Abstract The rates of dehardening and rehardening in response to rapid temperature changes in winter are important traits that affect the survival, growth and productivity of the European pear (Pyrus communis [L.]) cultivars in northern countries. The frost hardiness (FH) of shoots of three pear cultivars were studied by a series of freezing tests, after sampling in natural conditions, after dehardening in a growth chamber at 5 °C for 3–4 days (D1) and 16 days (D2), and then after rehardening at −7 °C for 5–7 days (R1 and R2). The FH was assessed by a differential thermal analysis (DTA) to measure the low temperature exotherm (LTE) of shoots, by relative electrolyte leakage (REL) of shoots and by visual damage scoring (VD) of shoots and buds. According to the DTA, the FH of the cultivars varied between −38 °C (‘Conference’ in D2) and −41 °C (‘Pepi’ in R2). The shoots of the cultivar ‘Pepi’ and ‘Conference’ had the highest and the lowest FH, respectively, in all conditions and methods. All the cultivars had the lowest shoot FH after dehardening in either D1 (between −26 °C and −30 °C by REL and between −28 °C and −30 °C by VD) or D2 (between −38 °C and −40 °C by DTA), and the highest FH after rehardening (R1) preceded by D1 (between −30 °C and −34 °C by REL, and between −29 °C and −32 °C by VD). After the dehardening in D1, the buds did not reharden but continued to deharden (the average FH by VD − 24.5 °C). In the forcing conditions, bud growth was resumed most rapidly in ‘Conference’, indicating a shallower dormancy in this cultivar than in ‘Pepi’ or ‘Clara Frijs’. We conclude that the pear cultivars responded to temperature changes in mid-winter, but less than expected, and the responses were similar in all cultivars.

中文翻译：

---

三个欧洲梨（Pyrus community [L.]）品种在隆冬后的芽和芽的再硬化能力

摘要 冬季快速温度变化引起的脱硬和再硬化率是影响欧洲梨（Pyrus community [L.]）品种在北方国家的生存、生长和生产力的重要特征。在自然条件下取样后，在5°C的生长室中脱硬3-4天（D1）和16天（D2）后，通过一系列冷冻试验研究了三个梨品种的芽的抗冻性（FH） )，然后在 -7 °C 下重新硬化 5-7 天（R1 和 R2）。FH 通过差热分析 (DTA) 评估，以测量芽的低温放热 (LTE)，芽的相对电解质泄漏 (REL) 和芽和芽的视觉损伤评分 (VD)。根据 DTA，品种的 FH 在 -38 °C（D2 中的“会议”）和 -41 °C（R2 中的“Pepi”）之间变化。在所有条件和方法中，栽培品种 'Pepi' 和 'Conference' 的枝条分别具有最高和最低的 FH。所有品种在 D1（REL 在 -26°C 和 -30°C 之间，VD 在 -28°C 和 -30°C 之间）或 D2（在 -38°C 和 - DTA 为 40 °C），再硬化后的最高 FH (R1) 在 D1 之前（REL 在 -30 °C 和 -34 °C 之间，VD 在 -29 °C 和 -32 °C 之间）。在 D1 中脱硬后，芽没有再硬化而是继续脱硬（VD 的平均 FH - 24.5 °C）。在强迫条件下，“会议”中的芽生长恢复得最快，表明该品种的休眠期比“佩皮”或“克拉拉·弗里斯”要浅。