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.
Freezing temperatures cause different levels of freezing injury and change biochemical components of trees. In this study, the range of survival temperature and variation in electrolyte leakage, and in concentrations of sugar, starch, and proline were determined in peach twigs (Jinmi, Changhowonhwangdo, and Kawanakajima Hakuto) exposed to artificially controlled freezing temperature. Freezing temperatures at which the plants were damaged by stress were found to be −21˚C in Jan. and Feb., −18˚C in Mar., and −6˚C in Apr. Electrolyte leakage increased as temperature decreased from −15˚C to −24˚C at each assessment time. Sugar gradually decreased after the endodormancy period in the late part of winter, and sugar concentration was overall lower in freezing temperature treatments, while starch increased as a result of changing seasons from Jan. to Apr. The trend of proline concentration was related to the survival rate of peach trees during winter. This study suggests possible safe temperatures for survival and cultivation of peach trees as well as identifying freezing temperature effects on internal components of freeze-injured peach twigs.
Being self-incompatible, most Asian plums should be planted with a compatible pollinizer to produce fruits. Therefore, the selection of an adequate pollinizer is essential when new plum cultivars are released. To select a suitable pollinizer for ‘Summer Fantasia’ plum, the S genotype, cross-compatibility, pollen viability, and flowering time of five candidate cultivars were evaluated. Using polymerase chain reaction (PCR) analysis, the S genotype of ‘Summer Fantasia’ was determined as SaSc, which was expected to be compatible with other S genotypes. To test cross-compatibility, the trees were covered with caging net to prevent unintended pollination, and pistils were hand pollinated without emasculation. Fruit set percentage was calculated 10 weeks after pollination. The fruit set percentage resulting from the cross between ‘Summer Fantasia’ and ‘Taiyo’ (SbSc) was 13.8%, whereas that resulting from other combinations was less than 5.0%. Pollen germination percentage was investigated to monitor pollen viability; it varied yearly among cultivars, although ‘Formosa’ (10.6%) and ‘Taiyo’ (13.8%) showed the highest pollen germination percentages among the cultivars. When averaged over three years and two locations, ‘Summer Fantasia’ bloomed 2–3 days after ‘Akihime’, ‘Formosa’, ‘Oishiwase’, and ‘Purple Queen’. Blooming period of ‘Summer Fantasia’ and ‘Taiyo’ overlapped almost entirely. Overall, the results indicated that ‘Taiyo’ was the most suitable pollinizer for ‘Summer Fantasia’.
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