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Bruce W. Wood

cropload trees (i.e., “off” year of AB cycle). This raises the possibility that timely application of phytohormones or bioregulators to tree canopies might alter the phytohormonal environment of primordia in such a way as to enable control of pistillate

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George Ouma and Frank Matta

Experiments were performed in 1995 and 1996 at the Mississippi State Univ. Agricultural Experiment Station, Pototoc Ridge, to investigate the effect of Accel and carbaryl sprayed 2 weeks postbloom on fruit set, yield, and plant nutrition of three apple cultivars (Empire, Jon-A-Red, and Braeburn). The treatments consisted of Accel 25 ppm, Accel 50 ppm, Accel 75 ppm, Carbaryl 0.05%, Carbaryl 0.1%, Carbaryl 0.2%, and an unsprayed control. Thinning trials using the two bioregulators conducted over 2 years indicated that Accel and Carbaryl consistently thinned the apple cultivars and increased the yields. Leaf mineral concentrations were affect by the treatments. In 1995, the treatments affected leaf concentrations of N, Ca, and Mg, while in 1996 the treatments affected the leaf contents of N, P, K, Ca, Mg, Fe, Mn, and Zn, but no copper. The treatments also affected the fruit flesh mineral concentration by increasing the contents of K, P, and Mg in 1996. It can therefore be concluded that, depending on apple cultivar, N content was reduced by the treatments while Ca and Mg were generally increased. Similarly, the fruit flesh contents of Fe, K, P, and Mg were also increased. The two bioregulators therefore thin apples, increase yields, and affect the fruit quality.

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S.R. Drake, T.A. Eisele, M.A. Drake, D.C. Elfving, S.L. Drake, and D.B. Visser

This study was conducted over three crop seasons using 'Delicious' (Scarletspur strain) apple trees on MM.111 rootstock. The bioregulators aminoethoxyvinylglycine (AVG) and ethephon (ETH) were applied alone or in combinations at various time intervals before harvest. Fruit response to bioregulators was evaluated at harvest and after storage. AVG applied 4 weeks before first harvest retarded starch loss at harvest, retained greater firmness, and reduced internal ethylene concentration and watercore of fruit at harvest and after both regular and controlled atmosphere storage. AVG did not influence peel color (hue values), but the flesh color of treated apples was more green. AVG in all instances tended to reduce the sensory scores for apples and apple juice. In contrast, ETH enhanced starch hydrolysis, flesh color development (green to more yellow), and soluble solids concentration while reducing titratable acidity levels. ETH had no influence on fruit firmness at harvest, but reduced firmness levels after storage in an inverse relationship to the concentration applied. Sensory values for whole apples were not influenced by ETH treatment, but ETH improved sensory preference for apple juice, particularly at early harvest. Applying AVG before ETH enhanced soluble solids and sensory scores for both fruit and juice. Treating with AVG followed by ETH at 150 mg·L–1 permitted the maintenance of satisfactory firmness values (>53.4 N) after long-term storage along with better quality and sensory perceptions. Using specific combinations of both AVG and ETH permitted ETH-mediated improvements in objective and perceived fruit quality to be obtained without the losses in flesh firmness and storability due to uncontrolled ethylene evolution and ripening typically observed when ETH is applied alone preharvest.

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D.C. Elfving

Some cultivars of deciduous tree fruit, especially in apple and pear, tend to come into bearing slowly. Bioregulators have been used to stimulate flowering and cropping in slow-to-crop cultivars, but success has been variable. Improved flowering may not necessarily lead to increased cropping. Reduction in vegetative vigor as a result of bioregulator treatment is often, but not always, associated with increased flowering. Bioregulators that act by interfering with gibberellin biosynthesis or that generate ethylene in plant tissues have proven effective for increasing flowering under a variety of conditions. Few studies have demonstrated that exogenous bioregulator applications to poorly cropping fruit trees can be used to produce sustained and economically significant improvement in fruiting while maintaining satisfactory fruit quality.

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William C. Mitchell and Gregory A. Lang

Fall application of 2-chloroethylphosphoric acid (ethephon) is known to delay spring budbreak in peach (Prunus persica). To study seasonal variation in peach response to dormancy-breaking plant bioregulators and their possible interaction with ethylene, peach shoots were cut in the field at various intervals during endodormancy. Shoots were dipped in the dormancy-breaking bioregulators hydrogen cyanamide (H2CN2, 100 mM) or gibberellic acid (KGA3, 130 μm), alone or in combination with 1.38 mM ethephon. Treated shoots were held in beakers of either tap water or 1 mM silver thiosulfate (STS), and placed in growth chambers with potassium permanganate traps, 12/12 h photoperiods and 21/26 C temperature regimes. Dormancy-breaking efficacy (apical budbreak at 21 days) of both bioregulators increased as endodormancy progressed. At all intervals, H2CN2, broke dormancy more effectively than KGA3. The addition of ethephon to H2CN2 application prior to any CU accumulation (20 Oct) had no effect on efficacy (80% budbreak), but its addition after accumulation of ∼50 CU (8 Nov) or ∼320 CU (14 Dec) reduced subsequent budbreak to 25% and 40%, respectively. The addition of ethephon to KGA3 applications reduced budbreak both prior to (27 Oct) and after (8 Nov) initial CU accumulation. STS in the beaker solution increased both the extent (27 Oct) and the rate (14 Dec) of KGA-induced budbreak The interaction of ethylene, bioregulator type, and endodormancy regulation will be discussed.

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A. Belakbir, J.M. Ruiz, and L. Romero

To test the effectiveness of different bioregulators in enhancing bell pepper (Capsicum annuum L.) yield and fruit quality, the commercial bioregulators CCC, NAA, GA3, and Biozyme® were sprayed on plants at flower initiation, followed by two additional applications at 30-day intervals. Biozyme produced a significant increase in total yield but ≈40% of the fruit were not marketable. Treatment with NAA produced the highest yield of marketable fruit. Treatments did not affect fruit firmness compared to the control. Gibberellic acid increased fruit ascorbic acid and citric acid concentrations and Biozyme, GA3, and CCC increased fruit soluble solids content. Biozyme treatment increased fruit fructose, sucrose, carotenoid, and lycopene concentration. Treatments had no effect on fruit calcium concentration or pH. Chemical names used: chlormequat chloride (CCC); naphthaleneacetic acid (NAA), gibberellic acid (GA3); GA3 + IAA (indoIe-3-acetic acid) + zeatine + micronutrients (Biozyme®).

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Kathleen M. Williams and Esmaeil Fallahi

The use of exogenous plant bioregulators or plant hormones to adjust crop load in apple (Malus ×domestica Borkh.) and promote regular cropping remains challenging to both researchers and producers. Responses to these hormones are sensitive to the rate and timing of application, to physiological status of the tree, orchard system, variety, rootstock, and a myriad of cultural practices and environmental factors. Of the environmental factors, temperature plays the most important role in determining response and efficacy of a given material. All classes of plant bioregulators have been used over the past 30 to 40 years as postbloom chemical thinning materials. Most of the standard postbloom thinning programs involve application of a synthetic auxin, such as naphthalene acetic acid (NAA) in combination with carbaryl (Sevin), a commonly used insecticide. The mode of action of these two compounds is not clearly understood. Gibberellins generally have not been effective thinning materials for apple because of their negative impact on return bloom. Ethylene-releasing compounds have been used successfully as postbloom thinning materials. Cytokinins, particularly synthetic sources such as 6-benzyladenine (6-BA), have been shown to effectively thin fruit and enhance fruit size on many commercial varieties. The rate and timing of 6-BA applications are critical to obtain desirable thinning and fruit size responses. The use of these different bioregulators is essential for regular cropping of apple, particularly for spur `Delicious', `Fuji' and other varieties that are difficult to thin chemically and which are prone to severe alternate bearing. The focus of this discussion is the use of these bioregulators in commercial apple production areas in the United States.

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Ki-Yun Jung*, Bong-Hwa Kang, Yu-Jin Park, and Jung-Myung Lee

Double-stemmed seedlings (DSS) will be favored by the growers because they can save the expense needed to purchase commercial seedlings. This is also true with grafted tomatoes since the price of grafted tomato seedlings is about 2 times higher than non-grafted ones. The plug seedling growers will also benefit from the increased demand for DSS if the production cost for DSS can be maintained at appropriate level. Two stem cuttings having two expanded leaves were taken from a seedling when the seedling had four expanded leaves and rooted in 32-cell trays filled with commercial soil mix. Lower stem cuttings having first and second leaves produced well-balanced DSS even without any plant bioregulator treatment whereas up upper stem cuttings having third and fourth leaves resulted in single-stem seedlings with very limited outgrowth of axillary shoot from the third node. DSS can be obtained from the decapitated seedling stump by outgrowth of axillary shoots from the cotyledonary nodes, but the quality and uniformity were inferior to other seedlings. Pinching off the tips of seedlings thus leaving three expanded leaves per seedling and application of plant bioregulators to the decapitated seedlings were also effective for producing DDS. Application of thidiazuron (TDZ) in lanolin paste to the second node was most effective even though whole plant spray with TDZ or BA was also partially effective. Subsequent growth characteristics of these seedlings will be further discussed.

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Marisa Y. Thompson, Jennifer Randall, Richard J. Heerema, and Dawn VanLeeuwen

.W. 2011b Influence of plant bioregulators on pecan flowering and implications for regulation of pistillate flower initiation HortScience 46 870 877 Wood, B.W. Lombardini, L. Heerema, R.J. 2009 Influence of aminoethoxyvinylglycine on pecan fruit retention

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Marisa Y. Thompson, Jennifer J. Randall, Dawn VanLeeuwen, and Richard J. Heerema

586 589 doi: 10.21273/HORTSCI.46.4.586 Wood, B.W. 2011b Influence of plant bioregulators on pecan flowering and implications for regulation of pistillate flower initiation HortScience 46 870 877 doi: 10.21273/HORTSCI.46.6.870 Wood