Seok Kyu Yun

Assessment of organic acid and sugar composition in apricot, plumcot, plum, and peach during fruit development

Variation in content of organic acids and soluble sugars, and in physical characteristics was evaluated in apricot ( P. armeniaca L. cv. Harcot), plumcot (plum-apricot hybrid, P. salicina ⅹ P. armeniaca L. cv. Harmony), plum ( P. salicina Lindl. cv. Formosa), and peach ( P. persica L. Batsch cv. Jinmi). The content of organic acids and sugars, as well as parameters of fruit quality (weight, dimensions, firmness, total soluble solids, and total acidity) in Prunus fruits during fruit development were determined. Organic acids, including oxalic acid, quinic acid, malic acid, shikimic acid, citric acid, and quinic acid, sugars, including sucrose, fructose, glucose, and sugar alcohol (sorbitol), were identified and quantified using HPLC. Organic acid mostly increased during the early stages of fruit growth (30 - 60 days after full bloom) and decreased until fruits were fully ripened. In general, plum was the highest in most organic acids compared with the other fruits, while apricot contained the lowest acid content except for citric acid. Sucrose, fructose, and glucose content increased with fruit development, unlike content of sorbitol. Plumcot contained the highest fructose, and peach showed the maximum content of sucrose at full maturation stages. Total soluble solids averaged 17.5, 14.8, 11.9, and 10.6 oBrix in apricot, plumcot, plum, and peach, respectively, whereas total acidity was 0.9, 1.4, 0.5, and 0.3% in four Prunus cultivars at ripened stages. Shikimic acid was significantly correlated with oxalic acid in apricot, plumcot, and plum, but not in peach. Fructose and glucose were highly correlated in plumcot, plum, and peach.

Profiling diversity and comparison of Eastern and Western cultivars of Prunus persica based on phenotypic traits

Peach and nectarine cultivars have been released worldwide according to regional preference and local adaptability. However, few reports have provided statistical analyses and comprehensive comparisons of Eastern and Western cultivars. In this study, 22 phenotypic characteristics of 120 peach and nectarine cultivars collected from various countries were examined to determine their diversity and relationships. Based on phenological traits, Western cultivars bloomed earlier than Eastern cultivars, with no difference in ripening time. Fruit shape of Eastern cultivars was close to oblate, while fruit weights were similar. In addition, higher soluble solids concentration (SSC) and lower titratable acidity were observed in Eastern cultivars. In health benefit traits, such as total flavonoid concentration, total phenol concentration, and antioxidant capacity, there was no difference between Eastern and Western type. Positive correlation between chilling unit (CU) and latitude of origin was also found. In addition, the CU was closely associated with flowering date. Relationships among the phenotypic characteristics were also found. Ripening date showed significant and positive correlations with fruit development period, fruit weight, and SSC. In general, cultivars with late ripening times tend to produce high-quality fruit with a sweet taste and large size. The evaluation of a large number of cultivars from various regions with phenotypic variability could provide valuable information on regional preference or local adaptability.

Shoot Growth and Fruit Characteristics of ‘Yumi’ Peach in Response to Side Dressing with Fused Phosphate Fertilizer

This study was carried out to investigate shoot growth and fruit characteristics in 4-year-old ‘Yumi’ peach (Prunus persica) trees in response to various amounts of side dressing with fused phosphate fertilizer (phosphoric acid 17%, FPF) under soil cultivation. The amount of side dressing of FPF was set at 40% of a year’s supply, i.e., 132 g/tree FPF (P2O5 22.4 g/tree) and 22.4 g/tree for the control, 2× (44.9 g/tree), 4× (89.8 g/tree), and 6× (134.6 g/tree), which were supplied via three-split application at 15-day intervals. Shoot length at the fruit maturing stage decreased by 12–16% with increasing amounts of side dressing of FPF up to 6×. The mineral concentration in leaves did not change significantly with increasing levels of FPF. Available P2O5 and Mg contents in soil after fruit harvest were 3.0and 1.8-fold higher under increasing FPF levels (up to 6×) compared to the control, respectively. Leaf SPAD values at the fruit maturing stage decreased with increasing FPF levels, whereas fruit length and width increased with increasing FPF levels. Fruit weights and hardness increased with increasing (up to 6×) amounts of FPF. Finally, free sugar concentrations increased with increasing FPF levels. Therefore, the application of large quantities of FPF via side dressing during early fruit growth can improve fruit quality in ‘Yumi’ peach under soil cultivation. Additional key words: available P2O5, free sugar, fruit enlargement, mineral contents, Prunus persica

Overhead arbor tree shape affects tree development and increases fruit yields in sweet cherry

We evaluated different shapes of sweet cherry trees for their effects on cherry production, and tree development. The tree shapes were a palmette shape (4×7 m), a Y-palmette shape (7×4 m), an open-vase shape (5×4 m), and an overhead arbor shape (6×5 m). After inducing branches on trees of each shape in the first 3 years, tree growth, fruit production, flower bud formation, and labor hours to shape trees were assessed after seven years. The number of new branches was much higher in the overhead arbor shape (10,666 10 a-1) than in the palmette shape (2,867 10 a-1), the Y-palmette shape (6,178 10 a-1), and the open-vase shape (7,250 10 a-1). The average length of new branches was much smaller in the overhead arbor shape (39.6 cm) than in the palmette shape (55.5 cm), the Y-palmette shape (60.6 cm), and the open vase shape (44.0 cm). The results indicate that increasing numbers and decreasing length of new branches are related to tree shape of sweet cherry. Fruit yields were higher 1.86-3.15 times with the overhead arbor shape (916 kg 10 a-1) than with the palmette shape (291 kg 10 a-1), the Y-palmette shape (493 kg 10 a-1), and the open-vase shape (478 kg 10 a-1). A similar trend was observed among the four shapes in the levels of flower bud formation. The lowest amount of labor time was required for developing the open-vase shape (21.9 h 10 a-1) because new branches were not induced artificially in this shape, while the maximum labor time was required to develop overhead arbor shape (47.2 h 10 a-1). The study demonstrated that the overhead arbor shape has potential for small farmers in South Korea.