Chang-Ho Eun

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.

Satsuma mandarin (Citrus unshiu Marc. cv. Miyagawa-wase) is the most widely cultivated citrus variety in Korea. Although most varieties are imported from Japan, efforts have focused on developing new domestic varieties. We produced mutants by irradiating C. unshiu Marc. cv. Miyagawa-wase scions with gamma rays and grafting them onto C. unshiu Marc. cv. Miyagawa-wase branches. We compared the characteristics of these mutants with Miyagawa-wase fruit as a control. A mutant line named Jedae-unshiu with a unique fruit shape was selected for investigation in detail. The phenotype of Jedae-unshiu fruit demonstrated vertical troughs on the flavedo, smooth albedo without rough protruding fibers, and good adhesion between peel and flesh. In addition, Jedae-unshiu had thicker peels and higher fruit hardness than the control. Higher levels of hesperetin and narirutin, representative flavonoids, accumulated in the peel and flesh of Jedae-unshiu than those of the control. Cellular-level microscopic observations of the mature fruit peels demonstrated epidermal cell disruption in the control but not in Jedae-unshiu. Our results suggest that Jedae-unshiu has high possibility for development as a good storage variety containing large amounts of flavonoids, in addition to potential for ornamental value due to the unique shape of the fruit.

Citrus fruits are rich sources of different phytochemicals for human health due to their high anti-oxidant capacity. However, the anti-aging effect of citrus fruits has not been well understood. In this study, methanol extracts taken at various developmental stages from tissues of Citrus unshiu was used to investigate its anti-aging effect by an elastase/collagenase inhibition assay, and a gas chromatography-mass spectrometry (GC-MS) analysis was carried out to identify the potential anti-aging compositions. The elastase/collagenase inhibitory activity was greatest in the flesh of immature green fruit (i.e., early July flesh (EJF)), and four candidate compounds were selected by GC-MS and evaluated by a collagenase inhibition assay. Three of the four candidate compounds (heptadecanoic acid, D-allose, and 5-hydroxymethyl-2-furaldehyde (HMF)) showed anti-aging activity, and the activity was highest in heptadecanoic acid, followed by D-allose and HMF. The total phenolic content (TPC), total flavonoid content (TFC), and anti-oxidant activity (DPPH and ferric reducing anti-oxidant power (FRAP) assay) were also investigated. Interestingly, the patterns of the total phenolic/flavonoid content and the anti-oxidant activity were different from that of the elastase/collagenase inhibitory activity. Flowers had the most anti-oxidant activity followed by immature fruit, and the fruit peels had more anti-oxidant activity than its flesh at all stages of development. This study demonstrated that the flesh of immature fruit and flowers of C. unshiu could be sources of anti-aging and anti-oxidant agents for human health, respectively.