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  • Author or Editor: A. C. Cameron x
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Bare-root garden rose' (Rosa) cultivars Show Biz, Tropicana, Hotel Hershey, and Femme were packaged according to standard nursery practice with roots surrounded by peat. After 4 weeks of simulated marketing at 23C, the plants produced half as many breaks, half as many flowers, half as much seasonal cane growth, and had reduced survival when field-grown for 1 year, compared to plants held 4 weeks at 3C. Waxing of canes before treatment reduced water loss during simulated marketing and increased lateral breaks, total season cane growth, and, in some cases, flower production. Waxing also induced faster development of new lateral breaks, but, at 23C, induction occurred before planting and these breaks survived poorly in the field. The antitranspirant Cloud Cover did not affect moisture loss or improve field performance.

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Many herbaceous perennials require vernalization although effective temperatures (ET) and durations for specific species are largely unknown. To investigate vernalization of Laurentia axillaris (Lindl.) E. Wimm. and Veronica spicata L. `Red Fox', vegetative plugs were stored at -2.5, 0.0, 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 °C for 0 to 15 weeks (Laurentia) or 0 to 8 weeks (Veronica). Following storage, plugs were grown in a 20 °C glass greenhouse with a 16-h photoperiod. Laurentia plugs did not survive storage at -2.5 or 0 °C. Survival varied for plants stored at 2.5 °C, and some plants flowered. ET and the minimum duration for 100% flowering of Laurentia were: 5 weeks at 5 to 10 °C and 10 weeks at 12.5 °C. Time to first visible bud and node number below first visible bud decreased with increasing duration at ET. Veronica plugs survived storage at all temperatures. 100% flowering occurred when plants were vernalized at -2.5 and 0 °C for 4 or more weeks, at 2.5 and 5.0 °C for 6 or more weeks, and at 7.5 °C for 8 weeks. Incomplete vernalization (19 to 93%) occurred at temperatures of 2.5 °C for 4 weeks, 5 °C for 4 or 6 weeks, 7.5 °C for 6 weeks and at 10 °C for 6 or 8 weeks. Vernalization did not occur above 10 °C or following 2 weeks storage at any temperature. The percentage of reproductive lateral shoots increased while node number below the inflorescence remained constant or decreased with increasing storage at ET. The results indicate distinct vernalization optima for the two species; Laurentia 5 to 10 °C, and Veronica -2.5 to 0 °C. These differences provide evidence that separate “thermometers” may be involved in vernalization perception.

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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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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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Calla (Zantedeschia Spreng.) growers were studied as members of an expanding sector in the New Zealand floricultural industry. The calla sector is characterized by diverse-size firms scattered throughout the two main islands of New Zealand. Growers differ in their skill and experience with calla production. Problems are both grower-specific (e.g., control of diseases, postharvest disorders) and sector-wide. Examples of the latter include the prioritizing and funding research, interacting with science organizations and planning sector marketing strategy. Both sets of problems have been exacerbated by the progressive withdrawal of research and extension support services traditionally provided by government agencies. There is competition between the floriculture industry and calla sector-based grower organizations. The leadership role of a strong grower organization, in this case the New Zealand Calla Council (NZCC), is seen as an essential forum for growers, and as the link between growers, exporter organizations, scientists and central government. Good communications between the industry organization and growers is essential to identify and prioritizeproblems and to transfer information to individual growers through workshops, newsletters and manuals. To maintain its effectiveness, the NZCC does not satisfy the needs of smaller growers at the expense of the larger, influential growers. Rather, it seeks to the benefit the latter by upgrading the skill level of the industry, and by undertaking tasks too large for any individual business.

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Oenothera fruticosa L.`Youngii-Lapsley' and Stokesia laevis L'Hér. `Klaus Jelitto' are two hardy herbaceous perennials with great potential as pot crops. The vernalization and photoperiod requirements were examined for each species. Plants were cooled for 0, 3, 6, 9, 12, or 15 weeks at 5 °C with a 9-h photoperiod. After cold treatment, plants were forced in greenhouses at 20 °C under a 16-h photoperiod using high-pressure sodium lamps. The photoperiod requirement was determined by forcing plants at 20 °C with and without a 15-week cold treatment at 5 °C under 10-, 12-, 13-, 14-, 16-, 24-h and 4-h night interruption using incandescent lamps. Plants of Oenothera fruticosa `Youngii-Lapsley' cooled for 0 weeks did not flower. All plants cooled for 3 weeks flowered and time to flower decreased from 53 to 43 days as duration of cold increased from 3 to 15 weeks. `Youngii-Lapsley' flowered under every photoperiod, but time to flower and number of flowers decreased from 54 to 40 days as photoperiod increased from 10 to 24 h. Percentage flowering of Stokesia laevis `Klaus Jelitto' increased from 50 to 100, and time to flower decreased from 112 to 74 days as duration of cold increased from 0 to 6 weeks. Without a cold treatment, plants of `Klaus Jelitto' flowered only under daylengths of 12, 13, and 14 h. After cold treatment, plants flowered under every photoperiod except 24 h, and time to flower decreased from 122 to 65 days as photoperiod increased from 10 to 16 h. Additional aspects of flowering and the effect of different forcing temperatures will be discussed.

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Influences of vernalization duration, photoperiod, forcing temperature, and plant growth regulators (PGRs) on growth and development of Oenothera fruticosa L. `Youngii-lapsley' (`Youngii-lapsley' sundrops) were determined. Young plants were vernalized at 5 °C for 0, 3, 6, 9, 12, or 15 weeks under a 9-hour photoperiod and subsequently forced in a 20 °C greenhouse under a 16-hour photoperiod. Only one plant in 2 years flowered without vernalization, while all plants flowered after receiving a vernalization treatment, regardless of its duration. Thus, O. fruticosa had a nearly obligate vernalization requirement. Time to visible bud and flower decreased by ≈1 week as vernalization duration increased from 3 to 15 weeks. All plants flowered under 10-, 12-, 13-, 14-, 16-, or 24-hour photoperiods or a 4-hour night interruption (NI) in a 20 °C greenhouse following 15-weeks vernalization at 5 °C. Time to flower decreased by ≈2 weeks, flower number decreased, and plant height increased as photoperiod increased from 10 to 16 hours. Days to flower, number of new nodes, and flower number under 24 hour and NI were similar to that of plants grown under a 16-hour photoperiod. In a separate study, plants were vernalized for 15 weeks and then forced under a 16-h photoperiod at 15.2, 18.2, 20.6, 23.8, 26.8, or 29.8 °C (average daily temperatures). Plants flowered 35 days faster at 29.8 °C but were 18 cm shorter than those grown at 15.2 °C. In addition, plants grown at 29.8 °C produced only one-sixth the number of flowers (with diameters that were 3.0 cm smaller) than plants grown at 15.2 °C. Days to visible bud and flowering were converted to rates, and base temperature (Tb) and thermal time to flowering (degree-days) were calculated as 4.4 °C and 606 °days, respectively. Effects of foliar applications of ancymidol (100 mg·L-1), chlormequat (1500 mg·L-1), paclobutrazol (30 mg·L-1), daminozide (5000 mg·L-1), and uniconazole (15 mg·L-1) were determined on plants vernalized for 19 weeks and then forced at 20 °C under a 16-h photoperiod. Three spray applications of uniconazole reduced plant height at first flower by 31% compared with that of nontreated controls. All other PGRs did not affect plant growth. Chemical names used: α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol); (2-chloroethyl) trimethylammonium chloride (chlormequat); butanedioic acid mono-(2,2-dimethyl hydrazide) (daminozide); (2R,3R+2S,3S)-1-(4-chlorophenyl-4,4-dimethyl-2-[1,2,4-triazol-1-yl]) (paclobutrazol); (E)-(S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pent-1-ene-3-ol (uniconazole).

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Ethylene production of tissues excised from root, stem, leaf, inflorescence, and fruit of 16 plant species greatly increased following the application of 1-aminocyclopropane-1 carboxylic acid (ACC), an intermediate in the conversion of methionine to ethylene. Treatment with 1 mM ACC invariably increased the rate of ethylene production 10 to 1000 times over controls, whereas methionine at the same concentration was ineffective. Treatment with 0.1 mM ACC consistently increased ethylene production in all of the tissues tested, although only a few tissues responded to 0.01 mM.

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