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Corina Serban and Lee Kalcsits

trees with relatively low crop loads and strong shoot growth, fruit Ca concentrations were not consistently improved by using shoot growth-inhibiting plant growth regulators. Fruit yields and weight were not predictably affected by manipulating shoot

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Osamu Kawabata and Joseph DeFrank

A modified power function, y = (A + B·x)–C, was developed for determining the relationship between plant growth and growth retardant treatment. This function accounts for the plant response characteristics by incorporating three coefficients: A, growth level of the nontreated plants; B, the degree of growth reduction; and C, the smallest effective dose of the growth inhibitor. The function accounted for 97% of the variation in purple nutsedge (Cyperus rotundus L.) leaf length as a function of the amount of a growth retardant applied. The procedure resulted in a smaller error sum of squares than several common nonlinear functions because of its greater shape flexibility.

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Hsin-Shan Lin and Chien Yi Wang

Off-season production of several tropical and subtropical fruits has been successfully practiced commercially in Taiwan. By combining pruning, removal of leaves, and application of growth regulators, it is possible to have two to three crops of grapes per year. By grafting the chilled scions of temperate Asian pear onto the water shoots of low-chilling native pear varieties, it is possible to produce high-quality Asian pears (temperate-origin) in a subtropical environment. By using techniques such as root-pruning, flooding, and application of growth inhibitors, it is possible to induce flower bud formation and hasten the production of wax apples. The production periods of other fruit crops such as jujubes and sugar apples, can also be modified by pruning and other techniques.

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Arvazena E. Clardy, Sabrina L. Shaw, and William F. Hayslett

Red Delano chrysanthemum cuttings were transplanted into 15 cm pots. Fertilizer treatments were started immediately. Initial fertilizer rates were 14.8 cc of the designated formulation per pot. Two formulations of fertilizer, 20-20-20 and 5-50-17 NPK, were used in excessive rates to determine if it would override the effects of the growth inhibitors. Paclobutrazol, uniconizole, and daminozide were used to retard growth. Three rates-30, 60, and 120 ppm of paclobutrazol, and 10, 20, and 40 ppm of uniconizole and one rate of 25 % daminozide were foliar applied (two applications) on the plants. After two weeks the plants were treated with the growth retardants and an additional treatment of fertilizer were added at the rate of 29.6 cc per pot. Measurements taken were plant height, top fresh weight, root fresh weight, and root development. ANOVA was used to determine differences and interactions. Significant differences were noted in plant height and root development.

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M. Tagliavini and N.E. Looney

Root and shoot growth of peach seedlings was strongly suppressed when the roots were held at 8 to 10C. Shoot and root dry weights and root volume increased linearly with increasing root-zone temperature (RZT) to 22C. GA3 at 5.7 μm (2 ppm) added to the aerated full nutrient solution reversed the effect of low RZT on shoot elongation but inhibited root growth at all RZTs. Paclobutrazol (PBZ) (6.8 × 10-3μm) (2 ppb) inhibited shoot elongation at all RZTs and shoot dry weight at 16 and 22C. However, PBZ had no effect on root dry weight accumulation at any RZT. The shoot growth-promoting effect of GA3, relative to control plants, disappeared at higher RZTs, but GA3 reversed the growth-inhibiting effect of PBZ at all RZTs. PBZ increased mean root diameter at all RZTs and significantly increased root volume at 22C. These results show that growth of peach seedlings is profoundly influenced by a cool root-zone environment. The plant growth regulator effects suggest that seedling roots play an important role in whole-plant gibberellin physiology. Some possible implications for fruit production are discussed. Chemical names used: gibberellic acid (GA3); β -[(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol(paclobutrazol,PBZ).

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Shufu Dong, Lailiang Cheng, and L.H. Fuchigami

The nutrient uptake kinetics by new roots of 1-year-old potted clonal apple rootstocks (M7, M9, M26, M27, MM106, and MM111) were determined by the ion depletion technique at the stable development stage of trees in August. The total roots of five of the rootstocks (except MM111) consisted of more than 60% feeder roots and less than 12% extension roots. MM111, the most vigorous rootstocks tested, had 60.7% feeder roots and 24.5% extension roots. Root: top ratio was negatively related to the growth inhibiting character of the rootstock. Nutrient uptake by excised new roots was found to fit into Michaelis-Menton kinetic model for all rootstocks tested. The kinetic characteristics (maximum uptake rate, Imax, apparent Michaelis-Menton constant, Km, and root absorption power, (α = Imax•1/Km) between rootstocks differed significantly. MM111 had the highest Imax for NH4 + absorption and M9 for NO3 -. Root affinity to ions was highest with MM106 for NH4 + and with M26 for NO3 -. Root absorption power (α = Imax•1/Km) was greatest in MM106 for NH4 + and M9 for NO3 -. At this developmental stage the data suggest no relationship between nutrient uptake and dwarfing character of the rootstocks.

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Allen V. Barker and Kenneth A. Corey

Urea fertilization of `Heinz 1350' tomato (Lycopersicon esculentum Mill.) in sand or soil culture did not enhance ethylene evolution or restrict growth relative to plants receiving \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathbf{NO}_{\mathbf{3}}^{\mathbf{-}}\) \end{document} whereas \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathbf{NO}_{\mathbf{4}}^{\mathbf{+}}\) \end{document} nutrition doubled the relative rates of ethylene evolution and restricted relative growth. Inhibitors of N transformations in media (nitrapyrin, Np; hydroquinone, HQ; and phenylphosphorodiamidate, PPD) had no apparent stimulator effects on ethylene evolution of plants grown on urea or \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathbf{NO}_{\mathbf{3}}^{\mathbf{-}}\) \end{document} nutrition in sand or soil. Ethylene evolution was enhanced by PPD relative to that by Np or HQ for plants receiving \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathbf{NO}_{\mathbf{4}}^{\mathbf{+}}\) \end{document} nutrition. Each inhibitor had toxic effects on plant growth. Increasing K+ supply from 0 to 8 mm in nutrient solutions decreased ethylene evolution and increased plant growth with urea fertilization. Urea had low phytotoxicity if its hydrolysis to \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathbf{NO}_{\mathbf{4}}^{\mathbf{+}}\) \end{document} was prevented in the media. Chemical names used: p-dihydroxybenzene (hydroquinone); benzenephosphorodiamide (phenylphosphorodiamidate); 2-chloro-6-(trichloromethyl)pyridine (nitrapyrin).

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Matthew J. Fagerness, John Isgrigg III, Richard J. Cooper, and Fred H. Yelverton

Questions exist as to whether growth-inhibiting chemicals mimic the effects of reduced mowing heights on putting green ball roll. An experiment was initiated during Spring 1997 to investigate ball roll and visual quality parameters of putting greens maintained at 3.2, 4.0, or 4.8 mm with plant growth regulator (PGR) treatments applied monthly over the course of 1 year. Additional experiments were conducted during Fall 1995 and 1996 and Spring 1996 to investigate diurnal PGR effects on ball roll. All experiments were conducted on pure stands of `Penncross' creeping bentgrass (Agrostis palustris Huds). Treatments included trinexapac-ethyl and paclobutrazol, both inhibitors of gibberellin biosynthesis. In the one-year experiment, mowing height was inversely related to ball roll. However, compromises in turfgrass visual quality and shoot density in `Penncross' turf mowed at 3.2 mm make this a questionable mowing height in areas with severe summer conditions. Ball roll during summer months was reduced by PGRs, suggesting that PGRs have little potential as alternatives to decreasing mowing height for increased ball roll. Paclobutrazol reduced turfgrass quality and shoot density during summer months, suggesting that it be used with caution. Other PGRs, particularly trinexapac-ethyl at 0.05 kg·ha–1 a.i., increased afternoon ball roll by as much as 5% to 10% in diurnal experiments. Use of PGRs on creeping bentgrass putting greens may therefore produce short-lived increases in ball roll with subtle to negative effects on bentgrass growth over more extended periods of time. Chemical names used: 4-(cyclopropyl-α-hydroxymethylene)-3,5-dioxocyclohexane carboxylic acid ethylester (trinexapac-ethyl); (+/–)-(R *,R *)-β-[(4-chloro-phenyl)methyl]-α-(1,1dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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Pai-Tsang Chang, Marc W. van Iersel, William M. Randle, and Carl E. Sams

Dietary sources of selenium (Se) are associated with human health benefits, and Brassica species are good sources of Se in human diets. Selenium and S compete for absorption and accumulation in plant tissues; therefore, the ratios of Se to S in the growing environment determine the accumulation of selenium in plants. To determine responses for Brassica oleracea L., two levels of Na2SeO4 (96 mg·L−1 SeO4 2– and 0.384 mg·L−1 SeO4 2–) were added to nutrient solutions with or without MgSO4·7H2O (96 mg·L−1 SO4 2–). The highest plant fresh weight and S and SO4 2– accumulation were found when plants were grown in the medium with a SeO4 2– to SO4 2– ratio of 1 : 250 (0.384 mg·L−1 SeO4 2– and 96 mg·L−1 SO4 2–). However, the highest accumulation of Se was found when a low level of selenate (0.384 mg·L−1 SeO4 2–) was added to nutrient solutions without S. The activity of glutathione peroxidase (GPx) was regulated by Se status; the highest GPx activity was measured when a high level of SeO4 2– (96 mg·L−1) was supplied to nutrient solutions without S supplementation. The lowest concentration of total glucosinolates was found when adding SeO4 2– to nutrient solutions without S. We saw no difference in plant growth and mineral accumulation when plants were grown with K2SeO4 versus Na2SeO4, suggesting that the growth-inhibiting effect of Na2SeO4 was the result of the SeO4 2– rather than potentially toxic effects of Na+.

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Victor N. Njiti, Qun Xia, Leonna S. Tyler, Lakeisha D. Stewart, Antione T. Tenner, Chunquan Zhang, Dovi Alipoe, Franklin Chukwuma, and Ming Gao

plant growth inhibitors have been found to be effective in controlling vegetative growth, there are few without health and environmental concerns ( Miller, 2002 ). Prohexadione–calcium (calcium 3-oxido-5-oxo-4-propionylcyclohex-3-enecarboxylate) belongs