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Citrus unshiu Marc. cv. Miyagawa-wase is one of the most widely cultivated citrus varieties on Jeju Island in Republic of Korea. Mutation breeding is a useful tool for inducing genetic diversity by causing genomic mutations in a short period of time. We previously conducted mutation breeding using gamma irradiation to develop new varieties of C. unshiu. Here, we describe one of these varieties, Yein-early, which has a redder peel, greater hardness, and higher sugar content compared with the wild type (WT). Yein-early leaves also showed a unique phenotype compared with the WT, characterized by longer longitudinal length, shorter transverse length, stronger curling, and longer petiole length. Genome resequencing of Yein-early and the WT uncovered significant single-nucleotide polymorphisms (SNPs) and insertions/deletions (InDels). These variations were crucial in identifying molecular markers unique to Yein-early. In addition, we developed an allele-specific PCR marker specifically targeting a homozygous SNP in Yein-early that distinguishes it from the WT and other citrus varieties. This study contributes to the understanding of pigment synthesis in fruits and provides a valuable tool for selection of the novel Yein-early variety in citrus breeding programs.

Gamma-ray irradiation is one of the most widely used mutagens worldwide. We previously conducted mutation breeding using gamma irradiation to develop new Citrus unshiu varieties. Among these mutants, Gwonje-early had an ovate shape, a protrusion of the upper part of the fruit, and a large fruit size compared with wild-type (WT) fruits. We investigated the external/internal morphological characteristics and fruit sugar/acid content of Gwonje-early. Additionally, we investigated genome-wide single-nucleotide polymorphisms (SNPs) and insertion/deletion (InDel) variants in Gwonje-early using whole-genome re-sequencing. Functional annotation by Gene Ontology analysis confirmed that InDels were more commonly annotated than SNPs. To identify specific molecular markers for Gwonje-early, allele-specific PCR was performed using homozygous SNPs detected via Gwonje-early genome re-sequencing. The GJ-SNP1 and GJ-SNP4 primer sets were effectively able to distinguish Gwonje-early from the WT and other commercial citrus varieties, demonstrating their use as specific molecular markers for Gwonje-early. These findings also have important implications in terms of intellectual property rights and the variety protection of Gwonje-early. Our results may provide insights into the understanding of morphological traits and the molecular breeding mechanisms of citrus species.