| The ancient tea plantations in Baiying Mountain,Yunnan province,is an important concentrated distribution area of ancient tea plants in the Lancang River Basin in which to preserve a large number of ancient tea germplasm resources with various species and variations.Baiying Mountain is a tea treasury where witnessed the historical origin of tea cultivation.The tea plants resources in the concentrated distribution area of ancient tea plants play a crucial role in germplasm innovation and variety protection.In order to study the genetic diversity of tea germplasm resources in Baiying Mountain,this study took six representative groups of tea plants of Baiying Mountain,Benshan tea(BS),Ergazi tea(EGZ),Heitiaozi tea(HTZ),Baiyazi tea(BYZ),Mengku tea(MKC)and Liuye tea(LYC)from Baiying Mountain as materials.The phenotypic traits and biochemical components of all groups of tea plants were observed measured and determined.In addition these,genetic diversity analysis also was performed using SNP markers.The main results were as follows:(1)Phenotypic trait determination analysis.The tree types of 60 tea plants of six groups in Baiying Mountain are dungarunga,arbor and shrub.the tree types of BS,EGZ,HTZ and MKC are mainly arbor and dungarunga,while BYZ and LYC are shrubs.The average leaf length,leaf width and leaf area respectively are 8.32～13.69 cm,4.09～5.56 cm and 23.60～55.50 cm2.The average corolla diameter is 3.07～5.81 cm,the average petal number is 5.92～9.62,the petal color is mainly white with a little light green.The average ovaries number is3.00～4.77 and the average style length is 0.99～1.91 cm.Phenotypic traits vary greatly that MKC tea is distinguished by large leaves and small flowers,LYC is characterized by lance-shaped leaves,small flowers,low stylopodia and lower pistils than stamens,BS,EGZ and HTZ are distinguished by their large flowers,large number of ovary cells and higher pistils than stamens;BYZ is all shrubs,with flat leaf margins and light green flowers.The genetic diversity index of descriptive phenotypic traits ranges is 0.00～1.09,with rich variations in traits such as relative height of pistils and stamens,petal texture,leaf surface,and leaf growth status.The variation amplitude of numerical traits ranges is 0.46～55.63 and the coefficient of variation ranges is 3.58%～32.56%.There are significant genetic differences in leaf area,style length,and corolla diameter.(2)Biochemical component content determination analysisBased on the results of the biochemical components of the new buds in spring and summer were integrated,and the new buds of various groups were abundant in biochemical components.The water extract content is 38.54%～47.44%,the tea polyphenol content is 25.07%～39.60%,the amino acids content is 3.04%～6.07%,the caffeine content is 9.33～19.07 mg/g,the ellagic acid content is 0.25～1.39 mg/g,the gallic acid content is 1.19～9.21 mg/g,the theophylline content is 0.07～0.27 mg/g,total flavonoids content was 1.24～3.61 mg/g and the total catechin component content was 54.81～177.64 mg/g.According to the evaluation index of specific germplasm resources,there are high tea polyphenol,low caffeine and high amino acid specific resources in Baiying Mountain tea plants taxa,which can be used as breeding materials.The magnitude of variation in the content of 19 biochemical components ranged from 1.08 to 128.54,and the coefficient of variation ranged from 5.61% to42.59%.The highest mean coefficients of variation respectively were 42.59%,25.46% and 25.46% for total catechins.The biochemical composition content of tea germplasm resources exhibited abundant genetic diversity.(3)Genetic diversity analysis.A total of 1706252 SLAF tags was developed by SLAF-seq technology for simplified genome sequencing,with an average sequencing depth of 18.55×,of which there were 175804 polymorphic SLAF tags,yielding a total of 3064470 population SNPs.The phylogenetic tree based on population SNP divided 48 tea plants into 3major clades.The lowest cross-validation error rate was observed for the number of population structure subgroups K=3.Principal component analysis divided the sample individuals into 3 population subjects.G-matrix analysis visualizes the kinship of various groups.BS is more distantly related to other groups of tea resources,BYZ,LYC and MKC are more closely related,and HTZ and EGZ are moderately related to BS and BYZ tea.In addition,EGZ and HTZ are the two major taxa with more confusing kinship and more complex genetic composition.The minor allele frequency(MAF)was 0.28 to 0.29,the expected number of alleles(Ne)was 1.21 to 1.43,the expected heterozygosity was(He)0.12 to 0.25,the number of polymorphic markers was 117283 to 278821,the nei diversity index was(Nei)0.14 to 0.28,the observed number of alleles was(Na)1.32 to 1.66,the observed heterozygosity was(Ho)0.06-0.11,the polymorphic information content was 0.09 to 0.20,the Shannon Weiner diversity index(I)was 0.18 to 0.37,and the level of genetic diversity based on SNP markers was low.To sum up,the tea germplasm resources of Baiying Mountain showed obvious genetic differences in phenotypic traits.The traits such as tree shape,relative height of stamens,petal texture,leaf surface,leaf attachment status,leaf area,style length and corolla diameter have great potential for screening tea germplasm resources.The content of biochemical components showed abundant diversity with a large magnitude of of variation and coefficient of variation.The components leading to the differences mainly include total catechin,TP,EW and GA,which can be used as an important basis for the screening of tea germplasm resources.Low level of genetic diversity of SNP markers.The genetic diversity level of SNP markers is relatively low,the resource variation is small,and there is a certain inbreeding rate within taxa.BS is distantly related to LYC,MKC,BYZ,while LYC and MKC have a medium to high level of consanguinity. |
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