Abstract
Asian pear plays an important role in the world pear industry, accounting for over 70% of world total production volume. Commercial Asian pear production relies on four major pear cultivar groups, Japanese pear (JP), Chinese white pear (CWP), Chinese sand pear (CSP), and Ussurian pear (UP), but their origins remain controversial. We estimated the genetic diversity levels and structures in a large sample of existing local cultivars to investigate the origins of Asian pears using twenty-five genome-covering nuclear microsatellite (simple sequence repeats, nSSR) markers and two non-coding chloroplast DNA (cpDNA) regions (trnL-trnF and accD-psaI). High levels of genetic diversity were detected for both nSSRs (HE = 0.744) and cpDNAs (Hd = 0.792). The major variation was found within geographic populations of cultivated pear groups, demonstrating a close relationship among cultivar groups. CSPs showed a greater genetic diversity than CWPs and JPs, and lowest levels of genetic differentiation were detected among them. Phylogeographical analyses indicated that the CSP, CWP, and JP were derived from the same progenitor of Pyrus pyrifolia in China. A dissemination route of cultivated P. pyrifolia estimated by approximate Bayesian computation suggested that cultivated P. pyrifolia from the Middle Yangtze River Valley area contributed the major genetic resources to the cultivars, excluding those of southwestern China. Three major genetic groups of cultivated Pyrus pyrifolia were revealed using nSSRs and a Bayesian statistical inference: (a) JPs; (b) cultivars from South-Central China northward to northeastern China, covering the main pear production area in China; (c) cultivars from southwestern China to southeastern China, including Yunnan, Guizhou, Guangdong, Guangxi, and Fujian Provinces. This reflected the synergistic effects of ecogeographical factors and human selection during cultivar spread and improvement. The analyses indicated that UP cultivars might be originated from the interspecific hybridization of wild Pyrus ussuriensis with cultivated Pyrus pyrifolia. The combination of uniparental DNA sequences and nuclear markers give us a better understanding of origins and genetic relationships for Asian pear groups and will be beneficial for the future improvement of Asian pear cultivars.
Highlights
Pear (Pyrus L.), as an important temperate fruit tree worldwide, has been cultivated for more than 3,000 years (Pu and Wang, 1963; Janick, 2000)
Analysis of molecular variance based on nuclear loci containing simple sequence repeats (nSSRs) data was analyzed for pear cultivars and wild P. ussuriensis accessions native to East Asia (Supplementary Table S3)
More than 400 local pear cultivars were collected across the main pear distribution areas of China and Japan (Supplementary Table S1), and used in the genetic analysis
Summary
Pear (Pyrus L.), as an important temperate fruit tree worldwide, has been cultivated for more than 3,000 years (Pu and Wang, 1963; Janick, 2000). Pyrus species are naturally distributed in the Eurasian continent and are geographically divided into two native groups: occidental and oriental pears (Bailey, 1917). The occidental pears, including over 20 species, occur in Europe, Northern Africa, Asia Minor, Iran, Central Asia, and Afghanistan, and the majority of cultivars in these areas originated from Pyrus communis L. The oriental pears, comprising 12–15 species, are distributed from the Tian Shan and Hindu Kush Mountains eastward to Japan and are largely concentrated in East Asia, including China, Japan, and Korea (Rubtsov, 1944; Challice and Westwood, 1973). Asian pears account for over 70% of the worldwide total in terms of both production volume and cultivated area (FAO)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
