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Four phases of development from emergence to anthesis of the opium poppy (Papaver somniferum L.) are recognized based on transfer studies using 9- and 16-hour photoperiods: a photoperiod-insensitive juvenile phase (JP), a photoperiod-sensitive inductive phase (PSP), a photoperiod-sensitive postinductive phase (PSPP), and a photoperiod-insensitive postinductive phase (PIPP). The objective of this experiment was to determine how the durations of the photoperiod-sensitive phases changed when the plants were exposed to different photoperiods. Plants were grown in lamplit growth chambers with a 12-hour thermoperiod of 25 °C day/20 °C night. They were transferred from a noninductive 9-h to an inductive 12-, 14-, or 16-hour photoperiod or vice versa at 1- to 4-day intervals to determine the durations of the four phases. The average number of days to flower by plants grown continuously in a 16-hour photoperiod was 32 days. Days to flower were delayed by 10 days in the 14-hour photoperiod and by 36 days in the 12-hour photoperiod. The durations of the four phases were not equally affected by photoperiod. The first three phases were photoperiod-dependent, the photoperiod effect being nonlinear. The durations of JP, PSP, and PSPP were 3, 5, and 17 days in the 16-hour; 4, 8, and 23 days in the 14-hour; and 7, 14, and 40 days in the 12-hour photoperiod, respectively. The final phase was not sensitive to photoperiod (i.e., PIPP lasted 7 days regardless of photoperiod). Based on these results, we conclude that the so-called juvenile phase cannot be regarded as photoperiod-insensitive. To model the development of opium poppy under field conditions, a knowledge of daylength as early as seedling emergence may be necessary. The number of inductive cycles needed for floral induction and the rate of floral development largely depend on the photoperiod experienced.

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Photoperiod-sensitive (short day) plants were found in okra [Abelmoschus esculentus (L.) Moench] PI 291124. These plants did not flower at Charleston, S.C., until mid-October. Segregation of populations derived from crosses with ‘Clemson Spineless’ (CS) indicated that photoperiod sensitivity was conditioned by a single recessive gene. Inheritance of hirsute seed, found in PI 172677, was determined by 2 separate genetic systems. The F1 of PI 172677 (hirsute) × ‘C S’ (glabrous) had hirsute hila and glabrous testae. In the F2, when data from seed parts were analyzed separately, hirsute hila was conditioned by 2 dominant genes, and glabrous testae was conditioned by 2 other dominant genes. When data on both seed parts were combined and independent assortment was assumed, 4 expected phenotypes were missing in the F2. Indirect evidence from the F2 and backcross populations indicated that there were linkages among the alleles which determine presence or absence of trichomes on okra seed. The possible linkage groups are described. An albino mutant, found in progeny of irradiated ‘CS’, was conditioned by a single recessive gene. The gene symbols sd and a are proposed for the genes conditioning the short day response and the albino mutant, respectively; the genes conditioning hirsute seed will not be named until linkage relationships can be resolved.

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Petunia × hybrida Vilm. cvs. `Purple Wave', `Celebrity Burgundy', `Fantasy Pink Morn', and `Dreams Red' were treated with temperature and photoperiod treatments for different lengths of time at different stages of development during the first 6 weeks after germination. Plants were grown with ambient light (≈8–9 hr) at 16°C before and after treatments. Flowering was earliest and leaf number below the first flower was lowest when plants were grown under daylight plus 100 μmol·m–2·s–1 continuous light (high-pressure sodium lamps). Flowering did not occur when plants were grown under short-day treatment (8-hr daylight). Plants grown with night interruption lighting from 2200–0200 HR (2 μmol·m–2·s–1 from incandescent lamps) flowered earlier, and with a reduced leaf number compared to plants grown with daylight + a 3-hr day extension from 1700–2000 HR (100 μmol·m–2·s–1 using high-pressure sodium lamps). Plant height and internode elongation were greatest and least in night interruption and continuous light treatments, respectively. `Fantasy Pink Morn' and `Purple Wave' were the earliest and latest cultivars to flower, respectively. Flowering was hastened as temperature increased from 12 to 20°C, but not as temperature was further increased from 20 to 24°C. Branching increased as temperature decreased from 24 to 12°C. Implications of data with respect to classification of petunia flower induction and pre-fi nishing seedlings are discussed.

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Growth chamber studies were conducted to determine growth responses of sweetpotato [Ipomoea batatas (L.) Lam) to differing photoperiods (PP) when grown by use of NFT. Four vine cuttings (15 cm length) of GA Jet and TI-155 were grown for 120 days at 12/12, 15/9, 18/6, and 21/3 light/dark PP. Irradiance averaged 427 umol m-2 s-1, with day/night temperatures of 28/22C and 70% RH. A modified half Hoagland's solution was used. Number of storage roots/plant, and storage root fresh and dry weights for GA Jet increased as PP increased from 12 to 21 h, while storage root fresh and dry weights for TI-155 increased up to 18 h PP but declined at 21 h PP. Storage root number/plant for TI-155 declined at 15 h PP but was higher at both 18 and 21 h PP. Highest foliage dry weight for GA Jet was obtained at 21 h PP while that for TI-155 was obtained at 18 h PP. Leaf area index (LAI) for GA Jet increased with increased PP, while LAI for TI-155 increased with increased PP up to 18 h then declined at 21 h PP.

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Proper acclimation of onion (Allium cepa L.) seedlings can enhance winter freeze survival; therefore, the effects of photoperiod-temperature combinations, photoperiod, and plant age on the cold hardiness of short-day onions were investigated. Following acclimation at various photoperiod-temperature regimes, different-aged plants were frozen to various subzero temperatures in an ethylene glycol bath and evaluated for cold hardiness. Older plants were more cold hardy than younger plants. An 11-hour photoperiod-decreasing temperature (20/15 to 10/5C day/night) treatment improved plant cold hardiness over other photoperiod-temperature regimes. Various photoperiods (8-, 11-, 14-, and 24-hour) applied during a 14-day, 3C acclimation treatment before freezing had little effect on plant cold hardiness. However, day 7 foliar and day 14 root evaluations indicated that 81-day-old plants given an 8- or 11-hour photoperiod during the 3C acclimation treatment were less cold hardy than older plants (91 or 112 days) given the same acclimation photoperiod.

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Cuttings of young potato plants (Solanum tuberosum L.) were used as a technique for evaluating the influence of temperature and photoperiod on the degree of tuber induction. Growth chambers were used to create four combinations of two air temperature regimes (“hot”, 30C day/25C night, or “cool”, 20C day/15C night) and two photoperiods (“long photoperiod”, 16 hr of light, or “short photoperiod”, 10 hr of light). The six cultivars and clones tested exhibited varying degrees of induction. Early maturing cultivars, such as ‘Norchip’ and ‘Cl-884’, were less affected by increased temperature with short photoperiod or by longer photoperiod under cool temperatures than were other cultivars. Raising the temperature under short photoperiod caused a reduction of about 50% in tuber dry weight from cuttings of the late-maturing ‘Katahdin’. Long photoperiod intensified the effects of higher temperature in reducing induction, especially with later-maturing cultivars such as ‘Katahdin’ and ‘Désirée’.

Open Access

‘UC Eclipse’, a photoperiod-insensitive cultivar of strawberry ( Fragaria × ananassa Duchesne), was developed and released by the University of California, Davis (UC Davis) College of Agriculture & Environmental Sciences for summer

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

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Abstract

Growth and flowering of bleeding heart were promoted by 14 to 24 hour photoperiods or light interruptions in the middle of the night. Cold treatment of crowns promoted growth and flowering at short photoperiods. Light at 9 klx promoted growth and inflorescence formation, but greater intensities were required to achieve anthesis. Growing temperatures of 15-22.5°C were most desirable.

Open Access

Campanula medium L. `Champion Blue' (CB) and `Champion Pink' (CP) and Lupinus hartwegii Lindl. `Bright Gems' (LH) were grown in 8- or 16-h initial photoperiods, transplanted when two–three, five–six, or eight–nine nodes developed and placed under 8-, 12-, or 16-h final photoperiods. Greatest flowering percentage (100%) for CB and CP occurred when plants with two–three nodes were grown in the 16-h final photoperiod. The lowest flowering percentage for CB (3.3%) and CP (15.7%) resulted from plants grown in the 8-h photoperiod continuously (initial and final). CB and CP stem lengths (49.8 cm) were longest when grown in the 8-h photoperiod continuously and shortest with the 16-h initial and 8-h final photoperiods for CB (26.5 cm) and the 16-h photoperiod continuously for CP (25.4 cm). Fewest days to anthesis, 134 days for CB and 145 days for CP, resulted from the 16-h photoperiod continuously and greatest (216 days) from the 8-h photoperiod continuously. LH plants had a high flowering percentage (99.6%) regardless of photoperiod or transplant stage. Stem lengths were longest (60.1 cm) for LH plants exposed to the 16-h photoperiod continuously and shortest (46.2 cm) when exposed to the 8-h photoperiod continuously. LH exhibited a curvilinear response for days to anthesis with the 16-h final photoperiod producing the shortest crop time (166 days) and the 12-h final photoperiod producing the longest crop time (182 days). The experiment was repeated in 1998/1999 with high intensity discharge (HID) lighting during the initial photoperiod which increased plant quality.

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