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W. Garrett Owen, Qingwu Meng, and Roberto G. Lopez

Under natural short days, growers can use photoperiodic lighting to promote flowering of long-day plants and inhibit flowering of short-day plants. Unlike traditional lamps used for photoperiodic lighting, low-intensity light-emitting diode (LED) lamps allow for a wide array of adjustable spectral distributions relevant to regulation of flowering, including red (R) and white (W) radiation with or without far-red (FR) radiation. Our objective was to quantify how day-extension (DE) photoperiodic lighting from two commercially available low-intensity LED lamps emitting R + W or R + W + FR radiation interacted with daily light integral (DLI) to influence stem elongation and flowering of several ornamental species. Long-day plants [petunia (Petunia ×hybrida Vilm.-Andr. ‘Dreams Midnight’) and snapdragon (Antirrhinum majus L. ‘Oh Snap Pink’)], short-day plants [african marigold (Tagetes erecta L. ‘Moonsong Deep Orange’) and potted sunflower (Helianthus annuus L. ‘Pacino Gold’)], and day-neutral plants [pansy (Viola ×wittrockiana Gams. ‘Matrix Yellow’) and zinnia (Zinnia elegans Jacq. ‘Magellan Cherry’)] were grown at 20/18 °C day/night air temperatures and under low (6–9 mol·m−2·d−1) or high (16–19 mol·m−2·d−1) seasonal photosynthetic DLIs from ambient solar radiation combined with supplemental high-pressure sodium lighting and DE LED lighting. Photoperiods consisted of a truncated 9-hour day (0800–1700 hr) with additional 1-hour (1700–1800 hr, 10 hours total), 4-hour (1700–2100 hr, 13 hours total), or 7-hour (1700–2400 hr, 16 hours total) R + W or R + W + FR LED lighting at 2 μmol·m−2·s−1. Days to visible bud, plant height at first open flower, and time to first open flower (TTF) of each species were influenced by DLI, lamp type, and photoperiod though to different magnitudes. For example, plant height of african marigold and potted sunflower at first open flower was greatest under R + W + FR lamps, high DLIs, and 16-hour photoperiods. Petunia grown under R + W lamps, high DLI, and 10- and 13-hour photoperiods were the most compact. For all species, TTF was generally reduced under high DLIs. For example, regardless of the lamp type, flowering of african marigold occurred fastest under a high DLI and 10-hour photoperiod. Flowering of petunia and snapdragon occurred fastest under a high DLI, R + W + FR lamps, and a 16-hour photoperiod. However, only under high DLIs, R + W or R + W + FR lamps were equally effective at promoting flowering when used to provide DE lighting. Our data suggest that under low DLIs, flowering of long-day plants (petunia and snapdragon) occurs more rapidly under lamps providing R + W + FR, whereas under high DLIs, flowering is promoted similarly under either R + W or R + W + FR lamps.

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Kellie J. Walters, Allison A. Hurt, and Roberto G. Lopez

Foliage annuals are primarily grown for the aesthetic appeal of their brightly colored, variegated, or patterned leaves rather than for their flowers. Once foliage annuals become reproductive, vegetative growth of many species diminishes or completely ceases and plants can become unappealing. Therefore, the objectives of this study were to quantify how growth and development during production and stock plant cutting yield of bloodleaf (Iresine herbstii), Joseph’s coat (Alternanthera sp.) ‘Brazilian Red Hots’ and ‘Red Threads’, Persian shield (Strobilanthes dyerianus), and variegated potato vine (Solanum jasminoides) are influenced by photoperiod and night interruption (NI) lighting with or without far-red (FR) radiation. Photoperiods consisted of a 9-hour short day (SD) or a 9-hour SD extended to 10, 12, 13, 14, or 16 hours with red (R):white (W):FR light-emitting diode (LED) lamps (R:FR = 0.8) providing a total photon flux density (TPFD) of ≈2 µmol·m−2·s–1 of radiation. In addition, two treatments consisted of a 9-hour SD with a 4-hour NI from lamps containing the same R:W:FR or R:W LEDs (R:FR = 37.4). Bloodleaf plant and Joseph’s coat ‘Brazilian Red Hots’ and ‘Red Threads’ developed inflorescences or flowers under photoperiods ≤12 to 13 hours and were classified as obligate SD plants. Under LEDs providing R:W:FR radiation, stem elongation of reproductive bloodleaf and Joseph’s coat ‘Brazilian Red Hots’ and ‘Red Threads’ increased as photoperiod increased from 9 to 12 hours. In addition, stem elongation of bloodleaf, Joseph’s coat ‘Brazilian Red Hots’ and ‘Red Threads’, and Persian shield and growth index (GI = {plant height + [(diameter 1 + diameter 2)/2]}/2) of bloodleaf and Persian shield was significantly greater under NI with FR radiation than without FR radiation. Fewer or no cuttings were harvested from Joseph’s coat ‘Brazilian Red Hots’ and ‘Red Threads’ under photoperiods ≤12 or ≤13 hours, respectively. To prevent unwanted flowering of bloodleaf plant and Joseph’s coat, a photoperiod ≥14 hours or 4-hour NI must be maintained with LEDs providing either R:W or R:W:FR radiation, however; stem elongation is significantly reduced under R:W LEDs.

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Allison Hurt, Roberto G. Lopez, and Joshua K. Craver

In northern latitudes, the photosynthetic daily light integral can be less than 5 mol·m–2·d–1, necessitating the use of supplemental lighting (SL) to reduce bedding plant seedling production time and increase quality. Our objectives were 1) to quantify seedling quality and production time under continuous 16-h or instantaneous threshold SL, continuous low-intensity photoperiodic lighting (PL) for 16 or 24 hours with and without far-red light, or no electric lighting; and 2) to determine whether the described lighting treatments during propagation impact finished plant quality or flowering. Seeds of begonia (Begonia ×semperflorens) ‘Bada Bing Scarlet’, gerbera (Gerbera jamesonii) ‘Jaguar Deep Orange’, impatiens (Impatiens walleriana) ‘Accent Premium Salmon’, petunia (Petunia ×hybrida) ‘Ramblin Peach Glo’, and tuberous begonia (Begonia ×tuberosa) ‘Nonstop Rose Petticoat’ were sown in 128-cell trays and grown under either SL, PL, or no electric lighting (control). SL treatments consisted of high-intensity light-emitting diode (LED) or high-pressure sodium (HPS) lamps providing a photosynthetic photon flux density (PPFD) of either 70 µmol·m–2·s–1 on continuously for 16 h·d–1 or 90 µmol·m–2·s–1 based on an instantaneous threshold. PL treatments consisted of low-intensity red:white (R:W) or red:white:far-red (R:W:FR) lamps for 16 h·d–1 or R:W:FR lamps for 24 h·d–1. Seedlings of gerbera, impatiens, and petunia from each treatment were subsequently transplanted and finished in a common greenhouse environment. The highest quality seedlings were grown under SL compared with PL or control conditions. When comparing SL treatments, seedlings produced under HPS or LED SL using an instantaneous threshold were of equal or greater quality compared with those under continuous SL with a 16-h photoperiod. Although the greater leaf area and internode elongation under PL may give growers the perception that seedling production time is reduced, PL did not increase biomass accumulation and seedling quality. Petunia seedlings propagated under HPS lamps using an instantaneous threshold flowered 4 to 11 days earlier compared with the other SL treatments. In addition, petunia propagated under R:W:FR PL for 16 h·d–1 flowered 5 to 7 days earlier compared with LED SL and the other PL treatments.

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Christopher J. Currey, Roberto G. Lopez, and Neil S. Mattson

Energy accounts for one of the largest costs in commercial greenhouse (GH) production of annual bedding plants. Therefore, many bedding plant producers are searching for energy efficient production methods. Our objectives were to quantify the impact of growing annual bedding plants in an unheated high tunnel (HT) compared with a traditional heated GH environment at two northern latitudes. Ten popular bedding plants [angelonia (Angelonia angustifolia), vinca (Catharanthus roseus), celosia (Celosia argentea), dianthus (Dianthus chinensis), geranium (Pelargonium ×hortorum), petunia (Petunia ×hybrida), french marigold (Tagetes patula), viola (Viola ×cornuta), snapdragon (Antirrhinum majus), and osteospermum (Osteospermum ecklonis)] were grown both in an unheated HT and a glass-glazed GH with an 18 °C temperature set point beginning on 1 Apr. 2011 at both Cornell University (Ithaca, NY) and Purdue University (West Lafayette, IN). Although seven of the species exhibited a delay in flowering in the HT as compared with the heated GH, there were no differences in days to flower (DTF) for geranium, osteospermum, and viola grown at Cornell and viola at Purdue. The remaining species exhibited delays in flowering in the HT environment, which varied based on species. At Purdue, several species were lost because of a cold temperature event necessitating a second planting. For the second planting, osteospermum was the only species grown that flowered significantly later in the HT; 7 days later than the GH-grown plants. Production of cold-tolerant annuals in unheated or minimally heated HTs appears to be a viable alternative for commercial producers aiming to reduce energy costs.

Open access

Joshua K. Craver, Krishna S. Nemali, and Roberto G. Lopez

Indoor production of bedding plant seedlings using sole-source radiation may present value in increasing uniformity and consistency compared with greenhouse production. However, information on physiological acclimation related to growth and photosynthesis in seedlings exposed to high-intensity blue radiation and elevated CO2 is limited. Seedlings of petunia (Petunia ×hybrida) ‘Dreams Midnight’ were exposed to red (peak = 660 nm):blue (peak = 451 nm) radiation ratios of 50:50 (R50:B50) or 90:10 (R90:B10) and radiation intensities of 150 or 300 µmol·m−2·s–1 under two CO2 regimes of 450 or 900 µmol·mol–1. Shoot dry mass (SDM), leaf area index (LAI), internode length, and whole-plant photosynthesis and light-use efficiency (LUE) responses to increasing radiation intensity were measured. In addition, leaf photosynthetic rate (A) was measured at ambient and supra-optimal CO2 concentrations for plants grown under 450 µmol·mol–1 CO2. Our results indicated growth (based on SDM, LAI, and internode length) was lowered for seedlings produced under R50:B50 compared with R90:B10. However, we observed an increase in whole-plant light-saturated photosynthesis (Ag,max) and whole-plant light saturation point (LSP) under R50:B50 compared with R90:B10. In addition, we observed lower LUE below and higher LUE above a radiation intensity of 500 µmol·m−2·s–1 in seedlings grown under R50:B50 compared with R90:B10. Based on our results, seedling growth was lowered under a high proportion of blue radiation mainly due to lower radiation interception (due to lower LAI and shorter internode length) and LUE of intercepted radiation at the intensities used. Higher Ag,max and LSP in R50:B50 compared with R90:B10 under higher radiation intensities was likely in part due to higher LUE. Further investigation revealed A was higher at both optimal and supra-optimal CO2 concentrations under R50:B50 compared with R90:B10, indicating a lack of stomatal effects of a higher proportion of blue radiation on carboxylation and LUE. We hypothesize that higher LUE in R50:B50 compared with R90:B10 under higher radiation intensities is due to improved photochemical quenching from increased biosynthesis of carotenoids and anthocyanins. The results from our study generated fundamental information on growth and photosynthetic responses to excess blue radiation, data that can be further used in optimizing plant production in controlled environments.

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W. Garrett Owen, Alyssa Hilligoss, and Roberto G. Lopez

Production and market value of U.S. grown specialty cut flowers has increased over the past several years due to stem quality issues related to long-distance transport, regional proximity to market centers, and consumer’s willingness to purchase locally. Cut flowers are traditionally grown in field or greenhouse environments; however, high tunnels provide an alternative production environment and a number of cultural and economic advantages. Specialty cut flower species ‘Campana Deep Blue’ bellflower (Campanula carpatica), bells of ireland (Moluccella laevis), ‘Bombay Firosa’ celosia (Celosia cristata), ‘Amazon Neon Purple’ dianthus (Dianthus barbatus), ‘Fireworks’ gomphrena (Gomphrena pulchella), ‘Vegmo Snowball Extra’ matricaria (Tanacetum parthenium), and ‘Potomac Lavender’ snapdragon (Antirrhinum majus) were planted in both field and high tunnel environments during the late season (early summer) in the midwestern United States. Compared with field production, high tunnel production yielded 9.1 stems/m2 (75%) for bells of ireland and 9.5 cm (15%), 16.8 cm (16%), 6.7 cm (44%), and 6.3 cm (19%) longer stems for bells of ireland, celosia, gomphrena, and matricaria, respectively. Additionally, stem length and caliper was greatest for high tunnel–grown bells of ireland, celosia, and dianthus. Our results indicate that late-season planting and production in a high tunnel is suitable for most of the species we investigated.

Free access

A. Michel-Rosales, J. Farias, S. Guzman, G. Lopez, and G. Valdovinos

In western Mexico, banana is traditionally multiplied by vegetative reproduction in the orchard; recently, micropropagation of this species has increased considerably. Banana has been shown to give a positive response to AM fungal inoculation. However, the selection of efficient AM fungi species, currently propagated in vitro, has not been documented. The selection of the most-effective arbuscular mycorrhizal (AM) fungi for growth enhancement of banana vitroplants is the first step toward development of an AM inoculation system. This work reports the effect of nursery inoculation of Glomus aggregatum, G. clarum, G. etunicatum, G. intraradices, G. monosporum, G. mosseae, and Gigaspora margarita on the banana vitroplants growth. Pots (4 kg) containing a mixture of soil and coconut fiber (1:1) sterilized with methyl bromide were used. Treatments were arranged under a fully randomized experimental design with eight replications. The plants were harvested 120 days after inoculation and plant height, number of leaves, leaf area, fresh weight of roots, mycorrhizal colonization, and intensity of infection were measured. Glomus etunicatum, G. monosporum, G. mosseae, and G. aggregatum were shown to be the most-effective endophytes. Plant height was increased, as well as the production of banana roots in response to mycorrhizal inoculation with these fungi. On the other hand, G. intraradices and G. clarum showed low levels of colonization. The data clearly show the most efficient AM fungi for future inoculation studies in nursery banana production.

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J. Farias Larios, J. G. López Aguirre, E. Rincón Cruz, and F. Radillo Juarez

Since 1980, farmers from western Mexico have cultivated melon cantaloupe; however, during the past few years, they have seen the better advantages of honeydew melon. Some of them represent a good alternative to farmers because chemical products and labor costs are reduced, and because they are tolerant to several diseases. The purpose of this experiment was to evaluate 15 new hybrids of honeydew melon in western Mexico. The hybrids evaluated were: Dey Break, Hmx 4596, Hmx 4595, Hmx 4607, Sunex 7051, Rocio, creme de menthe, Silver world, Emerald sweet, Sme 5303, Sme 5302, Santa Fé, PSR 10994, and PSR 8994, Honey Brew was test. Fifteen -day-old plants were transplanted by hand. Treatments were replicated four times in a randomized complete-block design. Beds 1.2 m wide and 7.0 m long were prepared, 1.5 m between beds, distance plant-plant 0.5 m (plant density ≈13,332 plant/ha). Results show that yield of SME 5302, SME 5303, HMX 4596, Rocío, Dey Break, PSR 8994, Sunex 7051, and HMX 4607 had a yield higher of 50 t/ha, Emerad sweet had more number fruit (59 per 10 plants), whereas SME 5303, SME 5302 and Silver world had higher fruit weight (>1.719 gr). We suggest the evaluation of these hybrids in other regions to know the adaptation to different conditions and to select the best in commercial quality and production.

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Tanya J. Hall, Roberto G. Lopez, Maria I. Marshall, and Jennifer H. Dennis

In recent years, the commercial greenhouse industry has begun to implement sustainable production practices. However, floriculture certification programs for sustainable production practices are a relatively new phenomenon in the United States. Between July and Oct. 2008, a commercial floriculture grower survey was conducted to determine potential barriers to sustainable floriculture certification. Using a logistic regression model, seven potential areas were evaluated: risk, profitability, economic viability, prior experience, education, operation size, and customer types. Although respondents had positive attitudes toward sustainability and had adopted sustainable practices, respondents had little knowledge and interest in U.S. certification.

Free access

Joshua R. Gerovac, Joshua K. Craver, Jennifer K. Boldt, and Roberto G. Lopez

Multilayer vertical production systems using sole-source (SS) lighting can be used for the production of microgreens; however, traditional SS lighting methods can consume large amounts of electrical energy. Light-emitting diodes (LEDs) offer many advantages over conventional light sources, including high photoelectric conversion efficiencies, narrowband spectral light quality (LQ), low thermal output, and adjustable light intensities (LIs). The objective of this study was to quantify the effects of SS LEDs of different light qualities and intensities on growth, morphology, and nutrient content of Brassica microgreens. Purple kohlrabi (Brassica oleracea L. var. gongylodes L.), mizuna (Brassica rapa L. var. japonica), and mustard [Brassica juncea (L.) Czern. ‘Garnet Giant’] were grown in hydroponic tray systems placed on multilayer shelves in a walk-in growth chamber. A daily light integral (DLI) of 6, 12, or 18 mol·m−2·d−1 was achieved from commercially available SS LED arrays with light ratios (%) of red:green:blue 74:18:8 (R74:G18:B8), red:blue 87:13 (R87:B13), or red:far-red:blue 84:7:9 (R84:FR7:B9) with a total photon flux (TPF) from 400 to 800 nm of 105, 210, or 315 µmol·m−2·s−1 for 16 hours. Regardless of LQ, as the LI increased from 105 to 315 µmol·m−2·s−1, hypocotyl length (HL) decreased and percent dry weight (DW) increased for kohlrabi, mizuna, and mustard microgreens. With increasing LI, leaf area (LA) of kohlrabi generally decreased and relative chlorophyll content (RCC) increased. In addition, nutrient content increased under low LIs regardless of LQ. The results from this study can help growers to select LIs and LQs from commercially available SS LEDs to achieve preferred growth characteristics of Brassica microgreens.