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Grete Waaseth, Roar Moe, Royal D. Heins, and Svein O. Grimstad

Varying photothermal ratios (PTR) were supplied to Salvia ×superba Stapf `Blaukönigin' during pre-inductive vegetative development with the exception of a short germination period under uniform conditions. In addition, both unvernalized plants and plants receiving a saturating vernalization treatment of 6 weeks at 5 °C were given two photosynthetic photon flux (PPF) levels (50 or 200 μmol·m-2·s-1) during subsequent inductive 16-hour long days. There were no effects of PTR treatments during vegetative development on subsequent flowering. However, the higher PPF level during inductive long days significantly accelerated floral evocation in unvernalized plants, lowering the leaf number at flowering. The effect was practically negligent after the vernalization requirement was saturated. In a second experiment, varying periods (4, 7, 10, and 14 days or until anthesis) at a PPF of 200 μmol·m-2·s-1 during 20-hour days were given at the beginning of a long-day treatment, either with or without preceding vernalization treatment. Flowering percentage increased considerably as the period at 200 μmol·m-2·s-1 was extended compared with plants grown at a lower PPF of 50 μmol·m-2·s-1. However, the leaf number on flowering plants was not affected, except in unvernalized plants receiving the highest PPF continuously until anthesis, where leaf number was reduced by almost 50%. We propose that the PPF-dependent flowering is facilitated either by the rate of ongoing assimilation or rapid mobilization of stored carbohydrates at the time of evocation. Abortion of floral primordia under the lower PPF (50 μmol·m-2·s-1) irrespective of vernalization treatment indicates that the assimilate requirement for flower bud development is independent of the mechanism for floral evocation.

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John E. Erwin, Royal D. Heins, and James E. Faust

Nephrolepis exaltata (L.) Schott `Dallas Jewel' plants were grown for 92 days under 16 day/night temperature (DT/NT) regimes and two photoperiods for a total of 32 environments. Temperatures ranged from 15 to 30 ± 1.5C. Photoperiod was either 9 hours (short days) or 9 hours plus a 4-hour night interruption (long days) using incandescent lamps. Photoperiod had no significant effect on either morphology or development rate. Frond length and leaflet count per frond were highly correlated with the average daily temperature (ADT). Frond length increased from 9.3 to 21.9 cm and leaflet count increased from 21 to 42 leaflets per frond as ADT increased from 15 to 30C. Solon count and frond orientation were highly correlated with the weighted difference (WDIF) between DT and NT. The weighted difference between DT and NT was equal to: (DT × photoperiod) - (NT × scotoperiod). The scotoperiod was inclusive of the night interruption. Stolon count increased as the weighted NT increased relative to the weighted DT, i.e., as WDIF decreased. In contrast, frond angle relative to the soil surface, i.e., frond orientation, increased as WDIF increased. Frond unfolding rate and total plant dry weight increased as temperature increased to ≈ 25C, then decreased.

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Royal D. Heins, Nathan Lange, and Thomas F. Wallace Jr.

Ageratum, begonia, marigold, and salvia seedlings in plug cells were stored in coolers to determine the effects of temperature, light, and storage time on growth and forcing time of seedlings after transplanting, and to determine the optimum storage temperatures for each crop. Photosynthetic photon flux densities of 0, 1, and 5 μmol·m-2.s-1 were combined with temperatures of 0.0, 2.5, 5.0, 7.5, 10.0, and 12.5C to create 18 storage environments. Sample plants were removed from each treatment at 1-week intervals for 6 weeks, and were forced into flower. In all four species, temperatures of 0.0 and 2.5C caused chilling injury and then death as plants were stored for progressively longer periods. Storage at 0.0 and 2.5C also delayed flowering when chilling injury was not severe enough to cause death. In general, plants stored better in the light than in darkness. Darkness tended to limit the time seedlings could be stored, but for each crop, the addition of just 1 μmol·m-2.s-1 extended the storage durations to 6 weeks at one or more temperatures. Storage of all four species was possible for 6 weeks, but there were significant variations between the temperatures and storage durations each species could tolerate. Optimal temperatures were 5-7.5C for begonia, 5C for marigold, and 7.5C for salvia and ageratum.

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James E. Faust, Sven Verlinden, and Royal D. Heins

Rapid reduction in temperature for two to three hours starting at sunrise reduces stem elongation compared to elongation of plants maintained under constant temperatures during the day. This experiment was designed to determine if syringing plants with water at sunrise would substitute for a reduction in air temperature or enhance the response to the drop in temperature. Easter lily (Lilium longiflorum Thumb.) plants were exposed to constant 20°C or to 20°C and then 16°C for a 3-hr period following sunrise. Half the plants in each temperature regime were syringed at 30-minute intervals with 20°C water for 3 hr starting 20 minutes before sunrise. Shoot-tip temperature during the three-hr pulse time averaged 20.0 and 17.3°C for the dry plants and 17.3 and 14.7°C for the syringed plants. Total elongation for the dry plants at 20°C was 30 cm and for the temperature-pulsed plants, 4.8 cm less; for the syringed plants, 3.3 and 5.8 cm less, respectively. While shoot-tip temperature of dry plants averaged 0.9°C above air temperature during the remaining hours of the day, syringed plants averaged 1.0°C cooler than the same air temperature even though plants had dried. The data indicate the reduction in stem elongation from a low-temperature pulse at sunrise can be enhanced by evaporative cooling.

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Shi-Ying Wang, William H. Carlson, and Royal D. Heins

The effect of 6 weeks of storage at 2.5, 5.0, 7.5, 10.0, or 12.5°C in a glass greenhouse was determined on 11 vegetatively propagated annual species. Fresh weight (total, shoot, and root) and height of 30 plants per species in each storage temperature were measured at the end of storage. Another 30 plants were transplanted into 15-cm pots (three plants per pot) and grown under natural light in a 20°C glass greenhouse for 3 weeks. Three species showed chilling injury or died during storage at ≤7.5°C. Plant height and shoot fresh weight at the end of storage for most species increased linearly as storage temperature increased. Storage temperature did not affect the net increase in height or weight significantly during recovery growth, except for plants that exhibited chilling injury at the end of storage.

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Royal D. Heins, Thomas F. Wallace Jr., and Susan S. Han

Chlorosis of Easter lily (Lilium longiflorum) lower leaves causes significant economic loss. Lily plants growing in 15-cm pots were sprayed 30, 60, or 90 days after emergence or at 60 and 90 days after emergence with 25 to 100 ppm each of benzyladenine and GA4+7 from Promalin (Abbott Chemical Co.) and were grown pot-to-pot until flower. Chlorotic leaf count at flower decreased as Promalin concentration increased; plants sprayed at 60 days had the smallest chlorotic leaf count. Chlorotic leaves at flower varied from 28% for control plants to 10% for plants sprayed with 100 ppm at 60 days and from 36% to 17% 3 weeks later, respectively. The Promalin sprays promoted significant stem elongation, but differences in height at flower were only 2 cm. Plants sprayed with 100 ppm at 30 days averaged one deformed flower per plant; plants sprayed at 60 days and 60 and 90 days averaged 0.0 and 0.1 deformed flower per plant, respectively. Additional trials in which only the lower part of the plant was sprayed prevented any chlorotic leaves without any significant effect on final height or flower bud quality.

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Beth A. Fausey, Royal D. Heins, and Arthur C. Cameron

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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Shi-Ying Wang, William H. Carlson, and Royal D. Heins

Argeranthemum frutescens `Butterfly' and `Sugar Baby', Brachycome hybrid `Ultra', Helichrysum bracteatum `Golden Beauty', Scaevola aemula `New Wonder',Supertunia axillaris hybrids `Kilkenny Bells' and `Pink Victory', Sutera cordata `Mauve Mist' and `Snowflake', and Verbena hybrid `Blue' were grown in a glass greenhouse maintained at 20°C under seven different photoperiods (10-, 12-, 13-, 14-, 16-, 24-hr, and 4-hr night interruption). Black cloth was pulled at 1700 and opened at 0800 HR; incandescent lamps provided 2 μmol·m–2·s–1 to extend light hours to the designed photoperiods. Seedlings were pinched 3 days after transplant. Responses to photoperiod were clearly species-dependent. The tested species can be classified into three groups: 1) stem elongation and flowering were promoted in the long-day treatment (A. frutescens and S. axillaris hybrids), 2) only stem elongation was promoted in the long-day treatment (S. aemula, H. bracteatum, and B. hybrid), and 3) neither flowering nor stem elongation were affected by photoperiod (S. cordata and V. hybrid).

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Mark P. Kaczperski, Royal D. Heins, and William H. Carlson

Methods of cold storage for rooted cuttings of three cultivars of Pelargonium ×hortorum Bailey were examined. Cuttings were stored from 0 to 10°C for 7 to 56 days. Treatments included packing the cuttings in ice, storing them under irradiance levels of 0 or 50 μmol·m–2·s–1, applying fungicides, varying cutting developmental stages, and varying the day temperatures. Cuttings packed in ice showed signs of chilling injury within 7 days and died. Applications of etridiazole and thiophanate-methyl or metalaxyl and thiophanate-methyl drenches or fosetyl-Al spray did not improve storage performance of the cuttings. Roots of cuttings held 7 additional days in the propagation area before storage grew faster after storage than those of cuttings with less time in the propagation area, but flowering time was not affected. Maintaining night temperatures at 5°C while allowing day temperatures to rise to 10°C delayed flowering by 6 days compared to maintaining a constant 5°C. Rooted cuttings held at 5°C under 50 μmol·m–2·s–1 irradiance for 9 hours each day could be stored up to 56 days with only a 2-day delay in flowering compared to unstored cuttings. Chemicals used were 5-ethoxy-3-trichloromethyl-1,2,4-thiadiazole (etridiazole); thiophanate-methyl (dimethyl[1,2-phenylene)bis(iminocarbonothioyl)]bis[carbamate]) (thiophanate-methyl); N-(2,6-dimethylphenyl)-N-methoxyacetyl) alanine methyl ester (metalaxyl); aluminum tris (O-ethyl phosphonate) (fosetyl-Al).

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Genhua Niu, Royal D. Heins, Arthur Cameron, and Will Carlson

The effects of temperature on flower size and number of flower buds of Campanula carpatica Jacq. 'Blue Clips', 'Deep Blue Clips', and Campanula 'Birch Hybrid' were investigated in four temperature and light-transfer experiments. In year 1, 'Blue Clips' and 'Birch Hybrid' plants were grown initially at 20 °C and then transferred at visible flower bud (VB) to 14, 17, 20, 23, or 26 °C until flower (Expt. 1). In Expt. 2, 'Blue Clips' and 'Birch Hybrid' plants were transferred from 14 to 26 °C or from 26 to 14 °C at various intervals after flower induction. Flower size of both species was negatively correlated with average daily temperature (ADT) after VB; flowers on plants grown at 14 °C were 35% larger than those on plants grown at 26 °C. In contrast, temperature before VB had only a small effect on final flower size in both species, although flower diameter of 'Birch Hybrid' plants grown at constant 26 °C was 20% smaller than that of the plants grown initially at 20°C and then transferred to VB to 26 °C. For both species, the longer the exposure to high temperature after VB, the smaller the flowers. Number of flower buds at flower in 'Birch Hybrid' decreased as ADT after VB increased. In year 2, 'Deep Blue Clips' plants were grown at constant 20 °C under high or low daily light integral (DLI, 17 or 5.7 mol·m-2·d-1) until VB, and then transferred to 14, 17, 20, 23, or 26 °C under high or low DLI (Expt. 3). In Expt. 4, 'Deep Blue Clips' plants were grown at 14, 17, 20, 23, or 26 °C until VB, and then transferred to constant 20 °C under high or low DLI until flower. Flower size (petal length) was negatively correlated with ADT both before and after VB, while flower bud number was negatively correlated with the ADT only after VB, regardless of DLI. In both experiments, petal length decreased by 0.3 to 0.5 mm per 1 °C increase in ADT before or after VB. Flowers were larger and more numerous under high than under low DLIs after VB, regardless of the DLI before VB.