Changes in Cold Hardiness, Carbohydrate Content, and β-Amylase Gene Expression of Prunus persica during Cold Acclimation and Deacclimation

The present study was performed to confirm differences in cold hardiness, carbohydrate content and β-amylase gene expression during cold acclimation and deacclimation in the shoots of four peach cultivars (cvs. Daewol, Aikawanakajima, Fukuyokabijin, and Kiraranokiwami). During cold acclimation, from September to November 2011, cold hardiness of four cultivars determined by electrolyte leakage analysis dramatically increased. Maximum cold hardiness of four cultivars reached at the end of December 2011; LT₅₀ values were –61.1, –58.9, –55.2, and –55.1 °C, respectively. During deacclimation, from the end of January to April 2012, cold hardiness of four cultivars gradually decreased. The LT₅₀ values in April, suggesting that cold-acclimated hardiness was lost, were –7.3, –7.7, –8.0, and –7.7 °C, respectively. According to LT₅₀ values, the difference in cold hardiness between ‘Daewol’ and ‘Kiraranokiwami’ was the most obvious throughout the whole period. The seasonal changes of cold hardiness representing with LT₅₀ values were closely related to those of total soluble sugars and sucrose in all the cultivars (P ≤ 0.001). Glucose content in ‘Fukuyokabijin’ (P ≤ 0.001) and fructose content in ‘Daewol’ (P ≤ 0.01) and ‘Aikawanakajima’ (P ≤ 0.001) were strongly related to cold hardiness. No correlation between cold hardiness and sorbitol content was shown in all the cultivars. Relative gene expression level of β-amylase, confirmed by a quantitative real-time RT-PCR, in four peach cultivars significantly increased during cold acclimation, showed a transient decrease in midwinter, and decreased during deacclimation. Expression of β-amylase was highly correlated with cold hardiness in all the cultivars (P ≤ 0.01).