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Shulin Li and Preston K. Andrews

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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Michael D. Berg and Preston K. Andrews

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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Glenn R. Thayer and Preston K. Andrews

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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Preston K. Andrews and Margaret L. Collier

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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David W. Marshall and Preston K. Andrews

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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Preston K. Andrews and Margaret L. Collier

Effects of crop load and time of thinning on productivity of young `Fuji'/M.9 apple trees were tested by hand blossom (B) or fruit (F) thinning to two crop densities (fruit number/trunk cross-sectional area). Heavy (H) crop densities resulted in higher yields in both 2nd and 3rd leaf than light (L) crop densities. Time of thinning had no effect on yields in either year. In the 2nd leaf, fruit size was largest from trees B thinned to L crop densities, and smallest from trees F thinned to either crop density from mid-June through harvest. Both 1° and 2° vegetative growth were greatest in noncropped trees, intermediate in trees with L crops, and least in trees with H crops. Noncropped 2nd-1eaf trees had the highest flowering indices (flower clusters/100 total buds) the following spring and H cropped trees had the lowest. The flowering index was higher when trees were B thinned in the 2nd leaf than when F thinned. In the 3rd leaf, fruit size was largest when borne on weak upright shoots, intermediate on spurs, and smallest on 1-year-old terminal wood. Fruit on spurs had the highest incidence of sunscald (17%) and fruit on weak upright shoots the lowest (8%). Previous-season crop densities affected current-season's vegetative and fruit growth.

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Michael J. Willett, Preston K. Andrews and Edward L. Proebsting Jr.

There has been an explosion of interest in the development of computer-based Decision Support Systems (DSS) in agriculture. Humans factor, which is the design and evaluation of a system to optimize human and total system performance, offer tools to improve the usefulness of DSS. Task analysis, a formal human factors approach to study human-machine interaction, identifies all of the physical and psychological tasks which must be completed by either the human or the machine in order to meet the various system performance requirements and constraints. Our study focuses on the tasks associated with mid-winter stone fruit freeze protection. Using this technique we have identified work load and output requirements of current critical temperature estimation procedures, additional information needed to improve critical temperature estimates and training needs of fruit industry personnel making critical temperature determinations. This information will be used to produce a requirements specification for a freeze protection DSS.

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Michael J. Perry, Preston K. Andrews and Robert G. Evans

`Fuji' apples grown in the high light intensity of arid eastern Wash. are prone to sunscald damage. Evaporative cooling with over-tree sprinklers has become a commercially acceptable method for reducing the incidence of sunscald damage. A computer-controlled, over-tree evaporative cooling system was installed in a 3-yr-old commercial `Fuji'/M.9 orchard near Walla Walla, Wash. Over-tree sprinklers (Nelson R10 Mini Rotators) applied 280 or 560 1·min-1·ha-1 (30 or 60 GPM/A) when core temperatures were ≥33C (91.4F). Fruit skin and core temperatures were monitored with thermocouples. Fruit growth was not different between treatments. Skin color was improved by cooling, but the incidence of sunscald was low in all treatments. Commercial pack-out was measured and culls were evaluated. Fruit quality was analyzed at harvest and after 14 weeks storage. Titratable acids and soluble solids were higher in the 560 1·min-1·ha-1 treatment at harvest.

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Charlotte M. Guimond, Gregory A. Lang and Preston K. Andrews

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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Preston K. Andrews, Shulin Li and Margaret L. Collier

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.