Phylogenetic Relationship Among The Speices Of Sect. Moutan And Origin Of Cultivated Tree Peony

Tree peony, being crowned the title "King of Flowers" in China. The cultivated tree peonies have been used as medicine for over 2,000 years in China and 500 years in Europe, respectively, and now cultivated all over China and the temperate regions of the world for their medicinal, ornamental, and economic values. Therefore, to clarify the phylogenetic relationships among wild species and origin of cultivated tree peonies have the important both theoretical and practical value.1. Phylogenetic relationships among wild species of section MoutanTree peony belongs to the section Moutan DC. of the genus Paeonia L. (Paeoniaceae). In addition to this woody group, there are two herbaceous sections in this genus, Sect. Paeonia and Sect. Onaepia. The genus Paeonia consists of more than 30 species, distributed widely in the temperate region of the world. The section Onaepia has only two species endemic to North America, whereas Sect. Paeonia comprises about 22 species found in Europe, North-west Africa and Asia spreading from Portugal and Morocco to Japan. The sect. Moutan, following a recent classification system of Hong & Pan, contains eight species and three of them each have two subspecies, distributed in southwestern, central and northern region of China.In the past decade, important progress has been made in the taxonomy of tree peony. However, although the interspecific relationships of wild tree peonies have been previously investigated using morphological data, molecular marker, and DNA sequences of different genomes, the species phylogeny of the Sect. Moutan is still poorly understood.In the present study, the phylogeny of the wild tree peony species (Section Moutan DC, Paeonia, Paeoniaceae), represented by twelve accessions collected from all eight species in the section, was investigated based on the DNA sequence in five DNA fragments from both nuclear (Adh1A, Adh2 and GPAT) and chloroplast (trnS-trnG and rps16-trnQ) genomes, as well as morphological characters. Both maximum parsimony (MP) and Bayesian inference of phylogeny (BI) trees were reconstructed based on the combined data of the DNA sequences and morphological data, respectively. The MP and BI trees have the similar topology, and on the gene tree the sect. Moutan clearly branched into two clades. One consists of two species, P. delavayi and P. ludlowii, corresponding to the Subsect. Delavayanae, and another is composed of six species, corresponding to the Subsect. Vaginatae of Stern's system. Within the second clade, the six species can be divided into three subclades consisting of P. rockii and P. decomposita, P. jishanensis and P. qiui, P. suffruticosa and P. ostii species-pairs, respectively. According to these results, the following interspecific relationships among species in the Sect. Moutan were inferred: 1) P. ludlowii and P. delavayi are the most closely related species in the Sect. Moutan; 2) P. decomposita is most closely related to P. rockii, P. jishanensis is closely related to P. qiui, and P. suffruticosa is closely related to P. ostii; 3) P. jishanensis / P. qiui species-pair is more closely related to P. ostii / P. suffruticosa species-pair than either of them to P. decomposita / P. rockii species-pair. These results provide up to date the clearest picture of the phylogeny of wild tree peony species in the Sect. Moutan.2. Origin of cultivated tree peoniesTree peony is a widely favored flower over the world. Based on available reference, cultivated tree peonies have appeared nearly 2000 years ago, and transferred to Europe for 500 years. After several thousands years breeding, cultivated tree peonies have nearly more than one thousand strains derived from few traditional strains, and strains in different regions with particular characters. Based on the geography, cultivated tree peonies can be divided into four strain groups, Central group, northwest group, Southern group, and Southwest group. The origin of cultivated tree peonies includes four aspects: 1) the relatives of cultivated tree peonies from wild species; 2) the earliest time of people try to cultivate tree peonies; 3) the earliest place of people try to cultivate tree peonies; 4) the pattern and mechanism of origin and evolution of cultivated tree peonies. The first question we wish to address is what is the difference between cultivated tree peonies and wild species? In morphological character, the number and color of petal is more diverse. Cytological analysis suggested the number and other characters of chromosome are similar among the wild species and different strains of cultivated tree peonies. The second question is how the traditional cultivated tree peonies origin, single species and single place or multiple species and multiple places, just simple domestication or hybrid, if hybrid is related with the origin of cultivated tree peonies, then how many wild species are involved? The previous researches suggested, traditional cultivated tree peonies are come from various pathways, namely, domestication of wild species, hybrid between wild species and cultivated tree peonies, hybrid among different strains of cultivated tree peonies. But the available data are focus on the analysis of ancestral reference, morphological, and cytological, there are no any work has been done based on molecular marker.In the present study, 12 accessions represent 8 wild speices, 95 accessions represent four major strain groups. We sequenced all the samples trnS-G and rps16-trnQ sequence, and sequenced GPAT sequence from 8 wild species and 37 strains. Based on these data, we used MJ (Medium-Jioning) method implemented in Network (version 4.2) and PAUP* (version 4.0) to reconstruct the network and phylogenetic tree. We analyzed the origin of cultivated tree peonies based on the above results. Finally, we found that the four strain groups originated from different wild species independently. 1) Some strains of Central group directly domesticated from P. suffruticosa distributed in Henan province, others originated by hybridization of two or multiple wild species from P. suffruticosa, P. ostii, P. jishanensis, P. qiui, P. rockii; within Southern group, the cultivated tree peonies of Qin dynasty was domesticated from P. ostii or P. suffruticosa in Anhui, other strains are originated from hybridization of P. ostii or P. suffruticosa in Anhui with P. suffruticosa in Henan; northwest group originated from hybridization of P. suffruticosa in Henan with P. rockii; Southwest group is similar to central group, which has a complicated genetic basis, originated from two or multiple wild species, but the wild species distributed in southwest are not involved, this suggests southwest group are mainly originated from introduction or domestication of strains within other strain groups. Based on the distribution of wild species and the origin time of cultivated tree peonies, cultivated tree peonies related with P. decomposita and P. delavayi are originated recently, therefore, the traditional cultivated tree peonies are mainly derived from P. suffruticosa, P. ostii, P. jishanensis, P. qiui, P. rockii. Among them, P. suffruticosa from Henan is the important, which is the maternal part of four strain groups. Our results support the opinion of Li Jia-Jue: originated multiple place, multiple species.