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  • Author or Editor: Theo Blom x
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The effect of constant 16C and noncontrolled soil temperature on flowering of four Alstroemeria cultivars grown in a greenhouse was studied over 3 years. Soil temperature regime did not influence either the start or cessation of flowering. During spring/summer, production was 15% lower under constant soil temperature, irrespective of cultivar. During fall/winter, the effect of constant soil temperature was cultivar-dependent; yield of `Red Sunset' was increased by 150%, while that for `Rio' decreased by 2270 relative to the noncontrolled. Annual production was not affected, but the ratio between the production of spring/summer and fail/winter decreased from 3.1 to 2.2 for noncontrolled and constant soil temperature, respectively.

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On 15 Sept., 15 Oct., 15 Nov., and 15 Dec., summer-rooted cuttings of Euonymus fortunei (Turcz.) Hand.-Mazz. `Emerald Gaiety' from both outdoor (natural cold exposure) and greenhouse (no natural cold exposure) locations were transferred to ambient, 16-h incandescent or a 16-h high-pressure sodium (HPS) lighting treatment in a greenhouse 10C). Regardless of lighting treatment, cuttings transferred from outdoors in December had the most shoot growth, followed by cuttings transferred in November. None of the lighting treatments induced a resumption of growth at any transfer date. After 15 days of storage at 1C, outdoor and/or greenhouse-grown cuttings that previously had not received any or partial amounts of natural cold exposure broke dormancy under ail lighting treatments and grew to similar heights as those of the December transfer date. Storage at 1C for 30 days inhibited growth compared to storage for 15 days. The degree of inhibition was greatest for plants exposed to HPS lighting.

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The objectives of the study were to determine whether raspberries responded to decreased red to far-red ratio and whether it was more effective at the beginning or end of the dark period. Increased proportions of far-red light increased the internode length when at the beginning of the dark period on the three raspberry cultivars `Lauren',`Reveille', and `Titan'. Cultivars varied in that internode length also increased in ambient daylength compared to short days in `Lauren' and `Reveille', but not in `Titan'. They also responded differently to photoperiod: `Titan' and `Lauren' grew under short days, whereas `Reveille' ceased growth.

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Potted bulbs of Lilium longiflorum Thunb. `Ace', `Nellie White', and `Snow White' were grown under either ambient photo period (APP), 8-h photo period using blackout (no twilight) between 1600 and 0800 HR (8PP) or 8PP extended with 1-h of low-intensity far-red radiation (9PP) at end-of-light period in a greenhouse with either a +5 °C DIF or a –5 °C DIF (= day – night temperature). In a second experiment, Easter lilies were also grown under APP, 8PP, and 9PP regimes with a constant day/night temperature (0 °C DIF) but with either a +5 °C or –5 °C temperature pulse for 3-h during end-of-light period. Each experiment was replicated twice and data was averaged over 2 years. The +5 °C DIF regime produced plants which were 19% taller than under –5 °C DIF. Plants grown under APP were 32% and 25% taller than under 8PP in the +5 °C and –5 °C DIF regimes, respectively. Regardless of the DIF regime, plant height under the 9PP was the same. In the second experiment, there was no significant difference in plant height of plants grown with the –5 °C compared with the +5 °C pulse at end-of-light period.

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Summer-grown Hydrangea macrophylla subsp. macrophylla var. macrophylla (Thunb.) were exposed for 1 week to CzH4 at 0,0.5,2.0,5.0,50, or 500 μl·liter-1 in dark storage at 16C for defoliation before cold storage. The number of leaves remaining per shoot for all cultivars decreased with C2H4 concentration, and >5 μl C2H4/liter was effective in defoliating `Kasteln', `Mathilda Gutges', and `Todi' but not `Merritt's Supreme'.

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Four freesia cultivars were exposed to 24 hour·day-1 high-pressure sodium (HPS) lighting during various stages of their development. Upon emergence, freesia plants were exposed to the following four lighting treatments: 1) ambient; 2) ambient until shoot length was 5 to 8 cm followed by HPS lighting until flowering; 3) HPS lighting until shoot length was 5 to 8 cm followed by ambient lighting; and 4) continuous HPS lighting. Supplemental HPS lighting was provided at 37 μmol·m-2·s-1 at plant level in a glasshouse. Continuous lighting or lighting during flower development hastened flowering but reduced the number of flowering stems per corm, as well as stem length and weight. Lighting during the vegetative and flower initiation periods produced minor effects. The main benefit of supplemental lighting was found in total corm weight.

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The Al content was determined in roots, buds, and stems of dormant florists' hydrangeas [Hydrangea macrophylla subsp. macrophylla var. macrophylla (Thunb.) `Mathilda Gutges' and `Brestenburg'] that were or were not treated in the field with aluminum sulfate. During the greenhouse forcing stage, previously nontreated plants were subjected to four successive weekly subirrigated applications of aluminum sulfate totalling 4, 8, 12, or 16 g/pot. Applications were early (weeks 2, 3, 4, 5) or late (weeks 6, 7, 8, 9), using the start of forcing as week = 0. The Al contents in stems and buds of dormant plants were about five to six times higher in field-treated than in nontreated plants. Roots were the primary location of Al accumulation (≈70%). Aluminum sulfate applications of 12 to 16 g/pot during greenhouse forcing provided commercially acceptable blue plants. Maximum foliar Al concentration was 50% higher in early than in late-treated plants and calculated to occur with 14.5 and 12.2 g aluminum sulfate/pot for early and late-treated plants, respectively. There was a positive correlation (r = 0.74) between blueness ranking and the Al foliar concentration of the two uppermost expanded leaves taken from flowering plants.

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Low volume drip (2 l/h) was compared with 2 subirrigation ('trough' and `ebb and flo') systems for production of poinsettias and chrysanthemums in 15 cm diameter (1.6 l) `azalea' pots. Irrigation frequency as well as fertilizer rates were the same for all systems. The drip system received 280 ml per watering.

Two plantings of poinsettias (fall) as well as two plantings of chrysanthemums (spring and summer) showed no differences in plant growth between the drip and the subirrigation systems. Water uptake by the medium was similar for all irrigation systems, but water and fertilizer application was 70% higher for the drip system. Nutrients, measured at 4 depths within the pot at monthly intervals, increased with time and was markedly more concentrated in the top layer, regardless of the irrigation system.

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Potted greenhouse-forced `Nellie White' Easter lilies (Lilium longiflorum Thunb.) were irrigated from emergence with water at 2, 5, 8, 11, or 15 °C either onto the shoot apex (overhead) or onto the substrate for a 0, 2-, 4-, 6-, 8-, 10-, or 12-week period. Control treatment was at 18 °C, either overhead or on substrate. When irrigation water was applied overhead for the entire period between emergence and flowering (12 weeks), plant height increased linearly with the temperature of irrigation water (1.75 cm/°C). As the period of application with cold water increased from 0 to 12 weeks, plant height decreased both in a linear and a quadratic manner. Forcing time was negatively correlated with height with the shortest plants delayed by 3 to 6 days. Water temperature did not affect bud abortion or the number of yellow leaves. Irrigation water temperature had no effect on plant parameters when applied directly on the substrate.

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Chrysanthemum morifolium Ramat. cv. `Yellow Favor' was grown single stem in 10cm pots on an ebb and flow benching system. A 2×2 factorial design was employed with 2 sources of N (100 NO3 and 50 NO3 :50 NH4 +), delivered at 18 mM, and 2 quantities of N supplied, (200 mg and 400 mg), with 200 mg supplied by wk 3 and 400 mg supplied by wk 5. Plants were harvested at two wk intervals, separated into leaves, stems plus petioles and inflorescence (when developed) and analyzed for total and NO3 - N, with reduced N being estimated as the difference between these two values. Plant tissue (leaves and stems plus petioles) NO3 - levels showed similar trends for the 200 and 400 mg N supply, with a maximum at the 4th to 6th wk. At flowering, (wk 10) significant tissue NO3 - levels were found only in plants supplied 400 mg of N. Plants supplied with 50:50 NH4 +: NO3 - initially had significantly greater reduced N and leaf area than NO3 - supplied plants, although differences diminished towards flowering. During floral development (wk 8 to 10), at which time no additional N was accumulated by the plant, significant amounts of reduced N was remobilized from the stem plus petioles and leaves to the developing inflorescence.

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