‘Inchangkyool’ varieties, which are believed to have been cultivated in Jeju for a long time, have leaves and flowers with a lemon-like fragrance. They have been suggested to be given the same scientific name as Citrus ichangensis, which is known to originate from China’s Southwest and Midwest regions. However, the genetic characterization of ‘Inchangkyool’ has not been reported, and literature is not readily available. Hence, in this study, 30 citrus chloroplast (cp)DNA (trnL-trnF) regions and nuclear ribosomal DNA internal transcribed spacer (ITS) regions were tested to identify the genetic relationship between ‘Inchangkyool’ and C. ichangensis and the origin of ‘Inchangkyool’ cultivars. Our results indicated that the total nucleotide sequence length of the trnL-trnF intergenic spacer (IGS) region and the G + C content was 373 bp and 36.73%, respectively, in the cpDNA of C. ichangensis and ‘Inchangkyool’, whereas the ITS1 regions were 247 and 248 bp and the ITS2 regions were 228 and 226 bp, respectively. Furthermore, the sequence lengths of the total ITS (ITS1 + 5.8S rDNA + ITS2) regions were 638 and 637 bp, respectively, whereas the G+C content was 70.16%, 71.26%, 69.03%, 70.61%, 64.6%, and 65.49%, respectively - showing differences in the nuclear ribosomal DNA region. However, the nucleotide sequence length of the 5.8S rDNA region was 163 bp and the G + C content was 54.6%, which were the same for both varieties. In addition, sequence divergence and phylogenetic analysis of the trnL-trnF and ITS regions in chloroplast DNA showed that the sequence divergence of the trnL-trnF region on the chloroplast was 0–0.008. This result indicates that ‘Inchangkyool’ is most closely related to Jeju eight native citrus cultivars including ‘Dongjeongkyool’. It is also closely related to C. ichangensis cultivars and six common citrus cultivars. In other words, the ‘Inchangkyool’ cultivar was inherited from the same maternal line as the Chinese C. ichangensis. The divergence values of the nuclear ribosomal DNA region between ‘Inchangkyool’ and ‘Dongjeongkyool’ and C. ichangensis were 0.008 and 0.026, respectively. These results indicated that ‘Inchangkyool’ was most closely related to ‘Dongjeongkyool’, and was farther from the C. ichangensis cultivar. In addition, phylogenetic relationships found ‘Inchangkyool’ to belong to the same group as the ‘Dongjeongkyool’ cultivar of jeju native citrus cultivars and a different group from C. ichangensis. From the above results, it is suggested that ‘Inchangkyool’ cultivar has been classified from the same maternal cultivar as the C. ichangensis in China, but has been obtained through long-term crossing with the same species as ‘Dongjeongkyool’. Moreover, based on the above results, it is believed that a distinct cultivar name for ‘Inchangkyool’ can be presented.

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Although small-scaled breeding programs for apples, pears, and grapes were conducted in the 1930s and 1940s, national fruit breeding programs by the Korean government were commenced after the foundation of the National Horticultural Technical Institute on May 20, 1953, and the programs were confined to apples and pears. Peach and grape breeding programs were started after the establishment of Rural Development Administration (RDA), with the Horticultural Experiment Station as its affiliated research organization in 1962. However, because of insufficiencies in breeding infrastructure, manpower, and funds during the 1960s and 1970s, most efforts were devoted to the collection and selection of wild Akebia and Actinidia, local varieties of astringent persimmons, jujube, and apricot, and adaptability tests of foreign fruit varieties. Fruit breeding programs became more activate with the establishment of the Apple Research Institute, the Pear Research Institute and the Citrus Research Institute as subsidiary organizations of the Fruit Research Institute, RDA, in 1991, and with Fruit Experiment Stations for grapes, persimmons, and peaches as affiliated provincial research organizations in early 1990s to cope with the domestic agricultural market opened by Uruguay Round Agreements. The legislation of the Seed Industry Law in 1995 and joining the UPOV in 2002 contributed to fruit breeding activation in the private sector. The results of such breeding programs include the development of the ‘Danbae’ pear as the first fruit variety in 1967, the ‘Yumyong’ peach in 1977, the ‘Hongro’ apple, and the ‘Cheongsoo’ grape. After the Korea-Chile FTA, effective in 2004, research projects for the development of molecular markers linked to disease resistance in fruit trees and seedless grapes have been carried out to improve the competitiveness of the Korean fruit industry. However, the establishment of a molecular breeding system based on genome sequence information and collaboration among research organizations are required for competition in domestic and foreign fresh fruit markets. In this review, we analyze the achievement from the fruit breeding programs operated by central and local autonomous governments since 1945, and propose future directions and strategies.

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A new citrus cultivar ‘Tamdosamho’ is a hybrid obtained from a cross of ‘Kiyomi’ (Citrus unshiu×Citrus sinensis, the seed parent) and ‘Sunburst’ (Citrus reticulate, the pollen parent) at the Citrus Research Institute of the National Institute of Horticultural and Herbal Science in 2004. ‘Tamdosamho’ had the first fruit set in 2010 and field evaluation has been conducted until 2012. The tree of ‘Tamdosamho’ was vigorous and had a lot of fruit bearing. The average fruit weight was 230g and its shape was flatten-oblate with a little neck. The fruit peel color was dark orange, and peel coloration began in mid-October and fully developed in early December. The fruit matured in mid-February from cultivation under plastic film house. Total soluble solid and acidity of which was 14.0 °Brix and about 1 % respectively. The thickness of the rind was about 2.5 mm on average and was thinner than that of satsuma mandarin (Citrus unshiu), so removing the peel was easy. This cultivar had characteristic of self-incompatibility and parthenocarpy and didn’t bear seeds from monoculture but if it be fertilized by the pollen of other cultivars could be seedy. In the case of cultivation in the open field, the fruits could be damaged by cold temperature and then ‘Tamdosamho’ is recommended for cultivation under plastic film house. (Variety registration number: 6158)

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A new mandarin hybrid cultivar ‘Shinyegam’ was developed from a cross between ‘Kiyomi’ (Citrus unshiu × C. sinensis) and ‘Wilking’ (Citrus reticulata) at the Citrus Research Institute of the National Institute of Horticultural and Herbal Science in 2012. The ‘Jegam na No. 33’, a first selection seedling from the fruits obtained in 2008 was finally named ‘Shinyegam’ after field evaluation trials at five locations in Jeju island, Korea from 2010 to 2012. The tree vigor was intermediate and the tree was spreading in nature, similar to that of the ‘Kiyomi’ cultivar. The fruits produced were compressed to oblate and globose in shape, were a deep orange in color, and moderately weighed at 130 g. ‘Shinyegam’ produces fruit that mature in late December, and has few seeds, which are mono-embryonic. The average seed number of a fruit varied depending on the pollinator citrus tree. Cultivation of ‘Shinyegam’ along with the other cultivars possessing high pollen fertility resulted in seed numbers that was more than 20, while in the absence of a pollinator species the seed number was around 5. The fruit contained soluble solids at 11 to 12 ° Bx and the acidity was approximately 1% at maturity. The rind thickness of approximately 2.5 mm ensures easy peeling. The flesh is very tender and juicy, with a pleasant, aromatic flavor similar to that of ‘Wilking’ but is comparatively weak. ‘Shinyegam’ is moderately resistant to the citrus scab disease and melanose, but susceptible to citrus canker. Owing to the high quality of fruit, good aroma, and cold hardness characteristics, this cultivar is expected to satisfy consumer acceptability in terms of the diversity of the cultivar in open-field cultivation.

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The 12 cultivars of the Jeju native Citrus are considered to have originated from China. However, the origin of the cultivar ‘Byungkyool’ (Citrus platymamma Hort. ex Tanaka) is not clearly known. We performed PCR analysis by using three primer sets designed from the internal transcribed spacer (ITS) region of nuclear ribosomal DNA (nrDNA) to analyze the phylogenetic relationship between the traditional citrus cultivars and the Byungkyool cultivar. Sequence length of the nrDNA ITS1 region of JNCPCRI (Jeju Native Citrus platymamma Citrus Research Institute) cultivar was 247 bp, 8the ITS2 region was 228 bp and the total ITS region (ITS1-5.8S-ITS2) was 638 bp. Analysis of the genetic relationship based on the sequence analysis at the ITS region of the JNCPCRI cultivar revealed that the ITS1 region of the cultivar was genetically the same as that of the Byungkyool (JQ990189) cultivar, and the ITS2 region was genetically similar to the Binkyool (JQ990180), Hongkyool (JQ990178), Dangyooja (JQ990179), and Pyunkyool (JQ990181) cultivars. Moreover, the total ITS region in the 5.8S rDNA region was genetically similar to the Hongkyool (JQ990178) cultivar. In addition, the total ITS region of the JNCPCRI cultivar was the most closely related to the Cheongkyool (JQ990183) cultivar and has been reported to originate from the Binkyool (JQ990180) and Pyunkyool (JQ990181) cultivars. Although the JNCPCRI cultivar was morphologically the same as the Byungkyool (JQ990189) cultivar, the ITS region showed genetic heterogeneity. Taken together, we conclude that the genetic variation in the ITS region of JNCPCRI cultivar suggests that it was propagated through fertilization with the surrounding citrus cultivars.

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