Exothermic Characteristics of Dormant Buds of Persimmon (Diospyros kaki Thunb.) in Relation to Cold Hardiness

Abstract

Microcomputer-based thermal analysis (TA) was conducted on dormant mixed buds of Japanese persimmon (`Hiratanenashi'). The exotherms of buds were detected by thermoelectric modules. Flower buds of peach (Prunus persica Batsch cv. Shimizuhakuto) were also analyzed. When TA was used on a whole excised bud, including bud scales, the persimmon buds had only one exotherm at –14.3 °C, while the peach buds had high and low exotherms at –8.4 °C and –14.1 °C, respectively. However, when the exotherm was measured for the primordium, with the bud scales and transitional leaves removed, each primordium showed only one exotherm at –20.7 °C in persimmon and –11 °C in peach. Determination of killing temperature by visual observation, electrolyte leakage method, and triphenyltetrazolium chloride test revealed that the primordium of the persimmon bud was killed at about –14 °C as the excised whole bud or as the whole bud attached to the branch segment. Using the same method, the naked primordium was killed between –22 °C and –25 °C as the primordium was cooled. The peach primordium was killed at –14 °C when examined as a whole bud and at –11 °C as a naked primordium. Furthermore, the exotherm temperatures of persimmon buds and stem segments were measured at appropriate intervals during the two winter seasons 1993–95. Exotherm temperatures of persimmon buds were always higher than the low-temperature exotherm (LTE) temperatures of the stem segments and lower than the high-temperature exotherm (HTE) temperatures of the stem segments. LT50 of persimmon buds almost coincided with the exotherm temperatures of buds. A postulated role of bud scales in supercooling is discussed.