Study on the evaluation method of cold hardiness in deciduous fruit trees and its application.

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This study was aimed firstly to establish a reliable and rapid method of evaluating cold hardiness of some deciduous fruit species, for which we examined thermal analysis using thermoelectric modules as the detectors which enabled us to measure many bud samples at the same time. Secondly, after demonstrating the validity of the method, we characterized the supercooling characteristics of persimmon and its related species during acclimation and deacclimation processes in the dormant season and discuaaed the cold hardiness of this fruit species.1)When thermal analysis was conducted with dormant buds of persimmon attached to branch segments, two exotherms detected did not coincide with the lethal temperature of the buds. When the detached buds were analyzed, only one exotherm was detected and coincided with their lethal temperature. This result suggested that thermal analysis should be done with detached buds to evaluate their cold hardiness. Furthermore, lethal temperature of branch segm … More ents was substantially lower than that of dormant buds, which also suggested that cold hardiness should be evaluated on dormant buds.2)When dissected bud primordia of persimmon with their bud scales removed were thermal-analyzed, their exotherm temperature became lower than the lethal temperature of intact bud, indicating that bud scales of persimmon did not have any protective role to the cold hardiness of whole bud and even reduced its supercooling ability.3)Comparisons of thermal analysis between fruit species revealed that dormant buds of apples, pears and peaches survive freezing temperature by extraorgan freezing, while those of grapes and persimmons do so by real supercooling. These different freezing resistance mechanism among fruit species appeared to be related to the anatomical features of bud.4)The effect of air temperature in the winter on the cold hardiness of persimmon was examined in relation to bud dormancy. Before dormancy release, the ambient air temperature, either high or low, had on effect on the bud cold hardiness, while once the dormancy was released, untimely warm temperature decreased cold hardiness considerably.5)All the persimmon cultivars and other four Diospyros species examined were the most susceptible to frost damage at around the time of budburst, but the cultivar-or species-specificity in cold hardiness was expressed by the hardiness of young shoots developed after budburst. Less