‘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.

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.

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.