*4.1. Plant Materials*

In early May 2017, fresh leaves were collected from *P. hopeiensis* HB-1, *P. hopeiensis* HB-2, and three local *Pyrus* species, *P. ussuriensis* Maxin. cv. Jingbaili (which belongs to the *P. ussuriensis* family), *P. communis* L. cv. Early Red Comice (a high-quality variety of Western pear native to the United Kingdom) and *P. betulifolia* (most widely used in northern China as pear rootstocks) in Changli, Hebei Province and were stored before being transported to ORI-GENE Ltd., a science and technology company based in Beijing, China, for chloroplast genome sequencing.
