Studies On Phylogenetic Analysis Of Pyrus L.and Evolution Of East Asian Pear Cultivar Goups Based On Non-coding CpDNA Regions

The genus Pyrus L. belongs to the subfamily Pomoideae (Maloideae) and the family Rosaceae. There are about20primary species in Pyrus, and13species originating from China have been classified and extensively accepted by Chinese botanical taxonomists. The commercial pear cultivars native to East Asia are composed of five groups:Ussurian pear (UP), Chinese white pear (CWP), Chinese sand pear (CSP), Xinjiang pear (XP), and Japanese pear (JP). Because of lack of discriminated morphological traits among Pyrus species, the phylogenetic relationship among Pyrus species and the evolution of East Asian pear cultivar goups have been a long-standing difficult problem based on morphology. The traditional methods including chemical compounds, pollen ultrastructure and isozymic patterns have been used to distinguish pear species and cultivars. However, these markers are quite number-limited and some are vulnerable to environmental influence, the phylogenetic relationship of Pyrus species and the evolution of pear cultivar goups are still not well documented.In this study, we tried to elucidate the phylogenetic relationship among Pyrus, understand the evolutionary process of the cultivated pear groups native to East Asia based on non-coding chloroplast DNA regions. The main results were as follows:1:Characterization and phylogenetic utility of non-coding chloroplast DNA regions trnL-trnF and accD-psal in Pyrus.The two non-coding chloroplast DNA regions trnL-trnF and accD-psal of26accessions from19Pyrus species and2outgroup accessions from Malus Mill. were sequenced. A total of36substitutions and11indels were obtained in the combined data. All of the indels were treated as single mutation events and coded as substitutions manually when conducting maximum parsimony and Neighbor Net (NN) analyses. Our results showed that the indels in these two cpDNA regions were reliable phylogenetic characters and increased phylogenetic resolution; Compared with trnL-trnF, accD-psaI evolved quicker and could provide more information for the discovery of inter-and intra-specific relationships in Pyrus. The NN split network indicated that the poor resolution in the phylogenetic tree was partly caused by conflicting signals or by lack of sufficient informative sites. In addition, maternal lineages of putative inter-specific hybrids were revealed.2:Evolution of cultivated pear groups native to East Asian based on accD-psaI haplotypes.A total of339accessions (mainly local cultivars) including96CWP,177CSP,18UP,3wild types of P. pyrifolia from21provinces in China and45JP were used to amplify and sequence accD-psaI regions. As a result,9haplotypes were identified (Hapl-Hap9). Except Hap3and Hap7, other haplotypes could be found among accessions of Pyrus species. We suspected that accD-psaI haplotypes in Pyrus were fixed before the cultivar evolution. The distribution pattern of haplotypes existed in all accessions were formed through artificial spread of germplasm with different haplotypes from the diversity center to other places.There were3major haplotypes (Hap1, Hap2and Hap3) in cultivated pears. They belonged to two different evolution lineages which all started from the ancestor haplotpe (Hap5):Hap5-Hap4-Hap3、Hap5-Hap2-Hap1. There were the most plentiful haplotypes in Southwestern China. Proportion of Hap2and Hap3decreased from Southwest to East and North China, while that of Hapl increased. The results above suggested cultivated Chinese sand pears were originated from Southwest China. The rare haplotypes were lost gradually and most evolved haplotype (Hapl) was retained during the spread of Chinese sand pears. Chinese sand pears occupied the most number of haplotypes and the CWP was just a subset of CSP. AMOVA analysis of all cultivated pear group revealed that there was no genetic differentiation between CSP and CWP. Molecule evidences in this study could not support that CWP was treated as an independent species, andso called CWP cultvars might be evolved from P. pyrifolia in different geographical ranges along with its migration. The composition of JP’s haplotypes was much similar to that of the cultivars from Zhejiang and Fujian Provinces. So we speculated that the cultivars of JP might be derived from the sand pears in Zhejiang and Fujian Provinces.