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  • Author or Editor: H. O. Jackson x
  • HortScience x
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Abstract

A method of exotherm analysis is described for determining the cold hardiness of dormant peach flower buds (Prunus persica (L.) Batsch). Twig pieces with intact flower buds were placed into thermos bottles and cooled at a constant rate in a programmed cold chamber. A thermocouple was inserted in the node of each twig piece to measure the temperature at which sudden heat release occurred. Thermocouples connected in series made it possible to record exotherms of 5 twig pieces from a cultivar on a single channel of a multipoint recorder. The exotherm method was compared to the LT50 method (the temperature at which 50% of the flower buds are killed) using 10 cultivars on one collection date. The mean temperatures at which the exotherms were initiated were significantly correlated with the LT50 (r = +.880). In addition, the mean temperatures at which exotherms were initiated and the LT50 for these cultivars were significantly correlated with the percentage of flower bud mortality averaged over 4 winters (r = −.667 and −.797, respectively). The exotherm method gives a direct measurement of the temperature at which peach flower buds are killed and offers an opportunity for studying the cold hardiness of individual flower buds not possible with other methods.

Open Access

Abstract

An inexpensive chamber for controlled freezing of large container-grown plants up to 2 m in height was constructed using liquid nitrogen as a refrigerant. A microcomputer-based system was developed to control the cooling sequence and to collect data on tissue temperature, air temperature, and exotherms. Versatile software was written that allowed the programmed rate of temperature drop to be based on either tissue temperature or air temperature.

Open Access