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- Author or Editor: H. O. Jackson x
Bearing trees of ‘Loring’, ‘Redhaven’ and ‘Babygold 5’ peach trees (Prunus persica (L.) Batsch) on Siberian C seedlings defoliated earlier than those on the other seedling rootstocks. Early cold acclimation of scions in the fall and scion cold hardiness in mid-winter were enhanced more by Siberian C seedlings than by those of the other seedling rootstocks. Bud survival and fruit set of ‘Redhaven’ and ‘Bablygold 5’ scions were greater on Siberian C seedlings than on any of the other seedling rootstocks following an outdoor cold stress at -23.4°C in January. The cold hardiness of phloem, cambium, and xylem stem tissues were closely correlated with each other in the fall, but were not correlated with cold hardiness of flower buds on the same shoots. Seedlings of Siberian C appeared to enhance early scion dormancy and they increased scion bud hardiness by as much as 4.7° in the fall, and 1.3° in mid-February, compared with those of other rootstocks tested.
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.
An 8-year study was made to assess the performance of Harrow Blood and Siberian C rootstock seedlings in comparison with the commercial seedling rootstocks Rutgers Red Leaf, Veteran, Halford and Bailey. Rootstocks significantly influenced tree size of ‘Loring’, ‘Redhaven’ and ‘Babygold 5’ peach (Prunus persica (L.) Batsch). Siberian C had the largest influence on size control, reducing tree volume by about 20%. Tree height and spread, trunk circumference and trunk cross-sectional areas were also influenced by rootstocks, but annual growth of terminal shoots was not. Rootstocks influenced crotch angle development of ‘Loring’, but had no effect on crotch angle development of ‘Redhaven’ or ‘Babygold 5’. Cropping efficiency of ‘Babygold 5’ was influenced by rootstocks but cropping efficiency of ‘Redhaven’ and ‘Loring’ were not. Yields were significantly influenced by rootstocks. The highest cumulative yields of ‘Loring’ were on Veteran seedlings, the highest of ‘Redhaven’ were on Rutgers Red Leaf and the highest of ‘Babygold 5’ were on Halford. Yields were also a function of tree size with the highest yields being obtained on the largest trees. Trunk circumference and crosssectional area were the only growth measurements that were significantly correlated with the yield of each cultivar. Tree survival was best on Harrow Blood and Siberian C and poorest on Rutgers Red Leaf and Veteran. Tree mortality was associated with winter injury and canker (Leucostoma spp.) infection but not with incompatibility.
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.