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  • Author or Editor: Yin-Tung Wang x
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This is the first report on how leaf harvest techniques and sulfur may affect leaf initiation and yield of Aloe barbadensis Miller (syn. Aloe vera L.). Two long-term experiments were conducted to determine the effects of supplemental mineral nutrients, severity of harvest, and sulfur application on leaf yield of this species. Plants were each grown in a 38-L pot with or without monthly applications of a 20N–8.6P–16.6K water-soluble fertilizer. In the first experiment, beginning in June 1994 (7 months after initiation), the lower leaves were harvested every 3 months with 12, 15, or 18 leaves remaining per plant. All plants were harvested to 12 leaves at the final harvest in Mar. 1997. Fertilized plants that were harvested to 12 leaves produced 81 leaves each during the 3-year period, whereas those harvested to 15 or 18 leaves each produced 76 leaves. In contrast, each of the nonfertilized plants produced 36 leaves. Fertilization tripled the cumulative weight of harvested leaves over a 3-year period. The initial quarterly and cumulative leaf weights were higher in plants harvested to 12 leaves than those harvested to 15 or 18 leaves. However, this difference diminished and disappeared over time. Fertilized plants harvested to 18 or 15 leaves yielded over 10.8 kg annually, whereas nonfertilized plants with 12 leaves produced an average of 3.5 kg leaves per plant. In the second experiment (with or without fertilizer and micronutrient and 0, 25, 50, or 100 g/pot of powdered sulfur per year), plants responded similarly to fertilization as they did in the first experiment. The added micronutrients (25 g/pot per year) had no effect on plant growth. The highest rate of sulfur resulted in few leaves being harvested and reduced cumulative leaf weight in fertilized plants, but did not affect the number of harvestable leaves or their total weight in nonfertilized plants. Soil pH declined from 7.6 to 4.6 as a result of fertilization regardless of the amount of sulfur being applied. In both experiments, plants that received fertilizer had slight cold injury on the abaxial side of some south-facing leaves. The results suggest the importance of fertilizer application to enhance leaf initiation rate. Plants should be harvested to leave no fewer than 15 leaves, preferably 18, on the plant to maintain high leaf yield.

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It was unknown how prolonged periods of cool days and warm nights affect Phalaenopsis Blume hybrids, which perform crassulacean acid metabolism and absorb CO2 primarily at night. The ‘Lava Glow’ plants vegetatively propagated from a hybrid Doritaenopsis (Phalaenopsis Buddha's Treasure × Doritis pulcherrima Lindley*), 15 cm in leaf span, were grown at day/night (12 hours each daily) temperatures of 30/25, 25/30, 25/20, or 20/25 °C under 170 μmol·m−2·s−1 PPF. After 37 weeks, plants at the higher average daily temperature of 27.5 °C (ADT, 30/25 and 25/30 °C) produced more leaves than the lower 22.5 °C ADT. Those grown at 30/25 °C had the largest leaf span and combined length of the new leaves. Plants at 30/25, 25/30, 25/20, or 20/25 °C had 5.0, 4.7, 3.6, and 2.8 new leaves that were 72, 61, 44, and 29 cm in total length, respectively. Warmer nights than days resulted in a small leaf span, reduced leaf growth, and shorter leaves that were particularly noticeable at the 22.5 °C compared with 27.5 °C ADT. Leaves that emerged and grew at the lower ADT had a reduced length to width ratio and a more oval shape. The most striking effect of the 20/25 °C treatment was that 14 of 15 plants bloomed, whereas only five plants at 25/20 °C and none at 30/25 or 25/30 °C produced flowers. Similar results were obtained in a second experiment using 30/20, 20/30, 25/15, or 15/25 °C. After 29 weeks, all plants at 15/25 °C bloomed, whereas none in the other treatments had flowers. Long-term exposure to 15/25 °C resulted in slow leaf production and undesirable small leaves. These results suggest that day and night temperature may both affect growth and flowering of this orchid.

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Bougainvillea cuttings propagated in fall and winter often bloom profusely before putting out adequate shoot growth. These large flowers shade the small leaves, resulting in slow growth. In an attempt to solve this problem, rooted `Juanita Hatten' cuttings were planted in 11.5-cm pots, clipped to 5 cm, and placed under natural short day or a 4-hour night interruption on 7 Dec. Plants were sprayed on 8 Dec. and again on 2 Jan. with 0, 50, 100, or 200 mg GA3/L or a combination of GA3 and PBA at 200 mg·L–1. Data were taken on the uppermost new shoot of each plant. Under long-day conditions, the first inflorescence was produced on the first node of all control plants, whereas plants treated with GA3 at 100 or 200 mg·L–1 produced the first inflorescences on higher nodes. The number of inflorescences on this shoot was unaffected by any treatment. GA3 treatment resulted in longer shoots (6.7–10.2 cm vs. 2.4 cm) and more leaves (13.4–l6.2 vs. 7.5), with greater effects at higher concentrations. These shoots had several inflorescences at the base, followed by many nonflowering nodes and additional flowers near the tip. The GA3 + PBA treatment had no effect on the position of the first inflorescence. However, shoots had twice as many nodes and fewer inflorescences than the controls and were shorter than those treated with GA3 alone. Plants under short day responded similarly to respective treatments under the long-day conditions. Tests will be conducted to determine if stock plants need to be treated in early fall and cuttings collected from the new growth to prevent early flowering.

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Lilium longiflorum Thunb. `Nellie White' plants were selected when their first flower buds reached 2 or 5 cm in length, sprayed with 2 mL of PBA at 0 or 500 mg·L–1, and then placed under 1440 or 60 μmol·m–2·s–1 photosynthetic photon flux (PPF) during flowering. PBA resulted in delayed anthesis and increased dry matter accumulation in flowers under the high PPF but had no effect under the low PPF. PBA did not decrease the severity of flower bud abortion under the low PPF. Application of PBA induced the formation of numerous bulbils in the leaf axils. Regardless of PPF, PBA-treated plants had less dry weight in the main bulbs than the control plants. Chemical name used: N-(phenylmethyl)-9-(tetra-hydro-2H-pyran-2-yl)-9H-purin-6-amine (PBA).

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On 6 Sept. 1996, container-grown vegetatively propagated Phalaenopsis Atien Kaala `TSC22' plants were harvested and individually weighed. The bare-root plants were packed in cartons with shredded newspaper and placed in incubators at 15, 20, 25, or 30°C air temperature. Control plants were undisturbed. After 4, 7, or 14 days, one-third of the plants were removed from each temperature treatment, weighed, planted in pots, and then placed in a greenhouse. Mass loss (primarily water) increased with increasing air temperature and duration in storage. Symptoms of chilling injury (yellow blotches on leaves) were inversely related to 15 and 20°C storage temperatures. Chilling injury became more severe as storage duration increased. Plants had little or no chilling injury at 25 and 30°C, regardless of storage duration. Leaf loss was most severe on plants stored at 15°C for 7 or 14 days or at 30°C for 14 days. Increased storage duration up to 14 days did not affect the time of spiking (appearance of the flowering shoot) for plants stored between 15 and 25°C. Those kept at 30°C, regardless of the duration, spiked 5 to 8 days after the control. The results suggest that vegetative Phalaenopsis plants harvested in late summer should be stored and shipped at 25°C. Under such conditions, plants could lose 20% of the fresh mass between harvesting and planting without adversely affecting subsequent performance.

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Leaf blades, axillary buds, shoot tips, green bark, suberized bark, or the whole plant of container-grown Hibiscus rosa-sinensis L. cv. Jane Cowl were treated with uniconazole. Applying uniconazole (50 mg·liter-1) to axillary buds or the green bark below a bud immediately after pruning limited elongation of the first three internodes. Length of the fourth internode was unaffected, regardless of the site of uniconazole application. When used on plants with 24-day-old shoots, uniconazole (40 mg·liter -1) applied to the whole plant provided the only satisfactory height control. Leaf size was reduced by nearly 50%, with a concomitant increase (12%) in fresh weight per unit area. GA3 (50 mg·liter-1, was more effective in promoting elongation of shoots previously retarded with a drench application of uniconazole (0.1 mg/2.6-liter pot) when applied to the whole shoot, leaf blades, or shoot tip. Application of GA, only to the stein surface, whether old or young, did not effectively encourage the growth of shoots of plants previously treated with uniconazole. Chemical names used: (E)-1-(p-chlorophenyl) -4,4-dimethyl-2-(1,2,4-triazole-1-yl)-1-penton-3-ol (uniconazole); analogue of (1α,2β,4 α,4bβ,10β)-2,4a,7-trihydroxy-1-methyl-8-methylenegibb-3-ene-1,10 dicarboxylic acid 1,4a-lactone (GA3).

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An experiment was initiated to determine the effect of a low N, high P and K fertilizer applied during the flowering season on a hybrid moth orchid (Phalaenopsis TAM Butterfly Blume.). On 1 Sept., plants of flowering size receiving N, P, and K at 100, 44, and 83 mg·L–1, respectively, from a 20N–8.8P–16.6K soluble fertilizer were given N, P, and K, at 30, 398, and 506 mg·L–1 (high P), respectively, at each or every fourth irrigation. Control plants continued to receive the 20N–8.8P–16.6K fertilizer. The high P treatments, regardless of the frequency of application, had no effect on the date of emergence of the flowering stem (spiking), anthesis, or flower size. All plants treated with the high P fertilizer had fewer flowers (15 to 19) than the controls (24 flowers). Continuous application of adequate N appears to be more important than low N and increased P for optimal flowering. In a separate experiment using the same hybrid orchid, terminating fertilization completely on 1 Sept., 29 Sept., or 27 Oct. or when the flowering stems were emerging (1 Oct.) reduced flower count (≤19 vs. 24). Flower longevity was reduced by 12 d when fertilization was terminated on 1 Sept. Flower size was unaffected by any treatment in either experiment. Discontinuing fertilization prior to late November reduced flower count. Withholding fertilization for extended periods resulted in red leaves, loss of the lower leaves, and limited production of new leaves.

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Seedling Phalaenopsis (P. Taisuco Eagle × P. Taisuco Rose) plants with an 8- to 10-cm leaf span were grown in 10-cm pots filled with a medium consisting of 70% fine fir bark and 30% peatmoss (by volume). Plants were given (in N–P2O5–K2O) 10–30–20, 15–10–30, 15–20–25, 20–5–19, 20–10–20, or 20–20–20 fertilizers at the 100 or 200 mg N/liter rate. Pots were leached with water following every two fertigations. After 7 months, leaf span, leaf size, total leaf area, and fresh weight were not affected by fertilizer type. The differences in leaf numbers were small. The higher rate of fertilizer resulted in plants with wider leaf span (32.8 vs. 28.5 cm), more (5.5 vs. 4.8), larger (103 vs. 89 cm2) leaves, and greater total leaf area (355 vs. 275 cm2) than did the lower rate. In another experiment, similar plants with a leaf span of 15 to 18 cm were grown in 10-cm pots with 100% fine fir bark or a mixture of 80% fine fir bark and 20% peatmoss. They were fertigated with water having an EC - 0.05, 0.40, 0.75, 1.10, or 1.40 dS·m–1 containing 1 g·liter–1 20–20–20 fertilizer three times and then drenched with their respective water containing 0.6 g·liter–1 Ca NO3)2·4H2O. After 11 months, water salinity did not affect the date of spiking. Plants receiving water with EC = 1.10 dS·m–1 had more leaves and spikes than other treatments. Plants in the bark/peatmoss mix began spiking earlier, had more leaves (6.7 vs. 5.7), and more inflorescences (1.9 vs. 1.5) than those in 100% bark. There was no salinity x medium interaction in all the parameters recorded.

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Potted mature Phalaenopsis `Joseph Hampton' orchid (clone Diane) plants were placed in each of four growth chambers with 0, 8, 60, or 160 μmol·m–2·s–1 photosynthetic photon flux (PPF) for 12 hours daily and at 20C day/15C night air. Plants under 160 or 60 μmol·m–2·s–1 PPF began spiking (an elongating reproductive bud protruding through the base of its subtending leaf) in an average of 28 or 34 days, respectively. None of the plants placed under 0 or 8 μmol·m–2·s–1 PPF started spiking within 6 weeks. These plants, following return to a greenhouse, spiked and flowered 8 weeks later than those receiving 160 μmol·m–2·s–1. In a second experiment, plants were placed in each of three growth chambers and kept in complete darkness at 20C day/15C night for 2, 4, or 6 weeks before exposure to 160 μmol·m–2·s–1 PPF. Air was maintained at 20C day/15C night for an additional 6 weeks and then raised to 25C day/20C night to accelerate flowering. Plants exposed to 2, 4, or 6 weeks of darkness required 45, 60, or 77 days, respectively, to reach spiking. However, all plants spiked at similar times (31 to 35 days) after lighting began. Anthesis occurred at progressively later dates for plants placed in darkness for increasing durations, but plants in all treatments required 123 days to reach anthesis following their exposure to light. Flower count and size were not affected in both experiments.

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Blooming Phalaenopsis orchids have become a popular pot plant in recent years. Plants start producing spikes after experiencing cool air in early fall, bloom in early spring, and become limited in supply after April when market demand is strong. Deferring spiking and flowering by maintaining the greenhouse air constantly above 28°C is cost prohibitive. Previous research has discovered that plants must be given light while being exposed to cool air to induce spiking. In Fall 1994, 2-year old Phalaenopsis TAM Butterfly plants were exposed to repeated cycles of 1 day in darkness and another day in light (1D/1L), 4D/3L, 7D/7L, or 0D/7L (continuous lighted control) between 15 Sept. and 16 Dec. Each plant was removed from the treatment once it had started spiking. The control plants bloomed on 20 Jan. 1995, whereas the 4D/3L plants did not reach anthesis until April 17, nearly three months later. Flowering of the 1D/1L and 7D/7L plants was also deferred until early April. The treatments had no adverse effect on flower count or size. In 1995, 3-year old plants were exposed to 0D/7L (control), 2D/5L, 3D/4L, 4D/3L, or 5D/2L from 15 Sept. to 22 Jan. 1996. The control plants spiked on 17 Oct. and bloomed on 8 Feb. 1996 when spikes had just emerged from plants in the 5D/2L treatment. The 5D/2L plants are expected to bloom in late May or early June. The other treatments were not as effective as that in 1994 and resulted in blooming only 2–3 weeks after the untreated control. The results of this research will help producers to stagger or precisely program the time of flowering to meet the market demand.

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