Genetic Variation Of Taxus Wallichiana Var.mairei Natural Populations And Families

Taxus wallichiana var.mairei(Lemee H.Leveille.)L K Fu et Nan Li is a rare and endangered tree species that integrates timber,medicinal and ornamental,and is also a valuable timber plantation tree that has been promoted in southern China.Understanding the phenotypic variation,genetic diversity and genetic structure of natural populations in the main distribution areas of T.wallichiana var.mairei will help to formulate strategies for the evaluation and protection of the core genetic resources of T.wallichiana var.mairei.The selection and breeding of fast-growing high-quality varieties provides the basis for preliminary research.The main findings are as follows:(1)Phenotypic variation of needle phenotype traits in natural populations of T.wallichiana var.maireiThe study of 5 needle phenotype traits,needle nitrogen and phosphorus content(LNC、LPC),and nitrogen to phosphorus ratio of needle(N/P)of 670 samples from 18 natural populations of T.wallichiana var.mairei showed that the variation of 5 needle phenotype traits was extremely significant between and within populations,among which the maximum and minimum variation coefficient was needle width to length ratio(29.56%)and needle width(12.79%),respectively.The variation among populations(24.94%)of needle phenotype traits was less than the variation within populations(75.06%),the phenotypic differentiation coefficient for needle phenotype traits was varied from 15.25%to 43.48%.The average values of LNC,LPC,and N/P in each population were 17.82 g/kg,1.21 g/kg,and 15.03.The N/P values in some populations were less than 14,indicating that its growth is mainly limited by the nitrogen,and the N/P values in some populations were more than 16,implying that phosphorus also affects needle growth.The leaves of T.wallichiana var.Mairei populations in the eastern part are shorter than those in the populations of the middle and west,and the N/P is also smaller,while the population of higher altitudes has a smaller LNC,and the population with a large range of monthly average temperature and a large range of annual temperature changes has thinner leaves.The results of Ward clustering based on needle phenotype traits showed that the 18 populations were clustered into 2 major groups,4 subgroups.The populations of the first major group are mostly in the east,and the populations of the second major group are in the middle or Midwest.(2)Genetic diversity of natural populations of T.wallichiana var.maireiUsing 13 SSR primers to study the genetic diversity of 665 samples of 18 natural populations,the results showed that a total of 291 alleles was detected.At each point,the averaged number of alleles(Na),expected heterozygosity(He),polymorphic information content(PIC),and Shannon diversity index(I)was 22.39,0.74,0.86,and 1.66,respectively,indicating that the genetic diversity of T.wallichiana var.mairei is higher.Among them,the Fenyi population has the highest genetic diversity,so the population should be given priority consideration when determining priority protection units.The analysis of molecular variance showed that the genetic variation mainly existed in the population(84.90%),and the variation among populations accounted for 15.10%(P<0.001),indicating that the genetic differentiation of natural populations of T.wallichiana var.mairei was lower,and the gene flow(1.62)high.Based on the UPGMA method,18 populations were grouped into 4 groups.Mantel test showed that the genetic distances between populations were not significantly correlated with geographical distances and altitudes.(3)Family variation and selection of growth and branching traits of T.wallichiana var.maireiThe genetic test results of the 5-year-old T.wallichiana var.mairei superior tree family test forests showed that the differences between growth and branching traits reached extremely significant levels.There were obvious family × site interaction effects in the traits of tree height and primary branch number,but the interaction effects of other traits were not significant.All growth traits in the T.wallichiana var.mairei families were present very significant positive correlation.The heritability of tree height traits was 0.69～0.87,and the heritability of each plant was 0.39～0.79,indicating that the growth of its was controlled by moderate to strong genetic.Taking tree height as the main selective trait and comprehensive branching habit,10 excellent families were selected initially.