Haploid-resolved and chromosome-scale genome assembly in Citrus unshiu and its parental species, C. nobilis and C. kinokuni

Abstract

Citrus, a member of the Rutaceae family, is a widely cultivated crop with numerous cultivars. In Japan, citrus fruits account for a significant portion of agricultural production. Although several new citrus varieties have been developed through conventional breeding programs, satsuma mandarin remains the dominant cultivar. In this study, chromosome-scale and haploid-resolved reference genome sequences of satsuma mandarin (Citrus unshiu Marc) and its parental varaieties, kishu mandarin (C. kinokuni hort. ex Tanaka) and kunenbo mandarin (C. nobilis Lour. var. kunip Tanaka) were generated using long-read sequencing and Hi-C technologies. The comparison of haploid and unphased genomes revealed structural differences between them, indicating distinct regions in each haploid. In addition, genetic linkage maps were constructed, and genetic and physical distances were compared. The results showed variations in polymorphism density across different regions of the chromosomes. Together, the obtained results provide valuable insights into the genomic characteristics and structural variations of satsuma mandarin and related citrus varieties. These insights will lead to the further elucidation and improvement of citrus cultivars through genome breeding strategies.