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  • Author or Editor: Arthur C. Cameron x
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Many polycarpic herbaceous perennials are known to have a cold-requirement for flowering. To determine the range and relative effectiveness of vernalization temperatures for flower induction, clonally propagated plants of veronica (Veronica spicata L.) ‘Red Fox’ and laurentia [Laurentia axillaris (Lindl.) E. Wimm.] were exposed to temperatures from −2.5 to 20 °C at 2.5 °C increments for 0, 2, 4, 6, or 8 weeks (veronica ‘Red Fox’) and 0, 2.5, 5, 7.5, 10, 12.5, or 15 weeks (laurentia). After treatments, growth and flowering were monitored in a glass greenhouse set at 20 °C with an average daily light integral of ≈5 mol·m−2·d−1. Both veronica ‘Red Fox’ and laurentia exhibited obligate vernalization requirements for flowering, but the temperature–response curves were distinctly different. A minimum of 4 weeks at −2.5 and 0 °C, 6 weeks at 2.5 °C, and 8 weeks at 5 and 7.5 °C was required for complete (100%) flowering of veronica ‘Red Fox’, while a minimum of 5 weeks at 5 to 10 °C, 7.5 weeks at 12.5 °C, and 10 weeks at 2.5 °C were required for complete flowering of laurentia. For veronica ‘Red Fox’, node number under each flower and flower timing were relatively fixed following up to 8 weeks at each temperature, although these values generally decreased at each temperature with extended exposure for laurentia. Based on percent flowering and percentage of lateral nodes flowering, vernalization of veronica ‘Red Fox’ was most effective at 0 and −2.5 °C, while based on percent flowering and flower number, vernalization of laurentia was most effective at 5 to 10 °C.

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Abstract

After 4 days, zygocactus plants (Schlumbergera truncata) exposed to air containing 0.5, 5 and 50 µl/liter C2H4 or held in the dark at 26°C dropped all their buds and flowers. Foliar application of silver thiosulfate (STS) significantly reduced flower and bud abscission of zygocactus plants stressed by exposure to C2H4 or 26°C plus dark even 4 weeks after application. Phytotoxicity was negligible when the silver concentration was 2 mm or less.

Open Access

In one set of modified-atmosphere (MA) packages of cut broccoli (Brassica oleracea L., Italica Group), O2 partial pressures ranged from 1.2 to 3.6 kPa at 0C [88 packages, 0.00268-cm-thick low-density polyethylene (LDPE) film, 600-cm2 film area, 40±0.5 g cut broccoli], and in another set (94 packages, same film and area as before, 25±0.5 g cut broccoli) they ranged from 5.0 to 9.2 kPa. For characterizing O2 uptake as a function of O2 partial pressure and determining anaerobic fermentation induction point at 0C, a range of steady-state package O2 partial pressures was generated by placing different amounts of cut broccoli (10 to 160 g) in LDPE packages. Oxygen uptake was modeled using a Michaelis-Menten-type equation. The maximum rate of product O2 uptake when O2 partial pressure was nonlimiting and the package O2 partial pressure corresponding to half-maximum O2 uptake were estimated as 147±3 nmol·kg-1·s-1 and 0.26±0.025 kPa, respectively. Respiratory quotient and head space ethanol increased sharply below package O2 partial pressures of 0.15 kPa, indicating stimulation of fermentation within the packages. The frequency distributions of CO2 production rates were measured for 80 samples of 100 g each of cut broccoli at two O2 partial pressures (21.0 kPa and 1.3 kPa) using a flow-through method. The average coefficient of variation of the CO2 production rate was ≈5%. Frequency distributions of O2 partial pressures were modeled as a function of product-to-product variation in O2 uptake and package-to-package variation in film permeability using the estimated O2 uptake characteristics and coefficient of variation. The model was used to predict the target O2 partial pressures for the design of cut broccoli MA packages. It was predicted that the packages for cut broccoli at 0C should be designed for a target O2 partial pressure of 2.54 kPa to have actual package O2 partial pressures ≥1.0 kPa at 0.0001% probability level. Film specifications for MA packaging of cut broccoli at 0C were calculated based on the predicted target O2 partial pressures.

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The growth and development of Achillea ×millefolium L. `Red Velvet', Gaura lindheimeri Engelm. & Gray `Siskiyou Pink' and Lavandula angustifolia Mill. `Hidcote Blue' were evaluated under average daily light integrals (DLIs) of 5 to 20 mol·m-2·d-1. Plants were grown in a 22 ± 2 °C glass greenhouse with a 16-h photoperiod under four light environments: 50% shading of ambient light plus PPF of 100 μmol·m-2·s-1 (L1); ambient light plus PPF of 20 μmol·m-2·s-1 (L2); ambient light plus PPF of 100 μmol·m-2·s-1 (L3); and ambient light plus PPF of 150 μmol·m-2·s-1 (L4). Between 5 to 20 mol·m-2·d-1, DLI did not limit flowering and had little effect on timing in these studies. Hence, the minimum DLI required for flowering of Achillea, Gaura and Lavandula must be <5 mol·m-2·d-1, the lowest light level tested. However, all species exhibited prostrate growth with weakened stems when grown at a DLI of about 10 mol·m-2·d-1. Visual quality and shoot dry mass of Achillea, Gaura and Lavandula linearly increased as DLI increased from 5 to 20 mol·m-2·d-1 and there was no evidence that these responses to light were beginning to decline. While 10 mol·m-2·d-1 has been suggested as an adequate DLI, these results suggest that 15 to 20 mol·m-2·d-1 should be considered a minimum for production of these herbaceous perennials when grown at about 22 °C.

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Flowering of Aquilegia is generally considered to require vernalization, while photoperiod has little or no effect. The cold treatment is most effective when plants have passed the juvenile stage (often 12 to 15 leaves) prior to vernalization. We performed experiments on a cultivar reported to have a reduced vernalization requirement. Seedlings of Aquilegia ×hybrida Sims `Origami Blue and White' in 128-cell plug trays with four or five leaves were either placed directly into a 5 °C cooler or transplanted to 13-cm containers. Plants were grown (bulked) for 0, 3, or 6 weeks at 20 °C under 9-h short days (SD) or 16-h long days (LD) provided by incandescent lamps at 1 to 3 μmol·m-2·s-1. Plants had seven or eight leaves after 3 weeks bulking and 13 or 14 leaves after 6 weeks bulking. They were then cooled at 5 °C for 0, 5, or 10 weeks and placed in a common forcing environment of 20 °C under an LD provided by high-pressure sodium lamps. Aquilegia plants placed directly into the forcing environment flowered in 89 and 97 days in years 1 and 2, respectively. Flowering percentage of plants cooled in the plug tray decreased with increasing duration of cold treatment, and only 15% flowered after a 10-week cold treatment. All plants bulked for 3 or 6 weeks prior to cold treatment flowered, and in 26 to 35 days. Surprisingly, all plants that were moved directly from bulking treatments to the forcing environment (no cold treatment) flowered, and flowering was most rapid (36 days) in plants exposed to 6 weeks of SD before forcing. Therefore, our data indicate that SD can at least partially substitute for a cold treatment in this Aquilegia cultivar.

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Natural variation of product respiration rate and temperature variation during shipping and marketing influence the atmosphere inside MA packages. Respiration rate variation data was collected at 0C and 5.5C for `Allstar' and `Honeoye' strawberries and at 5.5C for `Heritage' raspberries. Coefficient of variation was 8% for raspberries and ranged from 6.5% to 12.5% for strawberries. To determine package-to-package variations, steady-state O2 partial pressures were measured in 100 similarly designed packages and frequency distributions were constructed. For `Honeoye' variety, `O2 partial pressures ranged from 3.5 kPa to 13.7 kPa with a median of 7.5 kPa in one set of packages and from 0.4 to 1.65 kPa with a median of 0.6 kPa in another set of packages with different design. Large variations were also observed for `Allstar' variety and raspberries. The results compared well with package O2 distributions predicted by a mathematical model that was constructed based on respiration rate variation. A modeling approach was used to predict frequency distributions and changes in gas levels in strawberry and raspberry packages for several possible temperature variation situations and for different types of package designs.

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We performed experiments to determine the photoperiodic response of Ceratostigma plumbaginoides Bunge., or leadwort, which is a low-growing hardy herbaceous perennial native to China with deep gentian-blue flowers. Tip cuttings were rooted in 72-cell trays and grown under a 24-hour photoperiod for 2 weeks and then transplanted into 11.4-cm pots and grown for one more week. Plants were then placed under different primary photoperiods (10, 16, or 24 hours) for 4, 6, or 8 weeks, then transferred to secondary photoperiods (10, 14, 16, or 24 hours) at a constant 20 °C. Pots were also placed under continuous 10, 14, 16, or 24 hours. Nearly all plants flowered under all treatments except under continuous 10- or 24-hour photoperiods, in which no plants flowered. Plants grown under 14 hours flowered earliest (50 days), followed by plants under the 16-hour primary treatment. The 10-hour primary treatment delayed flowering for as long as its duration, whereas the 16-hour primary photoperiod initiated rapid flowering, regardless of duration and subsequent secondary photoperiod. Flowering was also delayed when the primary photoperiod was 24 hours. Collectively, these responses indicate that Ceratostigma is an intermediate-day plant.

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Two experiments were conducted to quantify the effect of vernalization temperature and duration on flowering of Dianthusgratianopolitanus `Bath's Pink'. In Expt. 1, plants were vernalized at 5 °C for 0, 3, 6, 9, 12, or 15 weeks and in Expt. 2, plants were vernalized at 0, 5 or 10 °C for 0, 2, 4, 6 or 8 weeks. After treatments, plants were forced in a greenhouse at 20 °C. Node development, days to first visible bud (DVB), days to first open flower (DFLW), number of buds and height at FLW were recorded. In Expt. 1, 10% of nonvernalized plants flowered and 100% of vernalized plants flowered. As vernalization duration increased from 3 to 15 weeks, DTVB decreased from 24 to 13. Average DFLW were 114, 41, 34, 33, 33, and 28 for 0-, 3-, 6-, 9-, 12-, and 15-week treatments, respectively. In Expt. 2, 40% of plants flowered without vernalization. Following 2 weeks of vernalization at 0 °C, 80% of plants flowered and as the duration of vernalization increased to ≥4 weeks, all plants flowered. Average DFLW decreased from 38 to 28 following 2 or 4 weeks of vernalization at 0 °C. Longer vernalization did not further reduce DFLW. All plants cooled at 5 °C flowered and vernalization duration did not affect DFLW. Percent flowering after vernalization at 10 °C for 2, 4, 6, and 8 weeks was 20%, 60%, 90%, and 100%, respectively, and average DFLW were 46, 45, 35, and 33, respectively. In conclusion, vernalization is required to force D.`Bath's Pink'. To achieve complete flowering, plants should be vernalized at 5 °C for ≥2 weeks or at 0 °C for 4 weeks or at 10 °C for 8 weeks. Qualitative effects of vernalization such as node development and number of buds and height at FLW will be discussed.

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The influence of cold treatments and photoperiod on flowering of 8- to 11-node and 18- to 23-node Lavandula angustifolia Mill. `Munstead' plants from 128-cell (10-mL cell volume; P1) and 50-cell (85-mL cell volume; P2) trays, respectively, was determined. Plants were stored at 5 °C for 0, 5, 10, or 15 weeks, then forced under a 9-h photoperiod (SD), or under a 4-h night-interruption (NI) (2200 to 0200 hr) photoperiod at 20 °C. Percentage of plants flowering, time to flower, and plant appearance were evaluated. Increasing duration of cold treatment was associated with an increase in flowering percentage in plants from both cell sizes. More plants flowered under NI than SD except in P2 cooled for 15 weeks, where all plants flowered. Average time to visible bud (VB) and to opening of the first flower (FLW) generally decreased with increasing duration of cold treatment. Inflorescence count in P2 plants increased with increasing duration of cold treatment. To determine the relationship between forcing temperature and time to flower in L. angustifolia `Munstead', three sizes of plants were exposed to 5 °C for 13 weeks and then forced under a 4-h NI (2200 to 0200 hr) at 15, 18, 21, 24, or 27 °C. Plants generally flowered more quickly at higher temperatures, time to FLW decreasing from 77, 71, and 60 days at ≈15.6 °C to 46, 40, and 36 days at ≈26 °C for P1, P2, and 5.5-cm (190-mL pot volume) (P3) plants, respectively. Generally, P1 plants flowered 5 to 10 days later than P2, and P2 flowered 5 to 10 days later than P3.

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