Abstract
Recent evidence indicated that interspecific hybridization was the major mode of evolution in Pyrus. The genetic relationships and origins of the Asian pear are still unclear because of frequent hybrid events, fast radial evolution, and lack of informative data. Here, we developed fluorescent sequence-specific amplification polymorphism (SSAP) markers with lots of informative sites and high polymorphism to analyze the population structure among 93 pear accessions, including nearly all species native to Asia. Results of a population structure analysis indicated that nearly all Asian pear species experienced hybridization, and originated from five primitive genepools. Four genepools corresponded to four primary Asian species: P. betulaefolia, P. pashia, P. pyrifolia, and P. ussuriensis. However, cultivars of P. ussuriensis were not monophyletic and introgression occurred from P. pyrifolia. The specific genepool detected in putative hybrids between occidental and oriental pears might be from occidental pears. The remaining species, including P. calleryana, P. xerophila, P. sinkiangensis, P. phaeocarpa, P. hondoensis, and P. hopeiensis in Asia, were inferred to be of hybrid origins and their possible genepools were identified. This study will be of great help for understanding the origin and evolution of Asian pears.
Highlights
The genus Pyrus, with the common name pear, is believed to have originated in the mountainous areas of western and southwestern China [1]
The 93 pear accessions were analyzed for sequence-specific amplification polymorphism (SSAP) using 12 primer combinations, which produced 2,833 fragments varying in size from 70 bp to 500 bp (S1 Table)
In the STRUCTURE results (Fig 2b), these three species were in two genepools, that of the P. pyrifolia and that of the occidental pear. We inferred that these three accessions were the result of hybridization events between occidental and oriental pears. This is the first study on the development of fluorescent SSAP markers based on retrotransposons for the evaluation of the genetic relationships in Asian pears
Summary
The genus Pyrus, with the common name pear, is believed to have originated in the mountainous areas of western and southwestern China [1]. Based on their geographic distribution, Pyrus is divided into two groups: occidental and oriental pears [1,2]. The oriental pears ( referred to as Asian pears) include 12–15 species, the majority being native to China [3]. Based on the geographic distribution, the cultivated P. pyrifolia was further divided into three cultivar groups: Chinese white pear group (sometimes mistakenly assigned as P. bretschneideri Rehd.), Chinese sand pear group and Japanese pear group [3]. Understanding the domestication process of the cultivated pear and the evolutionary process of the pear species will be helpful in exploiting elite genetic resources in pears and aid in modern breeding
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