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Cheryl R. Hampson, Harvey A. Quamme, Frank Kappel and Robert T. Brownlee

The effect of increasing planting density at constant rectangularity on the fruit yield, fruit size, and fruit color of apple [Malus ×sylvestris (L) var. domestica (Borkh.) Mansf.] in three training systems (slender spindle, tall spindle, and Geneva Y trellis) was assessed for 10 years. Five tree densities (from 1125 to 3226 trees/ha) and two cultivars (Royal Gala and Summerland McIntosh) were tested in a fully guarded split-split plot design. Density was the most influential factor. As tree density increased, per-tree yield decreased, but yield per unit area increased. The relation between cumulative yield per ha and tree density was linear at the outset of the trial, but soon became curvilinear, as incremental yield diminished with increasing tree density. The chief advantage of high density planting was a large increase in early fruit yield. In later years, reductions in cumulative yield efficiency, and in fruit color for `Summerland McIntosh', began to appear at the highest density. Training system had no influence on productivity for the first 5 years. During the second half of the trial, fruit yield per tree was greater for the Y trellis than for either spindle form at lower densities but not at higher densities. The slender and tall spindles were similar in nearly all aspects of performance, including yield. `Summerland McIntosh' yielded almost 40% less than `Royal Gala' and seemed more sensitive to the adverse effects of high tree density on fruit color.

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Pedro B. Oliveira, Cristina M. Oliveira and António A. Monteiro

The aim of this study was to determine the effects of date of summer pruning and cane densities on growth and fruiting characteristics of the raspberry (Rubus idaeus) plant. Three summer-pruning dates (early, middle, and late July) and four cane densities (8, 16, 24, and 32 canes/m row) were imposed to the greenhouse-grown primocane-fruiting raspberry `Autumn Bliss' in 2 consecutive years (1994 and 1995). A higher light microclimate and CO2 assimilation rate were measured within the canopy at the lowest density. Some compensation in CO2 assimilation rates were observed in the upper leaves of the high-density treatments, probably in response to low light. Delayed pruning decreased yield per cane and per row. The highest yields per cane were always observed at the lowest cane density. Densities of 16 and 24 canes/m produced the highest fruit yield. Light conditions appeared to be the most important environmental factor affecting plant productivity. Fruit were a weaker sink than roots; therefore, the role of carbohydrate reserves should be investigated.

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Francisco Radillo Juarez, Juan Manuel González Gonzalez, Marcelino Bazan Tene and J. Hyvan Castañeda Alvarez

Vegetables are important in Mexican agriculture because of the exportation opportunities made available by the opening of the Free Trade Agreement. Okra represents a potentially profitable crop, and it is important to understand its behavior in a predetermined environment, and determine its optimal sowing density. The present work was realized to evaluate three genotypes and three densities of okra plants in the production and quality of fresh fruit. The work was realized in the winter–spring cycle in the dry tropic region, using a randomized block design with a bifactorial of nine treatments. During the cultivation cycle, the vegetative and productive variables did not present changes in phenology, and only registered differences in plant height (58.4 and 57.6 cm., respectively) of PX 416543 and `Green Best', with a distance between plants of 18 cm. These results indicate that with increased densities of 41,600, 50,000, and 69,444 plants/ha, there were no differences in the number and weight of fresh fruit/plant. Nevertheless, with the production and support the quality of fresh fruit increased. We conclude that high densities of plants increase the total crop of fresh fruit per hectare without affecting quality. The variety PX 416543 presented the best vegetative and productive behavior.

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Lauren C. Garner and Thomas Björkman

Mechanical stimulation is known to control excessive stem elongation in high-density tomato (Lycopersicon esculentum Mill.) transplants. Mechanical stimulation using physical impedance provided height control equivalent to that obtained using brushing. Low-cost materials can be used to apply the impedance. Mylar film in a plastic frame was equivalent to expensive acrylic sheets in its effect on plant height (40 mm shorter than nontreated, a 40% reduction in the elongation rate during the treatment period), stem diameter (18% thicker), and biomass (14% lighter) when they applied a pressure of 66 N·m-2. Stem elongation was not reduced if less pressure was applied (25 or 50 N·m-2). Height control was equally effective with a solid material (mylar film) and a permeable material (fiberglass insect screen), indicating that restricting air movement is not an important mechanism for the growth response. Overnight treatments resulted in the desired growth response (27 mm shorter than nontreated, a 30% reduction in elongation rate), but 0.5-h treatments had insufficient effect for commercial use (11 mm shorter, 10% reduction in elongation rate). These experiments demonstrate that impedance can be used in commercial production conditions to control tomato transplant height with inexpensive materials. However, satisfactory height control requires a large applied force and a long daily treatment period.

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D.J. Tennessen and P.S. Berlind

Shade-avoidance in plants can result in tall, spindly, and unmarketable plants. Because plant spacing and shade can signal shade avoidance, we grew chrysanthemum (Chrysanthemum grandiflora Ramat, cv. Nob Hill) under two planting densities to characterize the normal plant response to crowding. Plants grew 72 ± 4 cm and developed 17 ± 3 floral branches under 55-cm spacing, while plants grown in close proximity (15-cm centers) grew 78 ± 3 cm and developed 7 ± 1 floral branches under a 12-hour photoperiod. Because phytochrome-A overexpression is known to create dwarf plants, we were interested in transforming `Nob Hill' to alter its phenotype. Sterile leaf and stem cuttings of `Nob Hill' were transformed to express phytochrome-A (Phy-A) from oat (provided by R. Vierstra) using Agrobacterium tumefaciens. The method of Ledger et al. [Plant Cell Reports 10:195 (1991)] was improved when we used internodal segments as described by Yepes et al. [Plant Cell Reports 14:694 (1995)] for a 58% regeneration efficiency. Transformants were screened by selective media and confirmed by southern blots using monoclonal antibodies provided by R. Vierstra. Transgenic and control plants were grown in a greenhouse at 20°C day and 18°C night temperatures with a 14-hour photoperiod. At 4 weeks old, transgenic plants (11 ± 2 cm) were shorter than control plants (15 ± 3 cm). The use of this new transgenic chrysanthemum for high-density mum production is discussed.

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Curt R. Rom

Current practices of fertilizer management, potential problems, and paths for fertilizer management research were discussed. Apple nutrition management in the humid southern regions of the U.S. is typically challenged by several factors such as inherently low soil pH, variable soil chemistry, and irregular precipitation. Some literature and personal experiences with orchard replant conditions and fumigation, fertigation, fertilizer delivery system, and time of fertilizer application were reviewed. On replant sites, fumigation and liming significantly improved tree survival and growth in the first 5 years. Fertigation with ammonium nitrate significantly lowered soil pH in the root zone compared to top dress applications. Using calcium nitrate resulted in less pH reduction. Results of studies of autumn application of N fertilizers have been mixed, with reports of no, decreased, or increased effects on fruit set, yield, and growth. Studies with size-controlling rootstocks indicate additional need to study the uptake of Mn and related Mn toxicity. Precocious rootstocks with high early yields have resulted in foliar K levels approaching deficiency within the first 10 years of production. Indications are that high-density orchards may have additional requirements for K fertilizers.

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Justin R. Morris

The moderate consumption of red wine, grapes, raisins, and grape juice has a demonstrably positive effect on human health. Scientifically conducted surveys have shown that the effects of moderate intake of red wine reduces circulatory disease. Legislative efforts on labeling red wine to show the scientific evidence of this statement are receiving favorable attention. The antioxidant resveratrol, present in the skins of the grape in any of its various forms, is believed to be the agent primarily responsible for the healthful benefits demonstrated. It has been shown to affect lipid metabolism in higher mammals. Studies of resveratrol content in a variety of wine grapes are being performed at the Univ. of Arkansas, as well as at other institutions. Red wine (in contrast to white wine and other alcoholic beverages) reduces clotting ability and increases levels of high-density lipoproteins (“good” cholesterol), which diminishes the risk of coronary problems. Grape skin extract, red wines, and red juice appear to enhance the ability of blood vessels to resist vasoconstriction and to contribute to antithrombotic activity. In laboratory tests, several known antioxidants in wine out-performed vitamin E, the current best-known dietary antioxidant.

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

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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James R. Dunlap, Sarah E. Lingle and Gene E. Lester

Postharvest ethylene production and ACC levels were determined in netted muskmelon fruits (Cucumis melo L. var. reticulatus `Magnum 45') exposed to temperature extremes by heating for 3 hr at 45C and/or storage at 4C. The possibility of using seal-packaging to protect the fruit against temperature-induced changes in ethylene production was examined by wrapping melons before treatment with a high-density polyethylene (HDPE) shrink-film. Ethylene production measured in fruit immediately after heating or removal from refrigeration was only 30% of the level determined before treatment, and continued to decline during refrigerated storage. However, the concentration of ACC in these same tissues remained constant or even increased slightly during storage. Wrapping fruit in HDPE film had no effect on the tissue concentrations of ACC or capacity for ethylene synthesis. In contrast to initial measurements, heated or refrigerated fruit held at room temperature (25C) for 24 hr produced ethylene at rates that equalled or exceeded the levels for freshly harvested fruit. These results strongly suggest that temperature-imposed restrictions on ethylene synthesis by netted muskmelon fruit are reversible and occur at the step responsible for converting ACC to ethylene via EFE rather than in the synthesis of ACC. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC).

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Don C. Elfving, Gregory A. Lang and Dwayne B. Visser

Prohexadione-Ca (P-Ca) and ethephon (ETH) were evaluated as potential inhibitors of growth and promoters of early flowering for high density orchard management of sweet cherry (Prunus avium L.) trees on vigorous rootstocks. Single applications (P-Ca at 125 to 250 mg·L-1 active ingredient (a.i.) or ETH at 175 to 200 mg·L-1 a.i.) to young, nonfruiting sweet cherry trees produced short-term, generally transient reductions in terminal shoot elongation, and did not stimulate flower bud formation. Tank-mix applications (P-Ca + ETH) usually produced a stronger, possibly synergistic, reduction in shoot growth rate. Single tank-mix applications either increased subsequent flower bud density on previous season shoots or had no effect; when a second application was made three weeks later to the same trees, subsequent flower bud density on previous season shoots and spurs on older wood increased ≈3-fold over untreated trees. Yield efficiency (g·cm2 trunk cross-sectional area) also increased nearly 3-fold. Chemical names used: (2-chloroethyl) phosphonic acid (ethephon); calcium 3-oxido-4-propionyl-5-oxo-3-cyclohexene carboxylate (prohexadione-Ca); polyoxyethylene polypropoxypropanol, dihydroxypropane, 2-butoxyethanol (Regulaid); aliphatic polycarboxylate, calcium (Tri-Fol).