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James E. Faust and Royal D. Heins

The effects of supplemental lighting on vinca (Catharanthus roseus L.) plant temperature were quantified in greenhouses maintained at air temperatures of 15. 25, and 35C. High-pressure sodium (HPS) lamps delivering 100 μmol·m-2·s-1 PPF provided 73 W · m-2 of total radiation (400 to 50,000 nm) to lighted plants. Plant shoot-tip temperature was measured by using 40-gauge thermocouples. Relative to air temperature, plant shoot-tip temperature depended on the irradiance and vapor-pressure deficit (VPD). Irrespective of VPD, the additional irradiance absorbed by plants under the HPS lamps increased plant temperature 1 to 2°C. Under relatively low VPD conditions (1 kPa), plant temperature was greater than air temperature, while under high VPD conditions (4 to 5 kPa), temperature of both lighted and unlighted plants remained below air temperature throughout the day. Temperature of lighted plants however, remained 1 to 2°C above that of unlighted plants. Analysis of a degree-day model of vinca development showed hastened development associated with supplemental lighting could be explained by increased plant temperature rather than any specific photosynthetic effect.

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James E. Faust and Royal D. Heins

Poor lateral branching sometimes occurs when certain poinsettia (Euphorbia pulcherrima) cultivars are pinched. Two experiments were conducted to determine the effect of high temperatures on axillary bud development. In Expt. 1, `Red Sails' plants were grown in a high-temperature environment (HTE) of 27°C at night (8 hr) and 30°C (3 hr), 33°C (10 hr), and 30°C (3 hr) in the day for two months, then transferred to a 20°C environment. In Expt. 2, plants grown at 20°C were transferred into the same HTE described above for 0, 2, 4, 8, 16, or 32 days and were then moved back into the 20°C environment. Axillary buds were examined for viability at the end of each experiment. In Expt. 1, only 8% of the lateral buds forming in the HTE were viable, while 80% of the buds forming in leaf axils of leaves unfolding after the plants were transferred to the 20°C environment were viable. In Expt. 2, 80% of buds produced in axils of the first four leaves to unfold after the start of the experiment were viable in all the treatments. However, the percentage of viable buds in the axils of leaf numbers 5 to 8 was 100, 100, 100, 96, 56, and 0 for the plants placed in the HTE for 0, 2, 4, 8, 16, and 32 days, respectively. These data indicate day temperatures of 30 to 33°C adversely affect lateral shoot development of `Red Sails' poinsettia.

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James E. Faust and Royal D. Heins

Dendranthema ×grandiflorm (Ramat.) Kitamura `Powerhouse' plants were pinched to five nodes and grown in growth chambers at 35C day temperature (DT) and 14,17,21,24, or 27C night temperature (NT) to determine if NT influenced lateral shoot development on plants exposed to high DT. Vegetative cuttings were removed from two successive flushes of lateral shoots and evaluated for lateral shoot development after rooting and subsequent apex removal. Lateral shoot development was determined on a third flush of shoots that developed on the stock plants. The percentage of nodes that developed lateral shoots on stock plants or vegetative cuttings was not related to NT. The percentage of first-order, second-order, and third-order axillary nodes that developed a lateral shoot on the stock plants, averaged over all NT, was 76, 65, and 12, respectively. The percentage of nodes that developed lateral shoots on the first-order and second-order cuttings was 29 and 19, respectively. We concluded that cool NT were ineffective in preventing a decrease in lateral branching on plants grown under high (35C) DT conditions.

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Erik S. Runkle and Royal D. Heins

Environments with a low red (R, 600 to 700 nm) to far-red (FR, 700 to 800 nm) ratio (e.g., with high plant density) promote stem elongation, and a high R: FR suppresses it. While FR light promotes stem extension, it is also required for rapid, uniform flowering of many long-day plants. We investigated how a new FR filter [creating a FR-deficient (FRd) environment] influenced plug growth and subsequent flowering of pansy (Viola ×wittrockiana `Crystal Bowl Yellow'), petunia (Petunia ×hybrida `Carpet Pink'), impatiens (Impatiens wallerana `Accent Rose'), snapdragon (Antirrhinum majus `Liberty Scarlet'), and tomato (Solanum lycopersicon `Beefmaster'). One-week-old seedlings were placed under three filter treatments with 16-h photoperiods: the FRd filter, a neutral-density filter (N) that transmitted a similar PPF, and transferring plugs from the N to the FRd filter when leaves of each species began to touch (7 to 11 days later). The predicted phytochrome photoequilibria under the FRd and N filters was 0.80 and 0.72, respectively. After 25 to 35 days at 20 °C, node number and stem (or petiole for pansy) length were collected. Twenty plants of each species and filter treatment were then transferred to 4-inch pots and grown under natural photoperiods (14 to 15 h) at 20 °C until flowering. Compared to plants continually under the N filter, stem length under the FRd filter was significantly reduced in impatiens (by 11%), pansy (by 18%), petunia (by 34%), snapdragon (by 5%), and tomato (by 24%). Flowering of plants from plugs under the FRd filter was delayed by 2 to 3 days for snapdragon, petunia, and pansy. Filter treatment of plugs had no significant effect on flower number or plant height at flower.

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John E. Erwin and Royal D. Heins

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James E. Faust and Royal D. Heins

Axillary buds of African violet develop vegetative shoots or reproductive inflorescences. Vegetative axillary development results in a multiple-shoot plant and reduces plant quality. We determined the effect of temperature and plantlet size on axillary bud development. Plantlets were removed from leaf cuttings, graded according to stem diameter, directly stuck into pots 10 cm in diameter, and placed in greenhouses at 18, 22, or 26C. Vegetative development was related to temperature, plantlet size, and nodal position. The number of vegetative axillary shoots per plant decreased from 3.7 to 1.3; that of leaves per vegetative axillary shoot decreased from 10.3 to 4.8 as temperature increased from 18 to 26C. The eight to 10 basipetal nodes developed vegetative shoots or were devoid of axillary development. The percentage of leaf axils in which inflorescences developed increased from 14 on node eight to 100 on nodes 12 and higher. The larger plantlets at the time of transplant had 20% fewer vegetative axillary shoots, whereas reproductive inflorescence development was not affected by plantlet size.

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Erik S. Runkle and Royal D. Heins

For many plants, light quality has a pronounced effect on plant morphology; light with a low red (R, 600 to 700 nm) to far-red (FR, 700 to 800 nm) ratio promotes stem elongation and a high R: FR, or blue light (B, 400 to 500 nm), suppresses it. In addition, FR light is required for rapid flowering in some species, particularly for long-day plants. Our objective was to quantify how flexible spectral filters, which selectively reduce FR, B, or R, influence plant height and flowering of the quantitative long-day plants Pisum sativum L. `Utrillo' and Viola ×wittrockiana Gams. `Crystal Bowl Yellow'. Plants were grown at 20 °C with reduced FR, B, or R environments or with a neutral density control (C) filter. Calculated phytochrome photoequilebria were 0.78, 0.73, 0.71, or 0.46 for the altered FR, B, C, or R environments, respectively. All filter treatments transmitted a similar photosynthetic photon flux. Sixteen-hour photoperiods were created with natural daylight supplemented with high-pressure sodium lamps positioned above filters. Viola grown under the FR filter never reached 100% flowering within 8 weeks, and visible bud appearance was delayed by at least 17 days compared to all other filters. The R and B filters enhanced peduncle length by at least 25% compared to the C or FR filters. In Pisum, average internode length was 2.2, 2.9, 3.4, and 3.7 cm under the FR, C, B, and R filters, respectively, all statistically different. Fresh and dry shoot weights were similar under the C and FR filters but were at least 35% greater under the B filter and 35% lower under the R filter.

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Keith A. Funnell and Royal D. Heins

The postharvest quality of potted Asiflorum lily `Donau' (Lilium hybrid) was evaluated after plants were sprayed with 0, 50, 250, or 500 mg·L-1 (BA equivalent) of Promalin (GA4+7 to BA ratio was 1:1) or Accel (GA4+7 to BA ratio 1:10) and stored at 2 to 3 °C for 0, 10, or 20 days. As storage was prolonged, more leaves senesced once plants were removed for evaluation. Leaf senescence declined with increasing concentrations of either Promalin or Accel, but Promalin was more effective. Application of 250 mg·L-1 Promalin completely eliminated leaf senescence over the 20-day shelf-life evaluation period, irrespective of duration of cold storage. The treatments did not affect flower bud opening or plant height. Chemical names used: gibberellin (GA4+7); benzyladenine (BA).

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Erik S. Runkle and Royal D. Heins

Plastics that selectively reduce the transmission of far-red light (FR, 700 to 800 nm) reduce extension growth of many floricultural crops. However, FR-deficient (FRd) environments delay flowering in some long-day plants (LDPs), including `Crystal Bowl Yellow' pansy (Viola ×wittrockiana Gams). Our objective was to determine if FR light could be added to an otherwise FRd environment to facilitate flowering with minimal extension growth. In one experiment, plants were grown under a 16-hour FRd photoperiod, and FR-rich light was added during portions of the day or night. For comparison, plants were also grown with a 9-hour photoperiod [short-day (SD) control] or under a neutral (N) filter with a 16-hour photoperiod (long day control). Flowering was promoted most (i.e., percent of plants that flowered increased and time to flower decreased) when FR-rich light was added during the entire 16-hour photoperiod, during the last 4 hours of the photoperiod, or during the first or second 4 hours after the end of the photoperiod. In a separate experiment, pansy was grown under an FRd or N filter with a 9-hour photoperiod plus 0, 0.5, 1, 2, or 4 hours of night interruption (NI) lighting that delivered a red (R, 600 to 700 nm) to FR ratio of 0.56 (low), 1.28 (moderate), or 7.29 (high). Under the N filter, the minimum NI duration that increased percent flowering was 2 hours with a moderate or low R:FR and 4 hours with a high R:FR. Under the FRd filter, 2 or 4 hours of NI lighting with a moderate or low R:FR, respectively, was required to increase percent flowering, but a 4-hour NI with a high R:FR failed to promote flowering. Pansy appears to be day-neutral with respect to flower initiation and a quantitative LDP with respect to flower development. The promotion of reproductive development was related linearly to the promotion of extension growth. Therefore, it appears that in LDPs such as pansy, light duration and quality concomitantly promote extension growth and flowering, and cannot readily be separated with lighting strategies.

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Erik S. Runkle and Royal D. Heins

For many long-day plants (LDP), adding far red light (FR, 700 to 800 nm) to red light (R, 600 to 700 nm) to extend the day or interrupt the night promotes extension growth and flowering. Blue light (B, 400 to 500 nm) independently inhibits extension growth, but its effect on flowering is not well described. Here, we determined how R-, FR-, or B-deficient (Rd, FRd, or Bd, respectively) photoperiods influenced stem extension and flowering in five LDP species: Campanula carpatica Jacq., Coreopsi ×grandiflora Hogg ex Sweet, Lobelia ×speciosa Sweet, Pisum sativum L., and Viola ×wittrockiana Gams. Plants were exposed to Rd, FRd, Bd, or normal (control) 16-hour photoperiods, each of which had a similar photosynthetic (400 to 700 nm) photon flux. Compared with that of the control, the Rd environment promoted extension growth in C. carpatica (by 65%), C. ×grandiflora (by 26%), P. sativum (by 23%), and V. ×wittrockiana (by 31%). The FRd environment suppressed extension growth in C. ×grandiflora (by 21%), P. sativum (by 17%), and V. ×wittrockiana (by 14%). Independent of the R: FR ratio, the Bd environment promoted stem extension (by 10% to 100%) in all species, but there was little or no effect on flowering percentage and time to flower. Extension growth was generally linearly related to the incident wide band (100 nm) R: FR ratio or estimated phytochrome photoequilibrium except when B light was specifically reduced. A high R: FR ratio (i.e., under the FRd filter) delayed flower initiation (but not development) in C. carpatica and C.×grandiflora and inhibited flower development (but not initiation) in Vwittrockiana. Therefore, B light and the R: FR ratio independently regulate extension growth by varying magnitudes in LDP, and in some species, an FRd environment can suppress flower initiation or development.