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An experiment was conducted to determine the influence of eight commercial root-zone media (four peat based and four pine bark based) on the effects of paclobutrazol applied to Euphorbia pulcherrima Willd. `Eckespoint Celebrate 2' as an impregnated spike or a drench. Paclobutrazol treatments had the least influence on stem elongation of poinsettias grown in the peat-based medium containing Bacctite, a compressed peat product designed to increase aeration and cation exchange capacity, or composted pine bark ground to a particle size that could pass through an opening 1 cm or smaller. Spikes were more effective at reducing shoot elongation than drenches. Spike treatments also resulted in lower bract dry-matter accumulation than drenches. Paclobutrazol applied as a spike to poinsettias at pinch could combine pinching and chemical growth regulator application into one simultaneous operation. Chemical name used: (±)-(R*,R*)-beta-[(4-chlorophenyl)methyl]-alpha-(1, 1,-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol).

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The response of Antirrhinum majus (snapdragon) cultivars (`Tampicoi' and `Rainier White') to night air temperatures (10C and 20C) and elevated root-zone temperature (26C and ambient) was studied. Height of plants grown with a heated root-zone were greater, compared to unheated at both night temperatures for both cultivars. Shoot dry weight of `Tampico' plants was reduced by heated root-zone temperature at 20C night air temperature. Raceme length was greater with heated root-zone temperature compared to unheated at 10C night air temperature. Days to flower were shorter with heated compared to unheated root-zone at both night air temperatures for both cultivars. Stomatal diffusive resistance was greater on plants with unheated compared to heated root-zone temperature at 10C night air temperature for `Rainier White'.

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Most field production of woody ornamental plants involves clean cultivation of rows, performed by either mechanical or chemical means. Grass cover has been shown to reduce erosion, but may have a detrimental effect on the growth and vigor of young trees. Clover cover has been shown to not adversely affect plant growth. The objective of this study was to compare the relative merits of three row covers, clean cultivated, pine bark mulch and kobe lespedeza clover, in combination with two irrigation rates, low and high, on field-grown red bud and crape myrtle plants.

Crape myrtle and red bud plants were tallest and had a larger caliper when grown with a clean row or with pine bark mulch. Kobe lespedeza clover reduced plant growth of both species when supplemental irrigation was not provided. Clover reduced plant height and caliper of red bud even when irrigated. Generally, plants grown under pine bark mulch were more efficient in water use as shown by greater stomatal conductance in August.

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Various uniconazole (Sumagic™) rates were either sprayed or drenched alone or in combination with 6-BA and GA4+7 (Promalin™) or dikegulac-sodium (Atrinal™) on Hibiscus rosa-sinensis `Brilliant'. The rates of uniconazole were 0, 5, 10, and 15 mg a.i./L; 6-BA and GA4+7, 25 mg a.i./L each; and dikegulac-sodium 1000 mg a.i./L.

Plant height was reduced by uniconazole when drenched at rates as low as 5 mg/L and 15 mg/L when sprayed. Dikegulac-sodium slightly counteracted the effects of uniconazole. Uniconazole activity was increased when either sprayed or drenched with application of 6-BA and GA4+7 resulting in greater height reduction.

Transpiration and stomatal diffusive resistance of plants drenched with uniconazole alone was erratic; however, when uniconazole was sprayed or drenched and mixed with 6–BA and GA4+7 or dikegulac-sodium transpiration increased.

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Abstract

The design for a chamber to control high root-zone temperature is presented. Air within the insulated chamber was heated with vinyl-jacketed heating cables and cooled with 1:1 water and antifreeze (v/v) pumped through copper coils. Control of the soil temperature was based upon air temperature around the soil containers within the sealed chambers. Chamber operating temperatures could be held between 20° and 50°C ± 0.2° SE.

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Abstract

High root-zone temperatures can stress container-grown plants and ultimately reduce nursery productivity in the southern United States. Water relations of glasshouse-grown Berberis thunbergii DC ‘Atropurpurea’ Buxus microphylla Seibold and Zucc japonica and Pittosporum tobira, (Thunb.) Ait. ‘Wheeler’ were studied under high-temperature root-stress conditions using container-grown plants that were either colonized with vesicular arbuscular mycorrhizal fungi (VAM) or noncolonized. Predawn xylem water potential in stems (ψstem) increased initially (more positive) in response to high root-zone temperatures (40° to 45°C), and then decreased over a 5-day period. Stomatal conductance (gs) and evapotranspiration (ET) were reduced incrementally over time in response to high root-zone temperatures. Root damage occurred, as indicated by reductions in root quality and gs at 35° and 40° for B. thunbergii and P. tobira, and at 40° and 45° for the more high-temperature-resistant B. microphylla. Colonization increased gs and ET of B. microphylla at ambient (25°) and high temperatures (45°) and increased ET of B. thunbergii at 25°. Colonized plants had lower (more negative) ψshoot with initial exposure to increased root-zone temperatures; however, throughout the remainder of the study period there was little reduction in plant stress with the mycorrhizal isolates used. Root hydraulic conductivity (Lp) increased markedly in B. thunbergii compared to B. microphylla at 40° and 45°, indicating less high-temperature resistance in B. thunbergii roots. Mycorrhizal colonization did not moderate hydraulic conductivity at high root-zone temperatures of 40° and 45°. Of the two species, mycorrhizal B. thunbergii had lower Lp at 25° and B. microphylla had lower Lp at 35°.

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Leaflet surfaces of two blackspot (Diplocarpon rosae Wolf)-resistant roses (Rosa roxburghii Tratt and R. wichuraiana Crep.) and two susceptible roses (R. hybrida `Electron' and `Pascali') were compared using scanning electron microscopy to determine whether physical features of the leaflet surface were associated with resistance to the fungal invasion. The leaflet surface features of the resistant roses were dissimilar: R. roxburghii leaflet surface had protruding cells and was densely covered with amorphous wax platelets, whereas R. wichuraiana surface was smooth with less distinct epidermal cells and sparsely distributed wax granules. Leaflet surface patterns of both susceptible roses, however, were similar. The spores of D. rosae failed to germinate on R. roxburghii and R. wichuraiana. In contrast, the spores on `Electron' and `Pascal? germinated, with the germ tube penetrating the cuticle. There were no apparent morphological barriers on leaflet surfaces of R. roxburghii and R. wichuraiana to explain the observed resistance to fungal development.

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Uniconazole has been demonstrated to not only reduce plant height, but suppress the development of xylem and phloem in stem tissue. Supplemental calcium nutrition in poinsettias has been demonstrated to reduce marginal bract necrosis, reduce leaf puckering and increase stem strength. Studies were conducted to determine the influence of uniconazole on Gutbier V-14 Glory poinsettias grown with supplemental calcium applied either as a foliar spray or a media drench.

Supplemental calcium applications improved the growth habit of uniconazole treated poinsettia plants. Bract coloration was intensified by foliar applications of calcium and uniconazole.

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Poinsettias and other floral crops when treated with the growth retardant uniconazole, Sumagic™, are more compact in growth habit. They have also been shown to have reduced stem strength. Calcium applied as a drench has been demonstrated to increase plant height and plant dry weight of poinsettias. Unicomazole reduced plant height without affecting dry weight. Bract color was more intense when calcium was applied as a weekly spray. Poinsettia plants had greater levels of foliar calcium when applied as a drench. Poinsettia plants sprayed and drenched with calcium and treated with uniconazole had greater levels of foliar calcium, however, this was not significantly greater than the control plants treated with uniconazole alone. The lowest level of foliar calcium was observed in uniconazole treated plants where calcium was applied as a spray. Uniconazole applications weakened the stein structure of poinsettias as with other floral crop species.

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The objective of this study was to determine the influences of 8 commercial media, 4 peat-based and 4 pine bark-based, on the effects of paclobutrazol and uniconazole applied as a media drench to `Gutbier V-14 Glory' poinsettias. The peat-based media were Baccto Grower's Mix, Baccto High Porosity Professional, Baccto High Porosity Professional with Bacctite, and Baccto Rockwool Mix. The pine bark-based media were Metro 360, 366, 700, and 702. Paclobutrazol and uniconazole were each applied to plants grown in each media at 5 rates (0, 0.125, 0.250, 0.375, and 0.500 mg·15 cm pot-1). Paclobutrazol and uniconazole effectively reduced plant height in all media. Plants grown in the Metro products, however, tended to be larger than those grown in the Baccto products. Plants grown in the peatbased media were more sensitive to growth regulator drenches. Plants grown in Metro 360 and 366 were the least sensitive to plant growth regulator drenches compared to the Baccto media.

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