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102 POSTER SESSION 4F (Abstr. 224–233) Photoperiod/Temperature/Growth—Floriculture

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Photoperiod is an environmental signal that controls bud dormancy and break, tuber formation, and flowering. A photoperiodic response, such as flowering, is determined primarily by the duration of the dark period (skotoperiod). Based on

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Flowering in strawberry is known to be significantly affected by temperature and photoperiod ( Kumakura and Siilsiildo, 1995 ), and the floral initiation of strawberry is regulated by a complex set of environmental and physiological cues ( Awang and

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daily endogenous rhythms, also known as circadian rhythms ( Dodd et al., 2005 ). GI was found to induce flowering in long-day (LD) photoperiods by regulating miR172 accumulation ( Jung et al., 2007 ). Plants having a defect in maintaining circadian

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, 1992 ; Gutterman, 2000 ; Hilhorst and Toorop, 1997 ). Some of the frequently studied environmental factors are temperature, water availability, light (quality and photoperiod), altitude, and mineral nutrition. In most studies where photoperiod effects

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higher crop dry matter and nitrogen at flowering stage, which was associated with higher final grain yield ( Ferrise et al., 2010 ). Further studies have shown that the effects of different sowing dates on the changes caused by temperature and photoperiod

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Abstract

Gypsophila paniculata L. cv. Bristol Fairy flowered only under long photoperiods. Neither 5°C storage up to 8 weeks nor weekly GA3 sprays at concentration from 50 to 2,000 mg/liter induced flowering at short photoperiods. Established shoots with 12 nodes flowered after 3 weeks of 24 hours photoperiod induction, but young shoots with 5 nodes (newly pinched plants) did not flower after 3 weeks of induction. Critical photoperiod of several selections of ‘Bristol Fairy’ ranged from 12-18 hours. Inadvertent selection of clones with longer critical photoperiods appears to be responsible for poor winter flowering in Florida.

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To determine the flowering requirements of Rudbeckia fulgida Ait. `Goldsturm', plants were grown under 9-hour photoperiods until maturity, then forced at 20 °C under one of seven photoperiods following 0 or 15 weeks of 5 °C. Photoperiods consisted of a 9-hour day that was extended with incandescent lamps to 10, 12, 13, 14, 16, or 24 hours; an additional treatment was a 9-hour day with a 4-hour night interruption (NI). Noncooled `Goldsturm' remained vegetative under photoperiods ≤13 hours, and essentially all plants flowered under photoperiods ≥14 hours or with a 4-hour NI. Flowering percentages for cooled plants were 6, 56, or ≥84 under 10-, 12-, or ≥13-hour daylengths and NI, respectively. Critical photoperiods were ≈14 or 13 hours for noncooled or cooled plants, respectively, and base photoperiods shifted from 13 to 14 hours before cold treatment to 10 to 12 hours following cold treatment. Within cold treatments, plants under photoperiods ≥14 hours or NI reached visible inflorescence and flowered at the same time and developed the same number of inflorescences. Fifteen weeks of cold hastened flowering by 25 to 30 days and reduced nodes developed before the first inflorescence by 28% to 37%. Cold treatment provided little or no improvement in other measured characteristics, such as flowering percentage and uniformity, flower number, plant height, and vigor.

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Five vegetatively propagated perennial species that received 0 or 15 weeks of cold treatment were placed under seven photoperiods (10-, 12-, 13-, 14-, 16-, 24-, and 4-hour night interruption). Cuttings were harvested every 3 weeks, and their number and total fresh weight were recorded. Cutting bases were dipped in a 1200 ppm IBA solution for 5 seconds, stuck in perlite, and placed under mist for 3 weeks. Results varied by species. Stock plants of Achillea `Moonshine' produced the most cuttings under a 12-hour photoperiod. Noncold treated Coreopsis verticillata `Moonbeam' only produced cuttings under photoperiods longer than or equal to 14 hours. Cold treated `Moonbeam' produced cuttings under all photoperiods in the first flush. Eighty percent of cuttings from the first flush of Phlox paniculata `Eva Cullum' rooted when taken from plants growing under the 10-hour photoperiod, but only 1.2 cuttings per plant were harvested; 2.5 cuttings per plant were taken from Phlox grown under the 24-h photoperiod, but only 20% rooted. Only stock plants of Sedum `Autumn Joy' receiving a 14-hour photoperiod produced significant numbers of vegetative shoots. Cutting production and rooting of Veronica `Sunny Border Blue' was not affected by photoperiod.

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The rooting efficiency of cuttings from three poinsettia cultivars were evaluated after regulating the photoperiod during the stock plant stage. `Freedom Red', `Monet', and `V-17 Angelika Marble' stock plants were exposed to an extended photoperiod and to natural day length during September 1995. `Freedom Red' cuttings rooted more quickly under an extended photoperiod compared to those under natural day length. Furthermore, root dry weight from these cuttings was greater than cuttings from stock plants grown under natural day length. `Monet' cuttings also rooted more quickly when the stock plants were under an extended photoperiod, and showed similar differences in root weight as `Freedom Red'. Cuttings from `V-17 Angelika Marble' were not influenced by photoperiod. Lighting stock plants to block flower initiation produces a higher quality cutting when propagation takes place after the critical day length for flowering has passed.

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