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Mark Rieger and Giancarlo Scalabrelli

Paclobutrazol (PBZ) was supplied in nutrient solution culture to `Nemaguard' peach rootstock [Prunus persica × P. davidiana] at concentrations of 0, 0.001, 0.01, 0.1, and 1.0 mg·liter-1. PBZ increased root: shoot ratio and decreased root length by ≈ 5-fold over the range of PBZ concentrations tested. Root tip diameter, stele diameter, and width of the root cortex were not significantly affected by PBZ. Root hydraulic conductivity decreased log-linearly with increasing PBZ concentration; however, this decrease did not affect midday leaf conductance or net photosynthetic rate. Foliar levels of N, P, K, Fe, and Mo were reduced, whereas levels of Ca, Mg, B, and Mn were increased by PBZ. The magnitude of changes in foliar nutrition were proportional to the degree of growth suppression. Chemical name used: (2RS,3RS)-l-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-ol (paclobutrazol).

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Fouad M. Basiouny and Floyde M. Woods

Applications of paclobutrazol (PP333), Daminozide (DZ), and Nutri-cal to rabbiteye blueberry (Vaccinium ashi Reade) was studied. The application of these chemicals at different concentrations was made in the fall and throughout the growing season. PP333, DZ and Nutri-cal induced variable effects on yield, inte rnal and external fruit qualities. Shelf-life of hand-harvested fruits responded favorably to each of these chemicals.

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Yin-Tung Wang and Thomas M. Blessington

Uniconazole and paclobutrazol were tested for their effects on greenhouse production of four foliage species. Soil drenches of uniconazole retarded shoot and petiole elongation of Brassaia actinophylla Endl. Paclobutrazol reduced shoot elongation, but required higher doses than uniconazole and did not reduce petiole growth. Foliar sprays with either retardant at 12.5 mg·liter-1 resulted in short stems on lateral shoots of Codiaeum variegatum (L.) Blume `Karen' after pinching, but soil drenches at low rates were less effective. Soil drenches of uniconazole or paclobutrazol were equally effective in reducing stem growth of Syngonium podophyllum Schott `White Butterfly' and increasing leaf width, but had no effect on the rate of leaf production or blade length. Both retardants induced short petioles in this species. Severe growth reduction occured on Plectranthus australis R. Br. even at the lowest rates of uniconazole and paclobutrazol (0.025 and 0.20 mg/pot, respectively) as soil drenches. Production of lateral shoots was inhibited for P. australis by both retardants. Chemical names used: (E)-1-(p-chlorophenyl)-4,4-dimethy1-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazole); (2RS,3RS)-1-(4-chlorophenyl)-2-(1,1-dimethylethyl)-(H-1,2,4-triazol-l-Yl-)Dentan-3-ol (paclobutrazol).

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R.I. Wilkinson and B. Hanger

Miniature flowering potted Hydrangea macrophylla Thunb. cv. Merritt's Supreme plants (multistem, 15 to 20 cm tall) were grown in a modified hydroponic system. High-quality plants were produced by pulsing plants with paclobutrazol (0.2 mg·liter-1) for 4 weeks. Flower initiation was advanced in the terminal buds of treated plants by 12 days, and this earlier flower development was maintained through to flower maturity, without loss of inflorescence diameter. Chemical name used: β -[(4-chlorophenyl) methyl] -α-(1,1-dimethylethyl)-1 H -1,2,4-triazole-1-ethanol (paclobutrazol, ICI-PP333).

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R.I. Wilkinson and D. Richards

Shoot extension of Rhododendron `Sir Robert Peel' was reduced, but flowering was more precocious after treatment of plants with paclobutrazol. All of the drench rates tested (0.05 to 0.4 g a.i./pot) proved excessive and resulted in prolonged shoot growth reduction but greatly increased the number of flowers. However, flowers produced at the higher drench rates were grossly malformed and unacceptable. Foliar spray treatments (250 to 2000 mg a.i./liter) were less inhibitory than drenches, and a single spray of 500 mg·liter-1 was considered an appropriate commercial application rate. Paclobutrazol application could thus prove to be a useful technique in producing compact flowering plants of Rhododendron hybrids for improved retail sales. Chemical name used: β-[(4∼chlorophenyl) methyl] (1,1-dimethylethl)-1H-l,2,4-triazole-l-ethano1 (paclobutrazol, ICI-PP333).

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Hsin S. Lin and Chin H. Lin

High-chilling pear cv. Shinseiki (Pyrus serotina Rehd.) were used to evaluate the cultivation potentiality at warm area via the decrement of supraoptimum temperature damage and the escape from dormancy. Several experimental results were obtained as follows: the media prepared by combination of peat and bark compost (1:1 in volume) inside nonwoven bag was lower in temperature than other media; both of the temperature of leaf surface and media decreased more than 2′C at noon by 25% shading favoring the CO2 exchange in the daytime; the foliage application of Aminofol increased leaf thickness and chlorophyll content; and BA or PP-333 treatment enhanced lateral buds development during the supraoptimum temperature period of summer, etc. An integrated management based on these results helped the 1-year old container-grown Shinseiki pear trees over-summer. The experimental trees were then forced to budbreak and flower by application of cyanamide in October. Eventually, the fruits were harvested in March. These results suggested that the production of high-chilling pears in warm area was technically feasible.

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Mark K. Ehlenfeldt

Blueberry cultivars were treated with either soil drenches or foliar applications of paclobutrazol. Soil drenches of 25 mg·L-1 inhibited shoot elongation and stimulated earlier and greater flower bud production on `Bluetta', `Bluecrop', and `Jersey'. The treatments increased bud numbers 359% to 797%, and stimulated compound bud formation, while reducing formation of vegetative buds. This resulted in overcropping and reduced fruit size. Foliar applications at concentrations of 5, 10, 50, and 100 mg·L-1 increased bud set. Treatments did not significantly alter time to 50% flowering in `Bluecrop' or `Duke', but hastened flowering up to 5 days in `Blueray' at 200 ppm. Fruit ripening was significantly delayed at 100 and 200 ppm in `Bluecrop' due to overcropping, but no delays were observed in `Blueray' or `Duke'. Plant size and vigor appeared to be a determining factor in plant response. Chemical name used: PP333 or (2RS,3RS)-l(4-chlorophenyl)-4,4-dimethyl-2-(l,2,4-triazol-1-yl)pentan-3-ol (paclobutrazol).

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Anwar A. Khan and Claudinei Andreoli

Dormancy was induced in nondormant (germinate readily in light or darkness) seeds of several lettuce cultivars (Mesa 659, Emperor, Empress, Montello, Ithaca) by soaking in the dark in 5-100μM tetcyclacis (TCY) for 24h at 25°C as the seeds failed to germinate in the dark upon removal of TCY by washing. Higher concentrations of TCY was needed to induce dormancy in the light Paclobutrazol (PP 333) was relatively less effective. No dormancy was induced in nondormant lettuce seeds soaked for 24h in 100μM ABA as the seeds germinated readily in the dark upon removal of the inhibitor by washing. Thus, contrary to popular belief ABA does not appear to be a dormancy factor. Dormancy induced by TCY was released by soaking seeds in petri plates in water at 25°C in the light, in the presence of 0.001-1mM GA4+7, or by moist-chilling for 4-15d at 5°C. Dormancy was also released when dried dormant (dormancy induced by TCY) Mesa 659 or Emperor lettuce seeds were planted in a moist peat-lite mix in plastic containers and kept moist for 30d at 5°C, as indicated by emergence of normal, healthy seedlings upon transfer of the containers to 25°C. The significance of TCY induced dormancy in altering planting strategy in field plantings of lettuce and other crops will be discussed.

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Haijun Zhu and Eric T. Stafne

837 839 Wood, B.W. 1986 Influence of paclobutrazol (PP-333), Flurprimidol (EL-500) and Ortho XE-1019 (Chevron) growth retardants on growth and selected chemical and yield characteristics of Carya illinoinensis Acta Hort. 179 287 288 Wood, B.W. 1987

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Christopher J. Currey, Diane M. Camberato, Ariana P. Torres, and Roberto G. Lopez

control by ancymidol, PP333, and EL500 dependant on medium composition HortScience 17 896 897 Barrett, J.E. 2001 Mechanisms of action 32 41 Gaston M.L. Konjoian P.S. Kunkle L.A. Wilt M.F. Tips on regulating growth of floriculture crops OFA Services