Genotyping by sequencing 
Genomic DNA was extracted from floral buds using Qiagen DNeasy Plant Mini Kit (QIAGEN Strasse 1, 40724 Hilden, Germany) following the manufacture’s instruction. Samples were sent to the Institute of Genomic Diversity at Cornell University for genotyping by sequencing, libraries were prepared as described in the pro­tocol by Elshire et al. (2011). Briefly, the DNAs from 96 individuals were digested with EcoT22I 6-base cutter (ATGCAT) to reduce the genome complexity. A 96-plex GBS library comprising 95 DNA samples and a negative (no DNA) were prepared by ligating the digested DNA to unique barcode nucleotide adapters, followed by standard PCR. The resulting 96-plex library was sequenced on a single lane of an Illumina HiSeq 1 x 100bp.