Assessment of genetic relatedness among cultivars of Pyrus pyrifolia and species native to east Asia by DNA analysis

砂梨与东亚梨属其它种的亲缘关系不明确。日本梨的起源有两种说法：一种是日本梨的发展，另一种是中国中部砂梨的传入。从中国进口的理论具有优势，但日本梨与砂梨的遗传关系尚不清楚，因此尚未得出结论。本研究旨在阐明砂梨与东亚梨属其它种的亲缘关系。我们克隆了与O-甲基转移酶类似的PPOMT 1，它在日本梨和欧洲梨的成熟果实中表达，而在中国梨中没有表达。我们发现该成熟基因在中国梨中缺失，这是梨属分类的一个有用标记。砂梨的一些品种中含有该基因，且与日本梨的序列高度同源。这证实了进口理论。根据ACC合成酶基因（PPACS 1和PPACS 2）对100多个品种的乙烯合成基因型进行了分类。这些信息对于亚洲梨育种策略的制定至关重要。此外，共118梨种和品种原产于东亚进行了RAPD分析。四国地区的部分梨品种与原产于浙江的部分中国梨品种聚为一类。

Genetic relationships of Pyrus pyrifolia and other Pyrus species native to east Asia were ambiguous. The origin of Japanese pear has two theories : 1.Development of Pyrus serotina native to Japan, 2.Imports from Pyrus pyrifolia (Sand pears) native to Central China. The theory for importing from China has an advantage, but the genetic relationship between Japanese pear and sand pear is unclear, therefore, the conclusion has not come yet. The research objective is to clarify the genetic relationships of Pyrus pyrifolia and other Pyrus species native to east Asia. We have cloned PPOMT1, similar t to O-methyltransferase, expressed in ripening fruits of Japanese pear and European pear, not in Chinese pear. We found this ripening gene was deleted in Chinese pear and that this is a useful marker for Pyrus classification. A few cultivars of sand pear have this gene and high homology to sequence of Japanese pear. This confirms the import theory. We classified ethylene synthetic genotypes of over 100 cultivars by ACC synthase genes (PPACS1 and PPACS2). This information is critical for making breeding strategies in Asian pears. Moreover, a total of 118 Pyrus spp.and cultivars native to east Asia were subjected to RAPD analysis. Some pear cultivars from Shikoku region were subclustered with some Chinese pears originated in Zhejiang province.