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Alvan Gaus and Matthew Rogoyski

The main objective of this research was to compare the growth responses of l-year-old, vertical, apple shoots to bending with a simple hand-tool (HT) or bending with the commercially available Branch Bender® (BB). Single, vigorous, vertical shoots of `Red Chief Delicious (RCD), `Valnur' Jonathan (VJ), and Granny Smith were either bent with the BB or were bent by spirally wrapping the shoot around a 2.5 cm diameter plastic-rod, HT 2 times. Each variety had nine single-tree blocks with a control, BB, and HT as treatments. Measurements were taken on the number of clusters formed, length of subsequent terminal growth, number of shoots and spurs formed, and shoot cross-sectional area. No differences were found in RCD between the BB and the HT on all parameters; however, terminal growth was less with the BB than the control. With VJ, first year shoot cross-sectional area for the BB was less than for the HT. Cluster formation on both 1 and 2-year-old wood was greater with the BB than the control but not with the HT. No differences were found with Granny Smith.

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Brent L. Black

Balancing vegetative growth with fruiting is a primary concern in strawberry (Fragaria ×ananassa Duch.) production. Where nursery plant selection and preconditioning are inadequate for runner control, additional approaches are needed. The gibberellin biosynthesis inhibitor prohexadione-Ca (commercial formulation Apogee) was tested over two seasons for suppressing fall runners of `Chandler' plug plants in a cold-climate annual hill production system. Prohexadione-Ca was applied as a foliar spray at active ingredient concentrations ranging from 60 to 480 mg·L-1, either as a single application 1 week after planting, or repeated at 3-week intervals. The lowest rate resulted in inadequate runner control, with some runners producing malformed daughter plants. Higher rates resulted in 57% to 93% reductions in fall runner numbers, with a concomitant increase in fall branch crown formation. There were no effects of the prohexadione-Ca treatments on plant morphology the following spring, and no adverse effects on fruit characteristics or yield. Chemical names used: prohexadione-calcium, calcium 3-oxido-4-propionyl-5-oxo-3-cyclohexene-carboxylate.

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Muntubani D.S. Nzima, George C. Martin, and Chic Nishijima

Early fall (September) defoliation and late spring (early June) shading of “off” and “on” pistachio trees were used to test two hypotheses: that 1) fall defoliation would reduce carbohydrate storage sufficiently to suppress spring growth and 2) spring shading would reduce carbohydrate status and increase inflorescence bud abscission. Defoliation suppressed initial leaf area expansion the following spring on current year shoots of “off” but not “on” trees respectively. Suppression of leaf size was correlated with the initial low concentration of carbohydrates in organs of individual branches of the tree. Fruiting and artificial shading in June had more dramatic effects on growth parameters than defoliating. Shading “off” trees for 14 days in early June accelerated abscission of inflorescence buds, reduced dry mass of individual leaves, buds, current year and 1-year-old shoots. Shading also reduced the concentration of total nonstructural carbohydrates (TNC) of these organs in “off” and “on” trees. Fruiting suppressed leaf size and leaf dry mass by 20% and 30% among individual branches of undefoliated and defoliated trees respectively. Low carbohydrate concentrations in individual branches and inflorescence buds following shading were closely correlated with the abscission of inflorescence buds.

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Zhi-Liang Zheng, Jyan-Chyun Jang, James D. Metzger, and Zhenbiao Yang

Plant architecture is a major consideration during the commercial production of chrysanthemum (Dendranthema grandiflora Tzvelev). We have addressed this problem through a biotechnological approach: genetic engineering of chrysanthemum cv. Iridon plants that ectopically expressed a tobacco phytochrome B1 gene under the control of the CaMV 35S promoter. The transgenic plants were shorter, greener in leaves, and had larger branch angles than wild-type (WT) plants. Transgenic plants also phenocopied WT plants grown under light condition depleted of far-red wavelengths. Furthermore, the reduction of growth by the expressed PHY-B1 transgene did not directly involve gibberellins. The commercial application of this biotechnology could provide an economic alternative to the use of chemical growth regulators, and thus reduce the production cost.

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Edward Bush, Jeff Kuehny, and Patricia Branch

Three slow-release fertilizer formulations (Osmocote 14–14–14, 18–6–12, and Nutricote 17–6–10) at three rates (1, 2, and 3 lb/yd3) were incorporated into 4 pine bark: 1 sand (by volume) media filling 1-gal nursery containers. Additional treatments included slow-release fertilizer formulations at 1 lb/yd3 fertigated with 100 ppm N 20–10–20 fertilizer. As fertilizer rates increased, vegetative height, width, and dry-weight accumulation generally increased for both pinched and no-pinch mum crops. Fertigated pinch and no-pinch mums were the largest plants with the greatest dry-weight accumulation for each fertilizer formulation. The high rate for all slow-release fertilizers produced the greatest vegetative growth for nonfertigated treatments. This research suggest that higher rates for incorporated slow-release fertilizers and/or fertigation are required to produce maximum vegetative growth.

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Jeff S. Kuehny, Blanca Morales, and Patricia Branch

Irrigation water quality is an important factor in ornamental plant production; however, there is little information in this area. Saline (NaCl) and alkaline (NaHCO3) water have been shown to cause general chlorosis, tip burn, and defoliation of plants. The growing medium used in crop production may be an important factor when irrigating with saline and alkaline water. Our objectives were to determine the effects of increasing concentrations of NaCl: CaCl2 and NaHCO3 in irrigation water on growth and development of spring and fall bedding plants grown in peat, peat/pine bark, and pine bark media. Plant dry weight, height, and width were significantly lower at 300 and 400 ppm NaCl: CaCl2 and NaHCO3 levels. Early visible symptoms were necrosis of leaf tips, some leaf discoloration and finally plant death in the NaCl: CaCl2 experiment. The leaves of plants in the NaHCO3 experiment became water soaked and chlorotic, and some leaf abscission occurred. The best plant growth in the NaHCO3 experiment occurred in peat and the best plant growth in the NaCl: CaCl2 experiment occurred in pine bark. Decreased uptake of K+, Ca++, and Mg++ occurred when high levels of sodium were present.

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Clare A. Bowen-O'Connor*, Rolston St. Hilaire, John Hubsten-berger, and Dawn VanLeeuwen

Bigtooth maple (Acer grandidentatum Nutt.) is indigenous to the southwestern United States. This species is not widely used in managed landscapes but the plant holds promise as a useful ornamental tree. Micropropagation might provide additional sources of selected genotypes for the nursery industry, but tissue culture has not been used successfully to propagate this species. We cultured double-node explants from greenhouse-grown, 2-year old seedlings of bigtooth maples that originated from Utah, Texas and New Mexico. Seedling height ranged from 15-90 cm. The shoot region was divided into three equal zones designated as terminal, intermediate and basal. Explants were selected from each of those zones. Explants were established on Murashige-Skoog (MS), Linsmaier-Skoog (LS), Woody Plant Medium (WPM) and Driver-Kuniyuki (DKW) tissue culture media. Shoot proliferation, area of the plate covered by callus and foliar pigment development (hue as determined by Royal Horticultural Society Color charts) were monitored for 17 weeks. Media affected shoot proliferation (P = 0.0042) but the zone of origin (P = 0.6664) of the explant did not. Callus area showed no significant difference among the four media and three zones (P = 0.2091) and averaged 3.60 centimeters2. After four subcultures, each lasting 30 days, explants on DKW media produced 10 shoots per explant. This media might hold promise for the micropropagation of bigtooth maple. Twenty-nine percent of all explants expressed foliar pigmentation, which ranged from red-purple to orange-red. Whether foliar pigment development in tissue culture correlates with expressed pigmentation in nature warrants further investigation.

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Jeff S. Kuehny, Aaron Painter, and Patricia C. Branch

Plug production has increased the finished quality and uniformity of bedding plants, making them one of the most important greenhouse crops grown. The wide range of cultural practices used by different growers to produce plugs, may influence the efficacy of plant growth regulators applied to the same crop in postplug production. Ten bedding plant species were grown from plugs obtained from two sources using different cultural practices. The plugs were transplanted to jumbo six packs and sprayed with either chlormequat/daminozide tank mix, ancymidol, or paclobutrazol at three concentrations at three times of year. The effect of each plant growth regulator varied by plant species and time of year applied. Source of plug material did have a significant effect on height and time of flowering of finished bedding plants and the use of plant growth regulators did not minimize the differences in height between sources in most cases.

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Jeff S. Kuehny, Wen Chy Chang, and Patricia Branch

Zantesdeschia has been grown for cut-flower production for many years, but more recently it has been grown as a containerized plant. Problems with height control and disease, however, have limited Zantesdeschia production in warmer climates. Our objectives were to evaluate paclobutrazol and uniconazole on control of plant growth of three Zantesdeschia species and evaluate four preplant treatments for preventing Erwinia infection on rhizomes. Paclobutrazol at 1 mg a.i. gave the best control of flower height, foliage height, and plant width. After 20 d in a postharvest chamber, plants drenched with paclobuturazol at 2 mg a.i. and uniconazole at 6 mg a.i. were still suitable plants, plants drenched at 3 and 4 mg a.i. paclobutrazol remained short, and plants drenched at 2 and 4 mg a.i.uniconazole became tall and weak, with flower stems breaking over. Rhizomes were dipped in dimethylbenzyl ammonium chlorides, sodium hypochlorite, 4% formaldehyde, or streptomycin. Streptomycin provided the best control against Erwinia infection followed by formaldehyde. Dimethylbenzyl ammonium chlorides and sodium chloride provided the poorest protection.