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The cold hardiness of the buds in five cultivars of persimmon trees ( Diospyros kaki ) and four other Diospyros species during deacclimation in spring was examined by computer-assisted thermal analysis (TA) and by the freezing test under a constant freezing temperature (−10°C). TA revealed that the cold hardiness of the bud decreased, that is, exotherm temperature of the bud rose rapidly after budburst in all cultivars and species examined. The cold hardiness determined by the freezing test under a constant temperature was closely correlated with the developmental stage of the bud. It decreased rapidly as the bud swelled, and was the lowest around the time of budburst in all cultivars and species examined. After budburst, it gradually increased with shoot growth, somewhat differently with cultivars and species. In other words, all cultivars and species were the most susceptible to freezing injury at the budburst stage, but the cultivar- or species-specificity in cold hardiness was expressed by the hardiness of young shoots developed after budburst. Frost injury to persimmon trees caused by the untimely frost in mid-April at the experimental orchard of Kyoto University was discussed in terms of the time of budburst in each cultivar. |
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