| Tree peonies are one of the most famous flowers in the world but little is known about the origin of cultivated tree peonies (CTP). With the historic, cultural and ornamental values, tree peonies are typical materials fto investigate the origin and evolution of cultivated plants (especially in floricultural crops) and, therefore, become of importantance in academic researches and ornamental application. The study on the relationship between species, all of them endemic to China, and cultivars is an effective way to probe into the origin of CTP and to conserve and utilize the wild germplasm. Paeonia rockii was one of important wild ancestral species involved in the origin of CTP, cultivated flare tree peonies (CFTP) are important composition of CTP and P.×yananensis is a plausible hybrid closely related to CTP, all of which constructured the main contents of this study. Finally, a total of more than six hundred samples, including collections from wild P. rockii throughout the distribution area, CBTP, varieties of P. yananensis and all possible ancestral species, such as P. cathayana, P. ostii, P. jishanensis, P. qiui and P. decomposita were involved in this study using integrated methods such as morphological investigation, chloroplast (cp) DNA gene fragments (petB-petD, rps16-trnQ and psbA-trnH) and fourteen microsatellites to assert the genetic structure of wild P. rockii, the origin of CFTP and hybrid origin of P.yananensis. The results are as follow:1.The genetic structure and diversity of wild P. rockiiThe population genetic structure of P. rockii were distinctly divided into two clades (eastern clade and western clade) as revealed by 3 cpDNA. But based on the microsatellite loci, the population genetic structure were mainly divided into three groups, northern group (NG), eastern group (EG) and western group (WG) in accord with the geographic distribution. The relict populations distributed Ziwuling forestry area in the south to Shan-Gan loess plateau indicated the oldest populations, which moved to south direction driven by cold climatic fluctuations in 1.44(+0.54) milion year ago, and continually moved to eastern and western directions along Qinling Moutation. This could be attributed to integrated factors, such as allopatric fragmentation, climatic fluctuations, lower germinating capacity and ripen rate of seeds, and lack of gene flow among populations, as well as the result of adapted evolution of P. rockii.The haplotypes diversity (Hd,0.8875) based on 3 cpDNA and polymorphism informative content (PIC=0.71) based on 14 microsatellites loci were higher at species level of P. rockii, while Hd based on 3 cpDNA were lower at population level. The genetic differentiation(FST=0.971) between pairwise populations were clearly shown higher as revealed by 3cpDNA. Sixteen haplotypes were found in 20 populations, of which the majority were single, suggesting that the germplasm almost in every population is an exclusive resource that should be more protected from disappearing by strict conservation policies. The analysis of the genetic differentiation based on microsatellites markers were significant, revealing that 67.45% of the total variance was partitioned within populations, whereas 11.32% and 21.22% of the total variance was explained by differences among groups and among populations within groups, respectively.2.The origin of cultivated flare tree peoniesIt were indicated that P. cathayana, P. ostii and P. rockii ssp. atava were three of the most important ancestral species for cultivated blotched tree peonies based on three cpDNA and fourteen SSR data. The former two species served mainly as maternal donation for almost 87.96% of 105 cultivars while the latter was mainly nuclear genome resource as paternal donation for all of CFTP and also as biparently donation for 7.4% of 105 cultivars. P. rockii ssp. rokii nearly was not involved into CFTP, except little relationship with one new cultivar and four tradiational cultivars. Moreover, P. jishanensis, P. qiui and P. decomposita were not directly involved into CFTP. Therefore, it was suggested that CFTP were originated from repeated hybridization and selection at the base of some introduced cultivars of CTP.3.Hybrid origin of P. yananensisOur results showed that P. yananensis as a good morphological species was a hybrid between P. jishanensis as maternal donation grown aroud Wuanhua Mountain in Yan'an City and P. rockii as paternal donation. The case also demonstrated that combined morphological data, cpDNA and SSR were powerful methods for studies on hybrid issues.The study also showed that P. rockii was a paraphyletic species, P. decomposita show close relationship with P. jisahanensis and P. qiui based cpDNA, and also close relationship with western population group of P. rockii ssp. rockii based on SSR. P. cathayana and P. ostii with more close relationship with each other show complicated hybrid background of nuclear genome which was consistent with their status being long cultivated. Moreover, a new chloroplast fragment, petB-petD, and 14 microsatellites were developed for genetic germplasm analysis and identification of cultivated tree peonies.
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