition, there are still a few natural forests distributing in Jilong,Yadong,Cuona,which are all in the subtropical area of southern slope of the Himalayas2. The results of walnut community component indicated that there were 33 families of seed plants, including 47 genera and 55 species in walnut community. The dominent families were Rosaceae and Compositae. There were three plant layers of walnut forest community, the tree, shrub and grass. the number of individuals in shrub layer and middle–under layer of tree layer were dominant. Interlayer plants was sparse. The associated deciduous trees are main Compositae and Rosaceae and associated Evergreen trees are main Araliaceae and Fagaceae. In tree layer, the important value of walnut is 161.63, which is the highest of all the species, the second is Quercus tungmaiensis,52.54; the third is Myrsine semiserrata, 26.08. It suggested that the walnut possessed the absolute advantage status in the community, then restrained the growth of other species, and made the community component more simple. ).Based on the DBH class frequency distribution patterns,the population age structure of the different tree species were categorized into different regeneration types.According to the biological and ecological characteristics,the population regeneration types of walnut were Bimodal, which predict the population will develop toward the community climax as the dominant species. At the same time.The population regeneration types of Quercus tungmaiensis were Pyramid, means that its population got the increasing trend.4. The diversity analysis of nut phenotype of J. regia landrace in Tibet showed that the nut weight got the highest value of variation in the 9 quantitative traits, the variation coefficient was 27.32%. the second was 22.0% of the hust thickness, and the lowest is 10.8% of nut width. three qualitative traits didn't have too many types. Most traits showed strong relationship between each other. According to principle component analysis,the first three main component made the contribution of 82.8% to variation. High level of diversity was detected from 12 nut traits, with an average variation of 8.17 and an average Shannon2weaver index (I) of 1.834 based on morphological traits. Population structure within the subcollection of 86 individuals has been defined, and 5 clusters were identified based on various phenotypic variations by using Structure 2. 2 software.5. The fat analysis of J. regia landrace in Tibet showed that the range of total fat was 64.61-74.36g/100g, with average 70.28g/100g. and the the range of Saturated fatty acid was 3.92-9.56g/100g, Monounsaturated fatty acid was 12.15-29.23 g/100g, Polyunsaturated fatty acid was 24.27-50.4 g/100g, Unsaturated fatty acid was 51.45-67.79 g/100g. the composition of fat showed a high extent of variation, and the difference of Monounsaturated fatty acid accounted for most of it. the content of Monounsaturated fatty acid in Tibet was high with average19.86 g/100g,and Polyunsaturated fatty acid was in middle level with average41.6 g/100g. the ratio ofω-6/ω-3 3.83-7.33,concentrated on 4.0-6.0,which were suitable for human being absorption. All the variation among populations didn't attain the significant level except the saturated fatty acid.6. The flowering phenological period investigation suggested that the earliest flowering area is Langxian, which the Staminateflower blossomed on 10th April, Pistillate flower blossomed on 8th April. The latest flowering area is Milin, which the Staminateflower blossomed on 26th April, Pistillate flower blossomed on 28th April. In total 256 trees, the ratio of protandrous was 54.3%, protandrous was 54.3%, protogynous was 45.7%. there were 10.55% plants possessed the traits of lateral branch fruiting. The ratio of 2–3fruits per branch was 91.27% , 5 fruits was 7.55%, 10 fruits was 1.18%. the range of male inflorescence lenth was 5.8-24.2cm, with average 12.9cm. The number of flowers per male inflorescence WAS 72-156, with average 112.4.7. A moderate to high level of genetic diversity was observed at J.sigillata population levels in Tibet with the total number of alleles 107, which possessed 90.68% of total alleles in the J.sigillata population, and average 8.92 for per locus. Effect number of alleles per locus was 3.92. The total value of expected heterozygosity (He) within population in Tibet was 0.678. The percentage of polymorphic loci(P) was 100%. The sequence of genetic diversity of the 5 populations was LY>LJ>PL>JL>MN. The population distributed in the Tibet of China had a higher genetic diversity than the populations in other places. The proportion of genetic differentiation presented among Tibet populations accounted for 5.9% of the whole diversity, and average gene flow (Nm) was 4.021. The index of Fit and Fis of J.sigillata population in Tibet was 0.068 and 0.01, which indicated that their heterozygote was slight deficiencyA moderate level of genetic diversity was observed at J.regia population levels in Tibet with the total number of alleles 131, which possessed 91.61% of total alleles in the J.regia population, and 25 of them were private. Average number of alleles per locus was 10.92 and effect number of alleles per locus was 3.53. The total value of observed heterozygosity(Ho) and expected heterozygosity (He) within population in Tibet were o.479 and 0.605. The percentage of polymorphic loci(P) was 100%. The sequence of genetic diversity of the 9 populations was ZD>MK>BM>BY>LX>JC>FY>ML>GL. Most population distributed in the Tibet of China had a higher genetic diversity than the populations in other places. The proportion of genetic differentiation presented among Tibet populations accounted for 11.4% of the whole diversity, and average gene flow (Nm) was 1.946. The index of FIT and FIS of J.regia population in Tibet was 0.163 and 0.055, which indicated that their heterozygote was deficiency.In 86 J.regia landraces of Tibet, 119 alleles were detected based on 12 SSR primers and the average number of alleles per locus Na=9.92, the effective number of alleles Ne=3.34. The number of alleles in J.regia landraces account for 90.84% of total alleles number in Tibet. The expected heterozygosity (He) was 0.588, which was little lower than that of total J.regia population in Tibet(He=0.605). The cluster results based on SSR marker was not in accordant with the their geographic distribution, nor was the cluster results based on phenotypic data.8. The results of SSR marker and ITS sequencing suggested that ITS sequencing presented only 7 variable loci which only one polymorphic loci between the two species in 645bp length. Based on 65 alleles generated with SSR, genetic distance between populations was calculated. The closest genetic distance was 0.119 found between SJC and QZ population, and the furthest distance was 0.552 found between MN and HS population. The genetic distance of intro-species was similar to that of inter-species, and the difference between two species was quite small and showed no significant. Those results suggested that the two species might be different eco-types.