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Ami N. Erickson and Albert H. Markhart III

Reduction of floral number in Capsicum annuum has been observed during growth at high temperature. To determine whether decreased flower production or increased flower abscission is a direct response to high temperatures or a response to water stress induced by high temperatures, we compared flowers and fruit produced and flowers aborted to leaf growth rate, osmotic potential, stomatal conductance, and chlorophyll fluorescence of two cultivars. To determine the stage(s) of floral development that are most sensitive to high temperatures, flower buds were wax-embedded and examined at each stage of development during heat treatment. Rate of floral development also was examined. At first visible floral bud initiation, plants were transferred to each of three controlled environment growth chambers with set temperatures and vapor pressure deficits (VPD) of 25°C, 1.1 kPa; 33°C, 1.1 kPa; and 33°C, 2.1 kPa. Flower bud production and leaf growth rate were not significantly affected by high temperatures. Pepper fruit set, however, was inhibited at 33°C at either VPD. Preliminary water relations data suggested that water potentials were more negative under high temperature conditions. Differences in leaf fluorescence were statistically significant for temperature treatments, but not for VPD. Temperature is the primary factor in the decrease of fruit production in pepper. Decreased production is due to flower abortion and not to decreased flower initiation or plant growth.

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Erik S. Runkle, Royal D. Heins, Arthur C. Cameron, and William H. Carlson

Thirty herbaceous perennial species were treated at 5°C for 0 or 15 weeks. Critical photoperiods for flower initiation and development with and without a cold treatment were determined. Photoperiods were 10, 12, 13, 14, 16, or 24 hours of continuous light or 9 hours plus a 4-hour night interruption. Continuous photo-periodic treatments consisted of 9-hour natural days extended with light from incandescent lamps. Species were categorized into nine response types based on the effects of cold and photoperiod on flowering. Plants had three flowering responses to cold treatment: obligate, facultative, or none. The perennials were obligate long-day, facultative long-day, or day-neutral plants. For example, Campanula carpatica `Blue Clips' had no response to cold and was an obligate long-day plant requiring photoperiods of 16 hours or longer or night interruption for flowering. Rudbeckia fulgida `Goldsturm' had a facultative response to cold and required photoperiods of 14 hours or longer or night interruption for flowering. Veronica longifolia `Sunny Border Blue' had an obligate cold requirement and was day-neutral. Some species responded differently to photoperiod before and after cold. Leucanthemum ×superbum `Snow Cap' flowered as an obligate long-day plant without cold and as a facultative long-day plant after cold. Response categories are discussed.

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James E. Faust and Royal D. Heins

Quantum sensors were placed at plant canopy height inside and outside a glass greenhouse. Photosynthetic photon flux (PPF) was measured during September for a 3-hour period near sunrise and sunset, which were determined from US Naval Observatory Circular #171. Under clear skies, the PPF at the canopy exceeded 0.25 μmol·m-2·s-1 for nearly 20 minutes before sunrise through 20 minutes after sunset. Under heavy overcast, the duration was only 5 minutes before sunrise through 5 minutes after sunset. The PPF at the canopy reached 0.25 μmol·m-2·s-1 approximately 12 minutes later in the morning and 12 minutes earlier in the evening than it did outside the greenhouse. The length of the dark period perceived by plants in a greenhouse on September 21st (assuming plants perceive light at 0.25 μmol·m-2·s-1) can range from 11:37 (hr:min) during cloudy conditions to 11:15 during clear ones, a difference of 22 minutes. At 43°N latitude, the maximum difference in date of flower initiation because of an extended period of heavily overcast versus clear weather on a crop such as poinsettias would be one week since the night length during September increases by 3 minutes per day. The actual difference from year to year is probably less because a seven-day duration of heavily overcast weather is unlikely.

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Donglin Zhang, Allan M. Armitage, James M. Affolter, and Michael A. Dirr

Lysimachia congestiflora Wils. (Primulaceae) is a new crop for American nurseries and may be used as an annual in the north and a half-hardy perennial in the south. The purpose of this study was to investigate the influence of photoperiod, temperature, and irradiance on its flowering and growth. Three experiments were conducted with photoperiod of 8, 12, 16 hrs day-1, temperature of 10, 18, 26C, and irradiance of 100, 200, 300 μmol m-2s-1, respectively. Plant.9 given long day photoperiod (16 hours) flowered 21 and 34 days earlier, respectively, than plants at 12 sad 8 hour photoperiods. Plants under long day treatment produced more flowers than those at 8 and 12 hours. Plant dry weight did not differ between treatments, but plants grown in the long day treatment produced fewer but larger leaves. Total plant growth increased as temperature increased, but lower temperature (10C) decreased flower initiation and prevented flower development, while high temperature (26C) reduced the longevity of the open flowers. Flowering was accelerated and dry weight increased as plants were subjected to high irradiance levels. The results suggest that Lysimachia congestiflora is a quantitative long day plant. It should be grown under a photoperiod of at least 12 hours at a temperature of approximately 20C. Low light areas should be avoided and supplemental lighting to provide the long days may improve the plant quality.

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Donglin Zhang, A.M. Armitage, J.M. Affolter, and M.A. Dirr

Arabis sturii Mottet (Brassicaceae) has potential as a new crop for American nurseries and may be used as a perennial pot plant. Cold treatment was required for flowering of Arabis sturii and a 6-week cold treatment resulted in the greatest number of racemes and flowers per plant. Increasing or decreasing length of cold treatment resulted in less flowers per plant. Plant height increased as duration of cold treatment increased. Photoperiod had a significant effect on flowering and growth only after plants received 3 weeks or more cold treatment. All plants given a 16-h photoperiod flowered, while only 50% and 80% flowered under an 8- or 12-h photoperiod, respectively. A 16-h photoperiod shortened the time to production of flower buds and anthesis and the greatest difference occurred after the 9-week cold treatment. At the 6-week cold treatment, number of flowers per plant different significantly between long (145 flowers) and short day (59). The effect of photoperiod on number of flowers per plant became less as cold treatment increased or decreased. Although photoperiod did not induce flower initiation, it had a tremendous effect on flower development. Many more flowers were produced and plants were taller as photoperiod increased. No significant difference was found in plant dry weight.

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Jianying Peng and Peter Hirst

Buds were sampled from nonflowering spurs on 1-year-old wood of 10 apple cultivars during the 2004 growing season and dissected to determine floral commitment and morphogenesis. Dissected buds were classified into five stages based on floral bud morphogenesis. The 10 cultivars differed in their patterns of floral commitment and morphogenesis. At the end of the growing season, the proportion of floral buds was 30% to 100% depending on cultivar. The probability of observing doming, indicating floral commitment, was from 5% to 50% depending on cultivar, with `NJ90' (50%), `Zestar' (30%), and `CQR10T17' (30%) rated among the highest. The lowest probability (5%) was with `Ambrosia', `Pinova', and `Silken'. The time of a peak of floral commitment was earliest in `Delblush' and `CQR10T17' and latest in `Sundance'™ and `Pinova'. Most cultivars exhibited a single peak of floral commitment, except for `Pink Lady' in which two peaks were present. The duration of the process of flower initiation was from 20 to 43 days depending on cultivar. The timing of floral commitment and morphogenesis was not related either to blooming date, or to fruit harvest time of the cultivar.

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Meriam G. Karlsson

The rate of leaf unfolding as a function of temperature was determined for Begonia × hiemalis Fotsch under long-day (16 hours of light) conditions before flower initiation. Irradiance was maintained at 280 ± 20 μmol·m–2·s–1 (16.1 mol·m–2·day–l). The two cultivars Hilda and Ballet had similar rates of leaf unfolding in the range from 13 to 28C. The rate increased to a maximum of 0.116 leaves/day at 21C and then decreased at higher temperature. The following quadratic function (where T is the temperature in °C) was selected to describe initial long-day leaf unfolding rate in B. × hiemalis: leaves/day = -0.2083 + 0.03145 × T – 0.0007631 × T2, (r2 = 0.97). The leaf unfolding response to temperature varied for plants of `Hilda' and `Ballet' during short days (10 hours of light) following the initial long-day period. Plants of `Ballet' continued to unfold leaves at a similar rate as under initial long photoperiods, while the leaf unfolding rate for `Hilda' decreased to half the rate observed under long days.

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James E. Faust and Royal D. Heins

The effects of temperature and irradiance on flower initiation and development were quantified to provide a basis for an inflorescence development model. The percentage of leaf axils forming an inflorescence increased as the daily integrated PPF increased from 1 to 4 mol m-2 d-1, while the rate of inflorescence development was a linear function of temperature from 18 to 26C. The appearance of a visible flower bud in the leaf axil was correlated with leaf blade length of the subtending leaf. Mathematical functions were used to describe leaf blade length at the time of visible flower bud as a function of temperature and irradiance, and also to describe the influence of temperature on the rate of leaf extension. The time of visible flower bud in the leaf axil was then predicted by measuring the current length of the subtending leaf blade and estimating the time required for the leaf blade to extend to the length required for visible flower bud appearance. A phasic development scale was used to describe the developmental status of an inflorescence from visible flower bud to anthesis. A model was then created which predicted time to anthesis based upon temperature and the current stage of inflorescence development.

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Yolenda Perez, Douglas Delgado, and Juan E. Manzano

Phenologycal studies of melon hybrids (Chando, Concorde, Explorer, and Durango) were made through the parameter days to enmergency, type of flowers, days to initiate flowering after sowing, flowering period until first fruit appeared, first cycle fruit formation until new cycle, and days from sowing until the first and final harvest. Chando and Concorde hybrids germinated 4 days after sowing, and Explorer and Durango hybrids germinated 1 day later. All hybrids presented andromonoic flowers. The first flower bottom was present at 25 days after sowing, especially in the hybrid Concorde, while for Explorer and Durango hybrids, it was 26 days. The period of time from flower initiation until the first fruit appeared for Concorde and Chando was 5 days, while for Explorer and Durango hybrids, it was 7 days. Fruit formation occurred in the first cycle and had a duration of 9 days from Concorde. For Chando, Explorer, and Durango, the formation of first fruit group (first cycle) was 12 days. The period of time from sowing until first harvest was 61 days for Concorde and 69 days for the final harvest and from 63 to 72 days, respectively, for the Chando hybrids. For Explorer and Durango, it was 67 to 78 days, respectively.

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Harlene Hatterman-Valenti*

Greenhouse studies were conducted to evaluate simulated drift injury to annual bedding plants. Dahlia, gazania, geranium, marigold, petunia, and salvia in the early stages of flowering were sprayed with either 2,4-D (dimethylamine salt) or dicamba (diglycolamine salt) at rates one-fifth, one-tenth, or one-twentieth the lowest labeled rate of for turfgrass. Interactions between species by time, species by treatments, and treatments by time were significant for visual injury. Species sensitivity from most sensitive to least sensitive was marigold > dahlia ≫ geranium = petunia > gazania = salvia. Dahlia was more sensitive to dicamba than 2,4-D while the opposite was true for marigold. Petunia flower initiation was reduced as dicamba or 2,4-D rate was increased. The duration of the trial may have limited flowering differences among treatments with the remaining species. Dahlia loss of apical dominance as an injury response was greater with dicamba than 2,4-D. Typical injury symptoms for dahlia included stem, leaf, and petiole epinasty along with multiple shoot growth. Gazania injury included slight leaf rolling and leaf stretching. Geranium injury included leaf curling and fewer flowers per cluster. Marigold injury included leaf node swelling and stem wall rupture with massive cellular proliferation. Petunia injury included stem and pedicel epinasty, curling of the outer portion of the corolla, and lower flower production. Salvia injury included stunting, slight flower stem curvature, and partial dieback of the terminal raceme.