Germplasm Investigation And Evaluation Of Ichange Papeda And Two Indigenous Citrus Species

Citrus distribute widely in our country, and has a long history of cultivation. Wild, semi-wild and indigenous citrus germplasms exist widely in nature. These natural citrus resources have abundant variation and retain plenty of primitive or ancestral genes for the reason that they experienced lower artificial selection pressure. These characters make them be precious materials for citrus phylogenetic systematics and evolution, and the innovation and improvement of germplasms. Two parts included in this study. Part one: germplasm investigation of Ichange papeda and two indigenous citrus germplasms(‘Zhelong Zhoupigan’ and Zhi Que). Part two: the study of genetic diversity and genetic structure of Ichange papeda, and the parental origination of two indigenous citrus germplasms.The analysis of genetic diversity and genetic structure of Ichange papeda:1. The study of genetic diversity used 231 samples from 15 populations showed that 77 pairs of clear and polymorphic n SSR primers were selected. These primers amplified of a total 427 bands with 5.55 bands per locus.2. The study verified that the genetic diversities were high among populations(Na=5.55, He=0.59, I=1.14, PIC=0.54, R=3.31) and low within populations(Na=2.25, He=0.32, I=0.51, PIC=0.26, R=1.93).3. Analysis of molecular variance(AMOVA) showed that the genetic variation both among populations and within populations was high. It was 46.35% and 53.65% respectively. The genetic divergence(Fst) and average gene flow(Nm) were 0.46 and 0.59 respectively, which indicated that there were high level genetic divergence and low level gene flow among Ichange papeda populations.4. Six clusters were obtained from the analyses of STRUCTURE and UPGMA cluster. Population JF and population KM belonged to group A and group B respectively. Two populations origining from Guangxi province formed group C. Group D was constituted of four populations. Population PY, DYC and ZY derived from Guizhou province and population LS from Sichuan province. The rest three were mixed populations, which comprised two of the six groups.5. The Mantel test demonstrated that there were significantly negative correlation between genetic similarity and spatial distance(r=-0.29, P=0.02*). This result meant that the greater the geographic distance, the lower the genetic similarity and greater the genetic distance.6. In the analysis of BOTTLENECK, we concluded that most populations exhibited remarkable heterozygosity excess by both the stepwise mutation model(SMM) and two-phase model(TPM). This result indicated that all these populations deviated from the model of mutations-drift. From the analysis of mode-shift, we knew that all the populations except 7 populations(JF, XS, SS, PY, DYC, ZY, YJ) deviated from L-distribution. It implied that these populations perhaps experienced a recent bottleneck. In other words, the number of effective population size decrease rapidly.7. The analysis of variance(ANOVA) for 8 leaves traits showed that there were highly significant difference both among and within populations. The coefficient of variation in leaf size(leaf length, leaf width, wing leaf length, wing leaf width) was remarkably higher than the value in the leaf shape classes(leaf shape index, wing leaf length/wing leaf width, leaf length/wing leaf length, leaf width/wing leaf width). Four variations of leaf size were 36.75%, 34.48%, 35.85%, 30.91%, and the range of variation in leaf shape classes was 12.97%-14.13%.8. Three clusters were identified based on the analyses of UPGMA and principal component. ClusterⅠwas consisted of two populations(XJC, SS) in which the leaf size was biggest in all 14 populations. Population KM with smallest leaf size constituted cluster Ⅱ. The rest populations constituted cluster Ⅲ, but the 11 populations could not be divided. It was worth mentioning that the classification of clusterⅠand clusterⅡwas the same as the results of n SSR.Parental origination of ‘Zhelong Zhoupigan’ and Zhe Que:1. The analyses of 9 cp SSR markers and 16 n SSR markers showed that ‘Zhelong Zhoupigan’originated from an interspecific hybridization with Citrus sinensis as the female parent and Citrus reticulata as the male parent followed by one or more times backcrosses with Citrus sinensis as the female parent. In addition, another indigenous citrus germplasm Jincheng as the direct female parent was possible.2. From the analyses of 10 cp SSR markers and 16 n SSR markers, we concluded that female parent of Zhi Que was an interspecific hybridization with Citrus grandis descent, and the male parent was Poncirus trifoliate.