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  • Author or Editor: Preston K. Andrews x
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An aeroponic growth chamber is a system for growing plants in air with water and nutrients supplied by intermittent mist. This type of plant growth system is especially useful for experiments where root accessibility is desired. Tomatoes (Lycopersicon esculentum L. `Bonnie Best') were used to test the performance of an aeroponic growth chamber. A nutrient solution mist was applied through spray nozzles suspended below roots of supported seedlings. Mist application was regulated by electric timers, so that mist was applied for 50 sec. every 5 min. during the 16-hr light period, which was supplemented with a high-pressure sodium lamp. Root and stem lengths, leaf number and leaf lengths were measured weekly. Plastochron index (PI) was used to measure rate of leaf initiation. PI increased linearly, indicating uniform initiation of leaf primordia and absence of environmental stresses. Stem and root lengths increased consistently throughout the growing period. Each plant was harvested, separated into leaves, shoots and roots, oven dried, and dry weights measured.

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Dwarfing rootstocks are essential for developing high-density pear orchards with increased precocity. The graft compatibility of Amelanchier alnifolia, A. x grandiflora, A. canadensis, and A. alnifolia `Thiessen' as a rootstock for `Anjou' pear or as an interstock on `Bartlett' seedling, `Old Home × Farmingdale' and Crataegus rootstocks are being tested. Twenty rootstock and rootstock/interstock combinations were top grafted 27 Jan. 1994. Ten replicates will be planted in pots for each graft combination in March after callusing. Growth of successful graft combinations will be measured every two weeks. Shoot length and diameter and trunk diameter at a designated reference point will be measured. Leaf color will be evaluated periodically using a Minolta colorimeter. At natural leaffall, leaf areas will be measured. Graft compatibility will be evaluated. All data will be analyzed by analysis of variance.

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The activities of the fruit ripening enzymes cellulase, polygalacturonase (PG) and pectin methylesterase (PME) were detected during the development of sweet cherry (Prunus avium L.) fruit. Cellulase and PG activities of pericarp tissue increased 4-10 times between hypanthium abscission and harvest. PME activity remained high throughout this period of fruit development. There was a positive correlation between the anthocyanin content of the pericarp and both cellulase and PG activities. Concomitant with the increases in the activities of these ripening enzymes was a decrease in fruit firmness. The increases in cellulase and PG activities were checked following two-weeks storage at 10 C after harvest. The purification and characterization of the putative cellulase and PG enzymes will be discussed, together with attempts to chemically inhibit their activities and modify fruit softening.

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Washington is the leading producer of apples in the United States. North-central and south-central Washington and the Columbia Basin are the major production regions within the state. The climate of these production regions is characterized by cold winters and hot, dry summers with high levels of light intensity. The principal varieties produced are still `Delicious', `Golden Delicious', and `Granny Smith'; however, `Fuji', `Gala', and `Braeburn' have been planted widely since 1988. Despite increasing levels of production and lower prices beginning in 1986, apple prices have recovered relatively well in recent years due to aggressive exports to southeast Asia and Mexico. Increased international competition has resulted in a trend towards higher-density orchards using dwarfing rootstock so that earlier production can be achieved. Evaluation of the performance of new varieties in Washington's climatic conditions has increased. Although not the focus of this article, several social and environmental issues are facing the Washington apple industry, including increasing restrictions on chemical usage, competition for a limited water resource, regulation of ground water quality, pending labor relations legislation, and increasing urbanization pressures.

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Variability in maturity and quality of sweet cherry (Prunus avium L. `Bing') fruit at harvest is a major limitation to the crop's storage and marketing potential. Later blooming flowers resulted in poorer fruit quality Differences in bloom date were related to differences in flower primordial development during winter. Vigorous shoots grown in the previous season produced fewer flower buds per length of shoot than did shorter, less vigorous shoots, resulting in larger flower primordia on vigorous shoots, The effects on primordial and fruit development of altered leaf areas per flower bud the previous summer were examined. A decrease in leaf area per bud during summer reduced primordium size in mid-winter. Dormant flower primordia of 6-yr-old `Bing' trees on precocious `Giessen' rootstock, Gil48/1, were larger than those with `Mazzard' as rootstock. Flower primordia on dwarfing Gil48/8 rootstock were intermediate in size. Differences in primordial development and bloom date, whether due to management practices or rootstock, may affect fruit development and contribute to variability in fruit maturity and quality.

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Abstract

The development of deep supercooling in sweet cherry (Prunus avium L. ‘Bing’) and peach [Prunus persica (L.) Batsch ‘Redhaven’] flower buds during late summer and early autumn was measured by differential thermal analysis. The capacity to deep supercool developed under ambient conditions during September in both 1982 and 1983. It developed 1-2 weeks earlier in sweet cherry than in peach flower buds. Exposing a sweet cherry limb in situ to daily 15° day/5°C night temperatures beginning in early Aug. 1983 advanced the development of the flower buds’ capacity to deep supercool by 4 weeks. Sweet cherry flower buds whose capacity to deep supercool was advanced by exposure to these cool temperatures displayed a median low-temperature exotherm (LTE50) near - 20°. This demonstrated the potential capacity of sweet cherry flower buds to avoid injury during moderate freezes as early as mid-August.

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Abstract

Seasonal changes in the temperature of the median low-temperature exotherm (LTE50) of dormant sweet cherry (Prunus avium L. cv. Bing) flower buds were significantly correlated with the preceding minimum air temperature in the orchard and the water content of the flower primordia. When buds were exposed to temperatures just below the high temperature exotherms, water migrated from the primordia to the bud scales. Under these conditions, the LTE50 decreased almost 5°C during the first day, but only 1°/day thereafter. The minimum LTE50 was near −32° after the buds were frozen for 10 days. Thawing buds at 0° or above increased the LTE50 about 1°/hr, to −20° to −21°. The LTE50 did not increase above these temperatures until the buds were exposed to 20° for 1-2 days following the completion of rest. During deacclimation, both the LTE50 and temperature range of the low temperature exotherms (LTEs) increased. These changes were accompanied by fluctuations in the capacity of the flower buds to exhibit deep supercooling, expressed as the fraction of an LTE produced per flower primordium (LTE/primordium). Even on days when the LTE/primordium was low, the temperature required to injure 50% of the flower primordia was similar to the LTE50.

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To examine the effect of timing and severity of summer pruning on flower bud initiation and vegetative growth, 4-year-old `Bing' cherry trees (Prunus avium L.) were pruned at 31, 34, 37, 38, or 45 days after full bloom (DAFB) with heading cuts 20 cm from the base of current-season lateral shoot growth, or at 38 DAFB by heading current-season lateral shoot growth at 15, 20, 25, or 30 cm from the base of the shoot. The influence of heading cut position between nodes also was examined by cutting at a point (≈20 cm from the shoot base) just above or below a node, or in the middle of an internode. Summer pruning influenced the number of both flower buds and lateral shoots subsequently formed on the shoots. All of the timings and pruning lengths significantly increased the number of both flower buds and lateral shoots, but differences between pruning times were not significant. There was significantly less regrowth when shoots were pruned just below a node or in the center of an internode, rather than just above a node, suggesting that the length of the remaining stub may inhibit regrowth somewhat. The coefficient of determination (r 2) between flower bud number and regrowth ranged from -0.34 to -0.45. In young high-density sweet cherry plantings, summer pruning may be useful for increasing flower bud formation on current-season shoots. The time of pruning, length of the shoots after pruning, and location of the pruning cut can influence subsequent flower bud formation and vegetative regrowth.

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Young sweet cherry (Prunus avium) trees are typically upright, vegetatively vigorous, and nonprecocious, taking 5 to 6 years to come into production. To produce fruit in high-density orchards by year 3 or 4, development of lateral shoots for potential fruiting is critical in year 2 or 3. An experiment was designed to promote lateral branching on 2-year-old trees. The experiment was conducted in a commercial orchard in Roosevelt, Wash., with `Bing' and `Van' on the vigorous rootstocks Mazzard and Colt. The trees were planted at 415 trees per acre with three scaffolds trained into a “V” canopy design. The experimental variables were treatments with and without Promalin (1.8% BAP plus 1.8% GA4+7), applied at a ratio of 1:3 in latex paint at green tip stage; superimposed on these treatments were either heading cuts of each scaffold to 2 m long (or tipping the scaffold if it was <2 m), removing four to five buds subtending the terminal bud, a combination of heading and bud removal, or controls. On trees that were not treated with Promalin, three additional treatments included either removing subtending buds at budbreak, or removing buds at multiple locations along the scaffold at green tip or at budbreak. New lateral shoots were counted 4 weeks after budbreak, and the quality of the shoots (shoot diameter and angle of emergence) was measured at the time of summer pruning. Interactions between Promalin, bud manipulation, and pruning will be discussed in relation to development of canopy structure.

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The development of sweet cherry (Prunus avium L., `Bing') flower buds from winter through anthesis was examined. Shoots were collected from the top and bottom of the canopy. The weight and size of flower buds and primordia produced on last-season's and 1-year-old wood were measured. As early as mid-December bud and primordia size and weight were greater on last-season's wood than on 1-year-old wood, with the largest and heaviest buds and primordia produced on last-season's wood in the bottom of the canopy. There was a significant negative correlation between the number of primordia per bud and primordium weight. The relationship between flower bud and primordia size during mid-December and ovary size at anthesis suggests a causal relationship, which may be a major source of variation influencing harvested fruit size and quality.

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