DISCUSSION
We report the first assembly of a high-quality, chromosome-level genome for Chinese walnut using a combination of Illumina HiSeq X Ten, Nonopore, and Hi-C sequencing platforms. Compared to previously available genome assemblies for this species, the Scaffold N50 value was improved 163 fold (contig N50 size of J. cathayensis v2.0 was 23,789,296 bp versus 145,095 bp contig N50 size for J. cathayensis v1.0), and the final calculated genome size is smaller (580Mb, v1.0 versus 548Mb, v2.0) (Figure1; Table S12). Through Hi-C, a chromosome-level genome was obtained with a scaffold size of 36Mb (Table S12) and scaffolds resolved into 16 chromosomes, unlike the previously available genome (J. cathayensis v1.0; Stevens et al., 2018) (Table S5, Table S12) (DeMaere & Darling, 2019; Zhang et al., 2020c; Chen et al., 2020; Choi et al., 2020). We predicted 29,032 protein-coding genes from the generated assembly. The phylogenetic tree revealed that Chinese walnut and Persian walnut diverged ~4.6 million years ago. This high-quality chromosome-level genome will be benefit for breeding and genetic variation discovery in walnut (Juglans ) species.