Reconsideration on the Origin of Cultivated Pears Native to East Asia Y. Teng K. Tanabe Department of Horticulture Faculty of Agriculture Zhejiang University Tottori University Hangzhou 310029 Tottori 689-5353 P.R. China Japan Keywords: history of cultivation, natural distribution, nomenclature Abstract The commercial pear cultivars native to East Asia are composed of five groups: Ussurian pear, Chinese white pear, Chinese sand pear, Xinjiang pear, and Japanese pear. It has been well known that Ussurian pear cultivars are derived from Pyrus ussuriensis, Chinese sand pear cultivars from P. pyrifolia grown wild in central and southern China. However, the origin of Chinese white pear cultivars and Japanese pear cultivars, and the genetic makeup of Xinjiang pears are still obscure. Chinese taxonomists have assigned cultivars of Chinese white pears to P. bretschneideri. Researchers outside of China speculated that P. bretschneideri might be a natural hybrid between P. betulifolia and cultivated P. pyrifolia, and Chinese white pear cultivars may originate from hybridisation between P. ussuriensis and P. pyrifolia. By means of RAPD analysis, we found RAPD markers specific to P. betulifolia or P. ussuriensis are not present in Chinese white pear cultivars. On the other hand, Chinese white pear cultivars are most closely related to Chinese sand pears based on analyses of RAPD markers, AFLP markers and SSR markers. A new nomenclature for Chinese white pear cultivars has been proposed: P. pyrifolia var. sinensis. As for the origin of native cultivars of Japanese pears, both our study and other researches using different DNA markers infer that at least some Japanese pear cultivars or their progenitors may have been introduced from ancient China and Korea. Xinjiang pears, mainly distributed in northwestern China, have been suspected to be of hybrid origin involving P. communis and Chinese white pears. However, RAPD analysis indicated that at least P. communis, P. armeniacifolia and Chinese white pears or sand pears have been involved in the origin of Xinjiang pears. INTRODUCTION Crop History of Pears in East Asia The pear is one of the most important fruit crops in temperate parts of the world. Pears have been cultivated for thousands of years in the world (Bell, 1991). In East Asia, China has a longest tradition of producing pears and the history of pear culture goes back at least 3000 years (Pu and Wang, 1963; Shen, 1980; Sun et al., 1983). Shi Jing, an ancient Chinese anthology of poetry (1000 BC), mentioned that “pears grow in wet low lands” (Shen, 1980; Sun et al., 1983). Dried pears have unearthed from the tumuli of more than 2000 years ago in Hunan Province and of 1500 years ago in Xinjiang Uygur Autonomous Region, China. The earliest record of pear culture dates back to before 720 in Japan (Kikuchi, 1948). According to ancient Chinese Literature, as early as 2000 years ago, pears had been grown in Korean peninsula (Lee and Hwang, 2002; Yoneyama, 2001). Cultivar development has been continuous in China since early days. According to ancient Chinese literature, as early as 200 BC, Chinese people distinguished cultivated pears from wild species (Kikuchi, 1948; Shen, 1980; Sun et al., 1983). The earliest record of pear cultivars can be found in ancient Chinese book Shi Ji (100 BC). In Qi Min Yao Shu, an ancient agricultural science book written by Jia Sixie in 533-544, 17 cultivars have been recorded. Over long years of culture, different populations of pear cultivars have been developed to adapt to different environmental conditions. There are over 3000 local cultivars of pears distributed in China (Pu and Wang, 1963). Many of the pear cultivars originated hundreds of years ago are still widely cultivated in China. Until recently, Proc. XXVI IHC – IVth Int. Symp. Taxonomy of Cultivated Plants Ed. C.G. Davidson and P. Trehane Acta Hort. 634, ISHS 2004 175 Publication supported by Can. Int. Dev. Agency (CIDA) 200-300 years old pear trees were still grown commercially in some areas of China (Sun et al., 1983). In Shichuan village of Lanzhou City, Gansu Province, one ‘Dongguoli’ pear tree had a trunk circumference of 4.0 m and a height of 12 m and has been estimated to be 350 years old (Teng, unpublished data). In Japan, 200-300 years old pear trees are scattered from the North to the South (Yoneyama, 2001). Taxonomy and Natural Distribution of Pear Species Native to East Asia Pears belong to the genus Pyrus. More than 900 infrageneric nomenclatures of Pyrus have been recorded (http://www.ipni.org), although only about 20 primary species are generally accepted by most taxonomists. According to their original distribution, pears can be arranged into two geographic groups: Occidental pears and Oriental pears (Bailey, 1917). Oriental pears distribute from Tian-Shan and Hindu Kush Mountains eastward to Japan, mainly in East Asia including China, Japan and Korea (Rubtsov, 1944). The modern botanical classification of native pears in East Asia began from the nomenclature of P. pashia Buch.-Ham. ex D. Don. in 1825. However, the taxonomy of pears native to East Asia was confusing and incomplete until 1915, when Rehder identified 12 species native to China. In 1937, the Chinese taxonomist R. Chen cited Rehder’s classification of pears in his book Taxonomy of the Trees in China. Thereafter, based on extensive investi- gation of pear germplasm throughout the country, Yu and Kuan (1963) described five new species. Presently, 13 pear species and a number of varieties are accepted by Chinese botanical taxonomists (Yu and Ku, 1974). It has been generally accepted that four species occur in Japan. In the Korean Peninsula, at least three species can be recognised. Native pear species in East Asia and their geographical distribution are listed in Table 1. Cultivated Pears Native to East Asia Among Pyrus species, only a small number of species have been cultivated for commercial production. Of the Occidental pears, P. communis L. (the common pear) is the major cultivated species and has been widely produced throughout Europe, North and South America and Africa (Bell, 1991). The commercial pear cultivars native to East Asia are composed of five main groups: Ussurian pear (Qiuzili), Chinese white pear (Baili), Chinese sand pear (Shali), Xinjiang pear (Xinjiangli), and Japanese pear (Nashi). The former four types concentrate mainly in China and the last group has distribution in Japan. Besides the major cultivars, the minor cultivars originated from P. ×phaeocarpa Rehder and P. pashia are also grown in some areas of China (Pu and Wang, 1963; Yu, 1979). A few cultivars derived from Pyrus aromatica Kikuchi & Nakai occur in North Japan (Kikuchi, 1948). Traditional cultivars of P. communis are even found in Xinjiang and Gansu Provinces, China (Yuan and Du, 1980). It has been well known that Ussurian pear cultivars are derived from wild P. ussuriensis Maxim. The Ussurian pears are the coldest hardy of all pear cultivars and can endure -40°C to -50°C (Wang, 1996). The fruit of Ussurian pears are usually small globose and oblate with persistent calyx, and become soft and edible after a ripening period, which is clearly different from the crisp flesh texture of Chinese white pears, Chinese sand pears and Japanese pears (Table 2). The leaf morphology of Ussurian pears is also distinguished from that of other types of cultivars (Table 2). Chinese sand pears, P. pyrifolia (Burm. f.) Nakai, distribute in central and southern China, and bear fruit with smooth or russet skin. The shape, size and shelf life of fruit varies greatly with cultivars (Table 2). The wild P. pyrifolia occurs mainly in the Changjiang (Yangtze) River valley and still can be found in some areas of China. Chinese white pear cultivars are the most widely cultivated in China and occupy the most important position in commercial pear production. They grow further south than the Ussurian pears and their geographic distribution is just located between P. ussuriensis and P. pyrif oli a. Therefore, Rubtsov (1944) and Kikuchi (1946) proposed that the origin of Chinese white pears might be involved in hybridisation of P. ussuriensis and P. pyrifolia. Kikuchi (1946) put this group of cultivars under the name of P. ussuriensis var. sinensis Kikuchi. His nomenclature of Chinese white pears has greatly affected many 176 horticulturists in Japan. Many authors in Japan assigned cultivars of Chinese white pears to P. ussuriensis and one of the recent examples can be found in Okubo’s paper (2000). Because of the large difference in morphological characteristics, especially fruit traits between Ussurian pears and white pears (Table 2), Chinese taxonomists and horticulturists have never accepted this nomenclature. On the other hand, since Chen (1937) and Hu (1937) assigned Chinese white pear cultivars to P. ×bretschneideri Rehder, Chinese taxonomists and horticulturists have put Chinese white pear cultivars under the name of P. ×bretschneideri (e.g. Pu and Wang, 1963; Wang, 1996; Yu, 1979; Yu and Ku, 1974; Yuan and Du, 1980). Rehder (1915) named P. ×bretschneideri to refer those pears growing in North Hebei Province, which were suspected to be a hybrid between P. betulifolia Bunge and large-fruited cultivars (P. pyrifolia?) (Kikuchi, 1946). Kikuchi’s view about P. ×bretschneideri has been cited by other scholars such as Challice and Westwood (1973) and Bell (1991). Therefore, the relationship between Chinese white pear cultivars and P. ×bretschneideri is still to be solved. Japanese pears have been considered to be the same germplasm as Chinese sand pears and grouped into P. pyrifolia. The morphological characteristics of Japanese pear cultivars are similar to those of Chinese sand pears (Table 2). As for the origin of Japanese pear cultivars, the generally accepted opinion is that this group of cultivars have been domesticated from wild P.