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Joseph J. King, Lloyd A. Peterson, and Dennis P. Stimart

Ammonium and NO3 uptake from hydroponic solutions containing 1 mm each of (NH4)2SO4 and Ca(NO3)2 were measured during development of Dendranthema ×grandiflorum (Ramat.) Kitamura `Iridon', `Sequoia', and `Sequest'. Nitrogen depletion from solutions approximated a 1 NH4: 1 NO3 ratio throughout a 90-day growth cycle (r = 0.96). Although harvest date cultivar interactions were significant for both forms of N, overall patterns of N uptake were similar among cultivars. Nitrogen removal from hydroponic solutions (milligrams per plant) was greatest from days 40 to 60; however, N removal (milligrams per gram of tissue dry weight) was greatest in the first month of development and decreased steadily until day 90. From day 40 to 60, new leaf development ceased while inflorescence buds developed to ≈1.0 cm in diameter. After this time, N uptake decreased rapidly as inflorescences expanded. Correlations between morphological changes and N demand could maximize the efficiency of applied N by matching form and application timing with plant needs.

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

Effects of heat stress on viable and nonviable axillary meristem development and subsequent lateral branching in 'Improved Mefo' chrysanthemum [Dendranthema ×grandiflorum Ramat. (Kitamura)] were studied. Plants grown at 33 °C day/27 °C night produced more nonviable buds than did plants grown at 23 °C day/18 °C night. A negative linear relationship {y = 28.7 + [-0.66 (x days)], r 2 = 0.70} between timing of exposure to high temperatures and the number of nonviable buds was observed. Histological examination 28 days after exposure to 33 °C/27 °C revealed that plants showed both normal and abnormal bud development. Abnormal bud development occurred as a consequence of premature differentiation of axillary meristematic tissue into nonmeristematic parenchyma tissue immediately after separation of axillary from apical meristems.

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Nihal C. Rajapakse, David Wm. Reed, and John W. Kelly

Experiments were conducted to evaluate Dendranthema × grandiflorum (Ramat.) Kitamura cv. Bright Golden Anne quality and post-storage growth following storage in the range of 5 to 35C, initial soil water levels (60%, 80%, 100%), and durations (0 to 8 days). Transpiration rate showed a quadratic relationship with storage temperature. Initial soil water content had little effect on transpiration rate in dark storage environments. The lowest transpiration rate was observed in plants stored at 15 or 20C. Amino acid (AA) leakage and post-storage growth were well-correlated. Plants stored at or above 25C became etiolated during storage, while storage at 15C or below did not cause etiolation. Temperatures at or below 15C did not affect subsequent growth rate of chrysanthemum plants. Storage at 20C and above caused a reduction in post-storage growth rate following 2 days of storage.

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Jason R. Tutty, Peter R. Hicklenton, David N. Kristie, and Kenneth B. McRae

Stem elongation rate (SER) in Dendranthema grandiflorum (Ramat.) Kitamura was determined in light and in darkness under various temperature regimes. Stem growth as measured with linear voltage displacement transducers on plants in growth chambers. Under alternating 11-hour days and 13-hour nights, SER was strongly temperature dependent and showed patterns that were characteristic of the particular photoperiod-temperature regime under which the plants were grown. Total daily elongation was similar at constant 18.3C and at 11.5C days and 24C nights, but was much greater at 25.7C days and 12C nights. SER was rhythmic in continuous light with a period of slightly less than 24 hours. In continuous darkness, however, SER declined rapidly and the rhythm disappeared within 11 hours. Low-temperature pulses (a rapid decline from 18.3C to 8.3C) applied for 2, 4, 6, 8, or 11 hours during the day induced an immediate decline in SER followed by a slow recovery and peak shortly after the end of the pulse. Total diurnal stem growth declined with increasing pulse length, although short (2-hour) duration pulses apparently had little effect on growth. The results are discussed in relation to the influence of day and night temperature differentials (DIF) on stem growth in Dendranthema.

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H.F. Wilkins, W.E. Healy, and K.L. Grueber

For chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura], the hypothesis that a 12-hr 5C or 13C dark treatment could be used in conjunction with a 12-hr 27, 21, 17, or 13C light treatment for rapid flowering when applied during certain developmental stages was valid. Flowering of `Bright Golden Anne', planted on 23 Sept., was not delayed by 12-hr light/12-hr dark growth chamber treatments of 21/5C or 27/13C (day/night) if treated from planting (P) of the rooted cutting to the start of short days (SD), 3 weeks after start of SD to visible bud (VB) (SD + 3 to VB), or from VB to flower (F) when compared to the glasshouse control plants grown at 21/18C. Plants responded similarly if grown at 13/13C or 21/21C, but flowering was delayed compared to the 17/17C glass house control. Delays were absent, however, when 13/13C was used from P to SD, SD + 3 to VB, or when 17/13 or 21/13C was used from VB to F.

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M.J. McMahon, J.W. Kelly, D.R. Decoteau, R.E. Young, and R.K. Pollock

`Spears' (nonpinched and pinched) and `Yellow Mandalay' (pinched) chrysanthemums were grown in growth chambers equipped with panels filled with liquids that served as spectral filters. Light quality was altered by reducing blue light, increasing red: far-red (R: FR) light, or reducing R: FR. Control panels did not selectively alter light transmission. Photosynthetic photon flux was the same in all chambers. All plants grown under increased R: FR filters had reduced height, reduced internode length, and increased chlorophyll content compared to controls. Reduction in blue light decreased chlorophyll content of pinched plants compared to controls. Pinched plants grown under increased R: FR light and !ong days developed fewer nodes than controls due to the formation of abnormal capitula; the controls and plants from the other treatments developed more nodes before producing similarly abnormal capitula. Stem diameter and leaf area did not differ due to treatments.

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Kiffnie M. Holt and Paul H. Jennings

Rooted chrysanthemum cuttings of five cultivars were transplanted into 6 1/2″ pots and greenhouse-grown for 7 weeks under natural daylength conditions. Plants were pinched back twice, on the 3rd week and the 5th week following transplanting. At 7 weeks, plants were arranged in a complete randomized-block design with four plants per cultivar per treatment and three replications. Spacing of the pots was kept constant through the duration of the experiment. The chemical group was sprayed with 2500 ppm B-Nine until run-off on the first day of treatment. The mechanical group was brushed 40 times, twice a day, for 5 weeks. The brushing mechanism was adjusted daily to account for growth so as to stimulate only the top 2 to 3 inches of the plant. Measurements of all plants were taken on the first and last day of the mechanical treatment. Data collected included height, internode length, and leaf area. Plants were then allowed to flower under the naturally shortening daylength, and the flowering date was recorded. The chemical and mechanically treated plants were shorter than the controls with a greater response occurring with the cultivars `Emily' and `Cheery Emily', which had a more open and upright growth habit. Cultivar response differences and effects on internode length, leaf area, and flowering date were noted and will be discussed.

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J.D. MacDonald

Cuttings of Dendranthema ×grandiflorum `Paragon' were used as a model system to assess the effects of root heating on disease severity. Roots were exposed to single episodes of heat stress, after which they were inoculated with zoospores of Phytophthora cryptogea Pethyb. & Laff. Root damage resulting from heat stress, or heat stress plus Phytophthora, was quantified 5 to 7 days after treatment. Roots of hydroponically grown plants, immersed for 30 min in aerated, temperature-controlled nutrient solutions, were severely damaged at 45C or above. Relatively little phytophthora root rot developed on inoculated plants exposed to 25 or 35C, but infection was severe in roots heated to 40C. Plants grown in potting mix were exposed to heat stress by plastic-wrapping the containers in which they were growing and placing them in heated water baths until roots achieved desired temperatures for 30 min. This system heated roots more slowly than in the hydroponic experiments, and 45 and 50C were less damaging. The amount of Phytophthora-induced root damage was insignificant in containerized plants heated to 25 or 35C, but was highly significant in those heated to 40C or higher. In field experiments, plants were positioned so their containers were either fulIy exposed to the late afternoon sun or heavily shaded to prevent sun exposure. The root zones of sun-exposed pots heated to 45 to 47C, while those of shaded pots never exceeded 34 to 36C. There was a large, highly significant increase in phytophthora root rot severity in the sun-exposed pots compared to shaded plants. These experiments showed that temperatures of 40C or higher, which commonly occur in container-grown plants exposed to solar radiation, can predispose chrysanthemum roots to severe Phytophthora infection.

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Harry K. Tayama and Stephen A. Carver

Residual activity of a single uniconazole spray (15 mg a.i./liter), uniconazole drench (600 μg a.i./pot), and daminozide spray (5000 mg a.i./liter) were compared to an untreated control using the `Bright Golden Anne' chrysanthemum [Dendranthema grandiflorum (Ramat.) Kitamura]. Based on weekly internode growth, spray and drench treatments with daminozide and uniconazole remained active for 2 to 2.5 and 3 to 3.5 weeks, respectively. Chemical names used: butanedioic acid mono (2,2-dimethylhydrazide) (daminozide); (E)-1-(p-chlorophenyl)-4,4-diemethyl 1-2(1,2,4-triazol-2-yl)-l-penten-3-01 (uniconazole).

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D.H. Willits, P.V. Nelson, M.M. Peet, M.A. Depa, and J.S. Kuehny

The results of six experiments conducted over 3 years were analyzed to develop a relationship between nutrient uptake rate and growth rate in hydroponically grown Dendranthema ×grandiflorum (Ramat.) Kitamura, cv. Fiesta. Plants subjected to two levels of CO, and three levels of irradiance in four greenhouses were periodically analyzed for growth and the internal concentration of 11 mineral elements. The resulting data were used to determine relative accumulation rate and relative growth rate, which were included in linear regression analyses to determine the dependence of uptake on growth. The regression equations were significant, with a slight trend toward nonlinearity in some elements. This nonlinearity seems to be related to the aging of the plant and suggests a process in the plant capable of controlling uptake rate, perhaps as a result of changes in the rate of formation of different types of tissues.