Genomic DNA extraction and library construction
The whole genomic DNA was extracted from frozen young leaves according to the CTAB method (Yu et al. , 2019). The p-pool and g-pool representing buds turning purple and buds keeping green samples, respectively, were constructed by collecting 30 BC2F2 individuals in each pool. DNA quality was detected, and their concentration was quantified by electrophoresis on 0.8% agarose gel and a spectrophotometer (NanoDrop, United States), respectively. Sequencing libraries were constructed according to the instruction of the TruSeq DNA PCR-free prep kit (Illumina). The quality of libraries was tested using Agilent High Sensitive DNA kit by Agilent Bioanalyzer, and the qualified libraries were sequenced by the Illumina NovaSeq platform. The raw sequencing data were filtered using fastp (v0.20.0) to discard those reads with low quality.