ddRAD-seq of Sorbus
For RAD library preparation, purified genomic DNA was digested with the restriction enzymes Mse I and EcoR I (New England Biolabs, Beverly, USA). The resulting DNA fragments were ligated to unique paired-end adapters (P1) and a common adapter (P2), with P1 adapters enabling sample differentiation. Fragments ranging from 300500 bp were selected via electrophoresis on a 2% agarose gel, followed by gel extraction using a Gel Extraction Kit (Omega, Norcross, USA). The selected fragments were amplified by PCR using forward and reverse primers (IGEBIO, Guangzhou, China). RAD libraries were sequenced on an Illumina HiSeq 2500 platform (Jierui Biotech, Guangzhou, China), producing 221 bp paired-end reads.