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David M. Hunter and John T.A. Proctor

A system was developed to evaluate the response of grapes (Vitis spp. `Seyval') to soil-applied paclobutrazol. The youngest fully expanded leaf, and its axillary bud, on single shoots 6 to 9 nodes long developing on rooted softwood cuttings, were retained for use in a bioassay. The shoot that developed from the axillary bud exhibited a dosage-dependent growth inhibition following soil applications of paclobutrazol at 4 dosages between 1 and 1000 μg·g-1 soil. Other aerial components showed no response to paclobutrazol. This test plant system has potential for use in physiological studies with soil-applied plant growth regulators. Chemical name used: β -[(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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Charles J. Graham and J. Benton Storey

Pollarded `Wichita' pecan [Carya illinoensis (Wang) K. Koch] trees received 2 g uniconazol (UCZ) per tree using four application methods (trunk band, canopy soil injection, crown soil injection, and crown drench). All application methods increased trunk diameter but reduced shoot length, number of lateral shoots per terminal, nodes per terminal, internode length, and leaflets per compound leaf. Only the crown drench reduced leaf area. Area and dry weight per leaflet, and leaflet chlorophyll concentration were not affected by UCZ application. Effectiveness in growth reduction, as assessed by shoot elongation, was crown soil drench > crown soil injection > canopy soil injection > trunk band > control. All application methods increased viviparity. However, total yield per tree, nut size, and percentage of kernel were not affected. Chemical name used: (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazol).

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Duane W. Greene

Prohexadione-calcium (ProCa) has emerged as one of the most important management tools that an orchardist has available to control vegetative growth and to reduce the incidence and severity of fire blight. It has also been implicated in increased fruit set on treated apple trees. This investigation was initiated to confirm the effects of ProCa on fruit set and to evaluate different thinning strategies that might be used to appropriately thin treated trees. ProCa increased fruit set when applied at petal fall at initial rates of 125 or 250 mg·L−1 in three of the four experiments described in this article. Thinners were applied before, at the time of, and after application of ProCa. In all experiments, chemical thinners did not reduce fruit set to the same crop load level on ProCa-treated trees as they did on untreated trees. It was concluded that a different and more aggressive chemical thinning strategy must be used on trees that were treated with ProCa. Fruit size was reduced on ProCa-treated trees. This reduction was usually, but not always, related to increased fruit set. ProCa increased the number of pygmy fruit on ‘Delicious’ apple trees.

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David M. Hunter and John T.A. Proctor

Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced vegetative growth of `Seyval blanc' grapevines (Vitis spp.). At all rates, there was a reduction in internode length, while at rates higher than 10 μg a.i/g soil, there was also a reduction in node count. Leaf area produced following treatment declined in response to increasing rates, but specific leaf weight increased. Treatment with paclobutrazol delayed senescence and increased the retention of basal leaves that were nearly fully expanded at the time of treatment. Paclobutrazol application had no effect on fruit set or berry size, but the reduction in vegetative growth following treatment decreased the ability of the vine to supply sufficient photoassimilates for fruit maturation. Chemical name used: ß[(4-chlorophenyl)-methyl]-a-(1,1-dimethylethyl)1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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David M. Hunter and John T.A. Proctor

Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced photosynthetic CO2 uptake rate of leaves formed before paclobutrazol treatment within 3 to 5 days of treatment and the reductions were maintained for 15 days after treatment. The percentage of recently assimilated 14C exported from the source leaf was reduced only at the highest paclobutrazol dose, and there was little effect of treatment on the partitioning of exported 14C between the various sinks. In response to increasing doses of paclobutrazol, particularly at the higher doses, an increasing proportion of recent photoassimilates was maintained in a soluble form in all plant components. Reduced demand for photoassimilates as a result of the inhibition of vegetative growth may have contributed to a reduction in photosynthetic CO2 uptake rate, but this reduction in photosynthesis rate could not be attributed to a feedback inhibition caused by a buildup of starch in the leaves. Paclobutrazol had only a minor effect, if any, on photosynthetic electron transport. Chemical name used: β-[(4-chlorophenyl) methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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Toshiki Asao, Hiroaki Kitazawa, Takuya Ban, M. Habibur Rahman Pramanik, and Kenzi Tokumasa

Decomposition of benzoic acid in the nutrient solution with or without electrodegradation treatment. Benzoic acid is a potent growth inhibitor in the root exudates of strawberry plants ( Kitazawa et al., 2005 ). Four hundred micromolar benzoic acid solution

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Toshiki Asao, Hiroaki Kitazawa, Kazuyori Ushio, Yukio Sueda, Takuya Ban, and M. Habibur Rahman Pramanik

russell prairie gentian field) ( Table 6 ). It suggests that soil from a prairie gentian field has some growth inhibitors. In hydroponic culture, we also detected some growth inhibitors in the root exudates of the test plant ( Tables 4 and 5 ). Those

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Anita Solar, Jerneja Jakopič, Robert Veberič, and Franci Štampar

plant productivity or performance ( Rademacher, 1991 ). The results show that ProCa could be a useful growth inhibitor in walnut mother trees. Different patterns of vegetative growth reduction were observed after ProCa applications. The magnitude of a