‘Minihyang’ mandarin bears fruits with small size and high sugar content. ‘Minihyang’ mandarin grafted on trifoliate orange (TO) tends to be vigorous and develops water sprout open. It is associated with insufficient floral differentiation and fruit set. Recently, the use of Flying Dragon (FD) as rootstock with a high dwarf effect has been proposed to improve this situation. Therefore, this study was conducted to evaluate the effect of two different rootstock genotypes on tree growth, fruit yield, and fruit quality at the physiological, biochemical, and molecular levels. As a result of the study, in FD, tree vigor was stably maintained, fruit size was large, and the sugar content was high compared to the TO. Fructose, glucose, and sucrose of fruit continued to increase from development to maturity. In particular, fructose and sucrose were significantly higher in the fruits of the FD than those in TO at 150 and 220 days after anthesis. The total sugar content was also significantly higher in the fruit of the FD. The activities of SPS and SS associated with sucrose synthesis tended to be increased during the fruit maturity season, but there was no significant difference between the two rootstocks. On the other hand, the activities of SS and AI breaking down sucrose were high in FD at 150 and 220 days after anthesis. These results suggest that the unloading of sucrose might be increased and affect the sugar content. However, the results of real-time PCR analysis of gene expression related to sucrose metabolism did not show an association with changes in enzyme activity affecting sugar content. Therefore, further detailed studies on the process after the regulation of gene expression are likely to be needed.

Tea, derived from the evergreen shrub Camellia sinensis (L.) O. Kuntze, is one of the most widely consumed beverages globally, playing a significant socioeconomic role in many tropical and subtropical regions. However, tea cultivation is increasingly threatened by climate change, which is affecting growth, yield, and quality. This review explores the current status and prospects of tea plants' responses to climate change. The present study outlines the direct and indirect impacts of climate change including rising temperatures, altered precipitation patterns, and a rise in pest and disease outbreaks, on tea growing regions and tea production. The current study discusses the physiological and biochemical responses of tea plants to climate stressors including temperature stress, water stress and elevated CO 2 levels. It also explores the key adaptive strategies employed by tea farmers, including agricultural practices, breeding and genetic improvement, and pest and disease management. Additionally, the review highlights breeding efforts to develop climate-resilient tea cultivars and the role of traditional and biotechnological approaches in tea plant breeding and genetic improvement. Innovations to mitigate climate impacts on tea plantations such as assessing tea's long-term response to climate change and enhancing tolerance to combined stress conditions are briefly outlined. While progress has been made, significant research gaps remain in understanding the long-term responses of tea plants to climate stressors. Future efforts should focus on continued research, innovation, and collaboration to ensure the sustainability of tea production in a changing climate.

Although colored-leaf tea germplasms can broaden product diversity and functional potential, such resources have been rarely reported in Korea. Herein, we comprehensively characterized Ku2, a newly discovered purple-green line of Camellia sinensis, and benchmarked it against the conventional green-leaf ‘Sangmok’. Five-year-old plants grown under identical open-field conditions were evaluated for growth characteristics, leaf pigmentation, biochemical composition, and antioxidant capacity. Ku2 exhibited a more vigorous growth habit with denser branching and produced leaves that were 11% longer and 17% wider than those of ‘Sangmok’, but chlorophyll concentrations were 29–33% lower. Young shoots of Ku2 in the first flush accumulated markedly higher levels of total polyphenols (+38%), anthocyanins (+78%), and total catechins (+35%), including a 70% increase in epigallocatechin-3-gallate. But amino acid and theanine contents were reduced to 30% and 25% of those in ‘Sangmok’, respectively. Consistent with its polyphenol enrichment, Ku2 extracts displayed superior radical-scavenging activity, with lower DPPH and ABTS IC₅₀ values (7.6 ± 0.5 and 11.6 ± 0.2 µg·mL⁻¹) than ‘Sangmok’ (10.1 ± 0.4 and 15.1 ± 0.1 µg·mL⁻¹), approaching ascorbic acid and Trolox standards. These findings highlight Ku2 as a valuable germplasm for developing premium Korean teas and for breeding colored-leaf cultivars enriched with health-promoting metabolites.

Tea plant [Camellia sinensis (L.) O. Kuntze] is an economically important evergreen crop cultivated worldwide. While most tea plants have green leaves, albino cultivars with yellow or white young leaves have attracted growing interest due to their elevated levels of L-theanine, a key compound that enhances the umami flavor and overall quality of green tea. In this study, we characterized the morphological and biochemical traits of a novel albino tea cultivar, ‘Geumda’, developed in Korea. ‘Geumda’ exhibited yellow young shoots during the first flush and smaller leaves compared to the green-leaf standard cultivar, ‘Sangmok’. Although the catechin content of ‘Geumda’ was lower than that of ‘Sangmok’, it exhibited significantly higher levels of total amino acids, L-theanine, and arginine by 2.1-, 2.0-, and 9.8-fold, respectively. Transmission electron microscopy and gene expression analysis revealed that the elevated amino acid content in ‘Geumda’ was associated with impaired chloroplast development, leading to reduced chlorophyll content and diminished photosynthetic capacity. These findings suggest that ‘Geumda’, with its high concentrations of theanine and arginine and its impaired chloroplast development, represents a valuable genetic resource for the production of functional green teas enriched in umami flavor and beneficial health properties.

This study was conducted to evaluate the effect of different rootstocks on the organic acid content of 'Minihyang' mandarin at different developmental stages. The titratable acidity of 'Minihyang' fruit was the highest in the early stage and decreased rapidly during maturity. The level of acidity in the Flying Dragon rootstock was significantly higher than that in the trifoliate orange rootstock at the early stage of growth, but the difference between them was insignificant during maturity. The content of organic acid showed a similar trend to that of titratable acidity, but the difference between rootstocks was very small. In the early stages of fruit development of 'Minihyang' mandarin, most of the organic acids were citric acid, but during maturation and ripening, malic acid was slightly more than citric acid. Unlike the decrease in citric acid, citrate synthase (CS) activity was maintained at a high level throughout the growing period. On the other hand, with the increase in malic acid, the activities of NAD-malic dehydrogenase (MDH) and NADP-malic enzyme (ME) gradually increased. The expression of CS genes related to citric acid synthesis increased gradually with fruit growth, while the expression of aconitase genes related to decomposition increased gradually. MDH and ME genes related to malic acid and oxalic acid synthesis in mitochondria increased with fruit ripening, while cytoplasmic MDH decreased. In addition, in the expression of phosphoenolpyruvate

Tea (Camellia sinensis (L.) O. Kuntze) quality is shaped by soil, but comparisons among Jeju soil types are lacking. ‘Sangmok’ cuttings were grown for 33 months in three Jeju soils under identical greenhouse conditions—black volcanic ash soil (B-VAS), very dark-brown volcanic ash soil (VDB-VAS), and dark-brown non-volcanic ash soil (DB-NVAS)—and compared for survival, growth, and leaf amino acid and catechin profiles. Volcanic ash soils had more organic matter and nitrogen but less phosphorus and micronutrients than DB-NVAS. Survival (88.9%, 50.0%, and 55.6%; not statistically significant) and height increase (410.9%, 302.2%, and 116.1%) in B-VAS, VDB-VAS, and DB-NVAS were numerically greatest in B-VAS. The final DB-NVAS height-increase value reflects a single surviving plant and should be interpreted with caution. Total amino acids and theanine were 2.6- to 3.6-fold higher in volcanic ash soils than in DB-NVAS, whereas epigallocatechin (EGC) and epicatechin (EC) were higher in DB-NVAS, giving catechin quality index (CQI) values of 3.83, 3.13, and 2.20 and amino acid/catechin (A/C) ratios of 0.31, 0.28, and 0.10. In this pilot planting, survival was numerically highest in B-VAS, and the volcanic ash soils showed greater growth and higher amino acid levels in the pooled shoot samples, whereas the non-volcanic ash soil showed higher catechin accumulation despite weaker growth; these soil-type-level patterns are testable hypotheses for soil-type-informed ‘Sangmok’ cultivation that require confirmation in replicated trials.