Research On The Genetic Diversity And Phylogenetic Relationship Of Loose Skin Mandarins (Citrus Reticulate Blanco)

Wild mandarins played important roles both in caltivar breeding and citrus phylogenetic relationship analysis. In the first chapter of this thesis, genetic diversity of mandarin accessions and phylogenetic relationships among them and related citrus species were studied. Hongjiangcheng is a valuable cutivar in China, and as a citrus synthetic chimera, in the second chapter of this thesis, its genetic background were studied. The main results were as follows:1. In the genetic diversity study of 33 loose skin mandarin landraces and 19 wild mandarin accessions, ten nuclear simple sequence repeat(nSSR) and eight chloroplast simple sequence repeat(cpSSR) markers were seleted as polymorphic markers. These primers amplified 60 nuclear SSR polymorphic bands and 19 choloroplast SSR polymorphic bands. Except for accessions in 3 groups formed by 7 accessions, nuclear SSR primers could discriminated all accessions studied, even two differently distributed'Shatangju' accessions.2. Our analysis of nuclear and chloroplast genome polymorphism showed that the genetic diversity in wild accessions was slightly higher than that found in landraces, with polymorphic information content values of 0.6138 and 0.5091 at nSSR loci, and 0.4921 and 0.3769 at cpSSR loci, respectively.3. Five groups of landrace and two groups of wild mandarin were identified based on the nSSR data and two groups each of landraces and wild mandarins were identified at the cpSSR loci. Different distribution patterns of landraces and wild mandarins were observed between dendrograms constructed using these two marker systems, and hybrid origins of several landraces were suggested by these results. Combined analysis also suggested that, among wild mandarin,'Chongyi' showed the closest relationship to landraces, and that'Chazhigan' landrace was the primary genotype among landraces.4. Of the 1157 aligned positions in the trnL-trnF regions, 94 sites were variable, pairwise sequence divergences ranged from 0 to 2.8%. Of the 1556 aligned positions in the matK regions, 136 sites were variable, pairwise sequence divergences ranged from 0 to 2.6%. Of the 795 aligned positions in the Flint2 region, 91 were variable, pairwise divergence ranged from 0 to 3.4%. 5. Compatibility analysis of three DNA sequence dataset showed difference among three dataset. Therefore, maximum parsimony, maximum likelihood and neighbor join distance phylogenetic trees were constructed using three dataset sperately and using combinated dataset of trnL-trnF and matK sequence dataset. Incompatiablity between nuclear DNA sequence dataset and chloroplast DNA sequence dataset were used to analysize hybrid origination of related accessions.6. Sequence data showed that most of landraces and most of wild accessions form a manophyletic clade. Among other landraces,'Choupigan','Huapigan','Kuigan','Bendiguangju' and'Ougan' were of hybrid orign with mandrin as male parent and pummelo or orange as female parent; Qingpi is a variety of Yuzu(Citrus junos Sieb. Ex Tanaka). Two other wild accessions,'Mangshan wild mandarin Al' and'Daoxian wild mandarin No. 5' were sister to loose skin mandarin clade.'Mangshan wild mandarin B0','Jangyong wild mandarin No. 4' was sister to landraces in loose skin mandarin clade.'Daoxian wild mandarin No. 1','Chongyi wild mandarin Al','Jiangyong wild mandarin No. 1' and'Chongyi wild mandarin A2' formed a clade in loose skin mandarin clade.7. Several genotypes related to mandarin were also discussed in this thesis, and their possible paternal and mathernal origins were also proposed. Two kinds of pepada were identified according their phylogenetic relationships to species of genera Citrus. No phylogenetic relationships were found between calamadin and loose skin mandarin.8. In addition, SSR and RAPD molecular markers were employed to study chimerism of five'Hongjiangcheng' chimeras. One pair of cpSSR primers and one RAPD primer amplified polymorhic bands in five materials, and the distribution of polymorhic bands could be explained by chimera itselves. One polymorhic RAPDs was sequenced, and results showed that it was 61.9% homologous to Poncirus trifoliata citrus tristeza virus resistance gene locus.