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Daniel C. Bowman, Richard Y. Evans, and Linda L. Dodge

A study was conducted to determine the potential for using ground automobile tires as a container medium amendment. Rooted cuttings of chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura] were planted in 1.56-liter pots containing 1 sand:2 sawdust (v/v) or media in which coarsely or finely ground particles of rubber substituted for 33%, 67%, or 100% of the sawdust. Amendment with the coarse material decreased total porosity and container capacity and increased air-filled porosity and bulk density relative to the sawdust control. Amending the medium with the fine material did not appreciably alter total porosity, container capacity, or bulk density, but did increase air-filled porosity. Plant height, fresh weight, dry weight, and number of open flowers were reduced significantly in rubber-amended media compared to sawdust controls. Rubber amendment reduced shoot tissue concentrations of N, P, K, Ca, Mg, and Cu, but increased Zn as much as 74-fold over control values. There was no accumulation of other heavy metals (Cd, Cr, Ni, Pb) or Na in the tissue due to rubber amendment. This study demonstrates that ground tires might be used as a component of container media in the production of greenhouse chrysanthemums. However, growth reductions and the potential for Zn toxicity may limit the usefulness of ground tires as a substitute for conventional organic amendments.

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Nihal C. Rajapakse and John W. Kelly

Transpiration rates of chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] plants grown under spectral filters were evaluated as part of an investigation on using light quality to regulate plant growth. The 6% CuSO4·5H2O spectral filter reduced photosynthetic photon flux density in red (R) and far red (FR) wavelengths and increased the R: FR and blue (B): R ratios (B = 400 to 500 nm; R = 600 to 700 nm; FR = 700 to 800 nm) of transmitted light relative to the water (control) filter. After 28 days, cumulative water use of plants grown under CuSO4 filters was ≈37% less than that of control plants. Transpiration rates were similar among plants grown under CuSO4 and control filters when expressed as leaf area, a result suggesting that the reduced cumulative water loss was a result of smaller plant size. Plants grown under CuSO4 filters had slightly lower (10%) stomatal density than control plants. Light transmitted through CuSO4 filters did not alter the size of individual stomata; however, total number of stomata and total stomatal pore area per plant was ≈50% less in plants grown under CuSO4 filters than in those grown under control filters due to less leaf area. The results suggest that altering light quality may help reduce water use and fertilizer demands while controlling growth during greenhouse production.

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Kimberly A. Williams and Paul V. Nelson

Soilless substrates have little capacity to sorb PO4. One way to reduce PO4 leaching during production is to increase the substrate retention of PO4. Adsorption isotherms were created at 25 C for alumina (aluminum oxide); the 2:1 calcined clays arcillite (montmorillonite plus illite) and attapulgite.; and a medium of 70 peat: 30 perlite using solutions of KH2PO4 at rates of P ranging from 0 to 20000 μg·ml-1. Material sorbed at the rate resulting in maximum P adsorption was then desorbed 22 times. Sorbing concentrations necessary to establish an equilibrium P concentration of 10 μg·ml-1 in the substrate solution were estimated from these curves. Materials were-charged with P at these estimated rates and evaluated in a greenhouse study in which each material was tested at 10 and 30% by volume of a 70 peat: 30 perlite substrate used to produce Dendranthema × grandiflorum `Sunny Mandalay'. Phosphate, K, and pH were determined on unaltered soil solutions biweekly throughout the cropping cycle and foliar analyses were determined on tissue collected at mid- and end-crop. Isotherm and greenhouse data indicated that alumina, arcillite, and attapulgite effectively retained and slowly released K as well as PO4 over time. Alumina was most effective at retaining P, sorbing 16800 μg/cc compared to 3100 and 7800 μg P sorbed/cc for arcillite and attapulgite, respectively, when sorbed at P concentrations resulting in an equilibrium concentration of approximately 10 μg P/ml.

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Sorua L. Maki, Melissa B. Riley, and Nihal C. Rajapakse

Endogenous gibberellins of chrysanthemum [Dendranthema ×grandiflorum (Ramat)] cv. Bright Golden Anne were characterized in apices from plants grown under control and CuSO4 spectral filters. Expanding shoots were separated into young expanding leaves and apices. Methanolic extracts of young expanding leaves were purified by solvent partitioning, PVPP column chromatography and reversed-phase high performance liquid chromatography. Two bioactive regions corresponding to the HPLC retention times of GA1 and GA19 standards were detected in fractions using the recently-developed non-dwarf rice bioassay. Di-deuterated internal standards of GA12, GA53, GA19, GA20, and GA1 were added to similar extracts of shoot apices. The presence of endogenous GA53, GA19, GA20, and GA1 in chrysanthemum apices was confirmed by isotope dilution using gas chromatography-mass spectrometry-selected ion monitoring and Kovats retention indices. In a preliminary quantification study, GA20 and GA1 levels were found to be higher in apices from plants grown under control filters while GA19 levels were higher in apices grown under CuSO4 filters. The possibility that light transmitted through CuSO4 filters alters gibberellin levels in shoot apices is discussed.

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Richard K. Schoellhorn, James E. Barrett, and Terril A. Nell

Effects of photosynthetic photon flux (PPF) and temperature on quantitative axillary budbreak and elongation of pinched chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] plants were studied in three experiments. In Expt. 1, 12 commercial cultivars were compared under fall and spring environmental conditions. Spring increases in lateral shoot counts were attributable to increased PPF and air temperature. Cultivars varied from 0 to 12 lateral branches per pinched plant and by as much as 60% between seasons. There was a linear relationship between lateral branches >5 cm at 3 weeks after pinching and final branch count (y = 0.407 + 0.914(x), r 2 = 0.92). In Expt. 2, air was at 20 or 25C and the root zone was maintained at 5, 0, or –5C relative to air temperature. With air at 20C, lateral branch counts (3 weeks after pinch) declined by ≤50% with the medium at 15C relative to 25C. At 25C, lateral branch count was lower with medium at 30C than at 20C. Cultivars differed in their response to the treatments. Experiment 3 compared the interactions among temperature, PPF, and cultivar on lateral branch count. Depending on cultivar, the count increased the higher the PPF between 400 and 1400 μmol·m–2·s–1. Air temperature had no effect on lateral branch count. PPF had a stronger effect on lateral branch count than air temperature, and cultivars differed in their response.

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William R. Graves and Hongyi Zhang

Air temperature and photosynthetically active radiation (PAR) effects on relative water content (RWC), rooting percentage, root count, and root mass of unmisted, subirrigated stem cuttings of two taxa were determined. Leaf RWC of `Charm' chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] decreased until roots initiated and then increased, was lower for cuttings at 23 °C photoperiod/14 °C dark than for cuttings at 31 °C photoperiod/22 °C dark, and was lower at 193 than at 69 μmol·m–2·s–1 PAR. Neither temperature nor PAR affected leaf RWC of `Dollar Princess' fuchsia (Fuchsia ×hybrida Hort. ex Vilm.), which increased linearly before and after root initiation. Rooting percentage and root count were higher with photoperiods at 31 °C than at 23 °C for chrysanthemum after 7 days and for fuchsia after 10 days. Although all cuttings of both taxa had rooted after 14 days, root dry mass was higher with photoperiods at 31 °C than at 23 °C regardless of PAR for fuchsia and at 69 μmol·m–2·s–1 PAR for chrysanthemum. Propagators wishing to use subirrigation instead of mist, fog, or enclosure can minimize the decline in leaf RWC before root initiation and increase the number and dry mass of roots of chrysanthemum by using 69 μmol·m–2·s–1 PAR and a 31 °C photoperiod/22 °C dark cycle. Root dry mass of fuchsia also can be increased by the use of high temperature, but differences in rooting were independent of changes in leaf RWC.

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C.J. Catanzaro and R.J. Sauve

A greenhouse study was conducted in Autumn 1998 using standard cultural practices for potted chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura] to determine how fertilization affected plant growth and quality and nutrient leaching. Fertilization treatments included constant liquid fertilization until anthesis (LFA), constant liquid fertilization until disbud (LFD), slow-release resincoated fertilizer (SRF), and no-fertilizer control. Frequency of irrigation was determined gravimetrically, and leaching fractions maintained near 0.2. Plant growth and quality for LFA, LFD, and SRF met commercial crop standards. Nearly 60% of the total nitrogen applied with LFA was applied during the 4 weeks between disbud and anthesis, due to increased water demand. During the same period when liquid fertilization was discontinued for LFD, leachate electrical conductivity (EC) levels dropped from 4 to <1 dS·m-1. Leachate EC levels for LFA at anthesis remained high, but were <1 dS·m-1 for the other treatments. LFD and SRF drastically reduced the total amount of nutrients applied during the course of production compared with LFA. Use of an appropriate slow-release fertilizer or discontinued use of liquid fertilizer at disbud allow soluble salt levels to decrease during the latter weeks of the mum production cycle, when nutrient demand is low and water demand is high.

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Richard J. McAvoy*, Mariya V. Khodakovskaya, Hong Liu, and Yi Li

Cytokinins play an important role in regulating plant growth and development. The cytokinin gene, isopentenyl transferase (ipt), was placed under the control of the ACC oxidase promoter from the LEACO1 gene from Lycopersicon esculentum and introduced into Nicotiana tabacum (cv. Havana) and chrysanthemum (Dendranthema × grandiflorum `Iridon'). Transformants were confirmed by PCR reaction and Southern blot and analyzed for phenotypical changes under both greenhouse and growth chamber conditions. With both species, LEACO1-ipt transgenic plants displayed a wide range of vegetative and generative phenotypes. With plants growing in the vegetative state, some LEACO1-ipt transgenic lines appeared similar to the non-transgenic wild-type cultivars while other lines showed excessive lateral branch development and short internodes. With plants grown under generative conditions, several LEACO1-ipt transgenic lines showed a 2 to 10-fold increase in the number of flower buds relative to the wild-type cultivars. With chrysanthemum, dramatic increases in bud count were observed on transgenic lines that otherwise displayed a morphology similar to the non-transgenic lines. Analysis of ipt expression indicated a marked change in gene expression between the most extreme phenotypes observed in this study. LEACO1-ipt lines that express normal vegetative development but increased flower bud counts appear to have great potential for ornamental crop improvement.

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Chun Ho Pak, Seung Won Kang, and Chiwon W. Lee

Efficacy of application methods and concentration of plant growth retardants on growth of chrysanthemum (Dendranthema ×grandiflorum cv. Cheasepeake) was tested. B-9 or cycocel (CCC) as a growth retardant was applied as drench or subapplication with nutrient solution. In the case of B-9 drench treatments, as B-9 concentrations increased, numbers of flowers and flower buds increased except in the 1500-ppm treatment. Increasing concentration of CCC also resulted in reduction of flower numbers, total plant height, total leaf area, branch number, and fresh weight. Reduction ratio of total plant height in 2000 ppm showed about 56.9% being compared to that of the 100-ppm drench treatment. B-9 or CCC, combined with nutrient solution, was also supplied from the C-channel subirrigation system. The B-9 subapplication treatment showed no significance among these concentrations, but flower numbers, total plant height, average plant height, and leaf numbers decreased as concentrations of CCC increased. B-9 or CCC with the same concentration was drenched after 2 weeks of the first experiment to compare planting time efficacy. Measured data increased until B-9 increased up to 2500 ppm and severe growth retardation resulted from the 5000-ppm treatment. Through this growth retardant application study, the combination of drenching concentration and period of plant growth regulators (PGRs) may result in effective growth retardation and reduction of application concentrations for pot plant production.

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Yeun Joo Huh, Seoung Youl Choi, Hak Ki Shin, and Chun Ho Pak

Nonbranching chrysanthemums [Dendranthema × grandiflorum (Ramat.) Kitamura] are preferred because they require less labor in disbudding. High temperature is responsible for this phenotype of not having axillary buds or poor lateral shoot development. This study attempted to find out the effect of temperature and identify the involvement of endogenous polyamine contents in axillary bud formation of nonbranching chrysanthemum cv. Iwanohakusen. Plants were treated at 22, 26, 30, 34, and 38 °C for 9 hours midday for 2 months. Polyamine content [putrescine (Put), spermidine (Spd), spermine (Spm)] was analyzed 1 month after treatment and axillary buds were counted when the flowers opened. Results revealed that viable axillary buds decreased remarkably at 30 and 34°C. It was also found out that not only low temperature, but also the excessively high temperature of 38 °C induced axillary bud formation. Exposure to 38 °C increased the Put contents and resulted in high Put/(Spd + Spm) ratio as 22 °C, 26 °C. Temperature of 30, 34 °C lowered Put/(Spd + Spm) ratio. Results further showed that not polyamine contents, but polyamine ratio (Put/Spd + Spm) or transformation of Put to Spd and Spm may be involved in the axillary bud formation in nonbranching chrysanthemum.