Supplemental lighting is required for the production of high-quality vegetable transplants in greenhouses when the photosynthetic daily light integral (DLI) is low. Light-emitting diodes (LEDs) are a promising alternative to high-pressure sodium (HPS) lamps. However, there are a limited number of studies that have evaluated how LED supplemental lighting spectral quality beyond blue (B) and red (R) radiation influences plant growth and development. Seeds of hybrid greenhouse seedless cucumber ‘Elsie’ (Cucumis sativus), tomato ‘Climstar’ (Solanum lycopersicum), and pepper ‘Kathia’ (Capsicum annuum) were sown and placed into a dark growth chamber until radicle emergence. Seedlings were grown in a greenhouse at a 25 °C constant temperature set point and under five lighting treatments. The supplemental lighting treatments delivered a total photon flux density (TPFD) of 120 μmol·m−2·s−1 for 16 h·d−1 based on an instantaneous threshold from HPS lamps or LEDs [three treatments composed of B (400–500 nm), R (600–700 nm), white, and/or far-red (FR; 700–800 nm) LEDs], and a control that delivered 25 μmol·m−2·s−1 from HPS lamps (HPS25). The LED treatments defined by their wavebands (TPFD in μmol·m−2·s–1) of B, green (G, 500–600 nm), R, and FR radiation were B20G10R75FR15, B25R95, and B30G30R60; whereas the HPS treatments emitted B7G57R47FR9 (HPS120) and B1G13R9FR2 (HPS25). Generally, cucumber, pepper, and tomato transplants under B30G30R60 and HPS120 supplemental lighting had the greatest stem diameter. Fresh weight and leaf area of all three species was greater when G radiation replaced R or B radiation. For example, leaf area and fresh weight of cucumber, tomato, and pepper increased (by 33%, 22%, and 49%; and 35%, 14%, and 56%, respectively) for plants under B30G30R60 supplemental lighting compared with plants under B25R95 supplemental lighting. The most compact cucumber and pepper transplants were those grown under B25R95 supplemental lighting, and the most compact tomatoes were those grown under the HPS25 (control) and B25R95 supplemental lighting. Tomato transplants under treatments providing ≥30 μmol·m−2·s−1 of G radiation had an increased incidence of leaf necrosis. From this study, we conclude that plant responses to supplemental lighting quality are generally genera-specific, and therefore high-wire transplants should be separated by genera to optimize production and quality. However, additional studies are required to provide complete LED supplemental lighting recommendations.
Charlie Garcia and Roberto G. Lopez
Roberto G. Lopez and Erik S. Runkle
The vegetatively propagated `Fire Kiss' clone of the hybrid Zygopetalum Redvale orchid has appealing potted-plant characteristics, including fragrant flowers that are waxy lime-green and dark maroon with a broad, three-lobed, magenta and white labellum. We performed experiments to quantify how temperature influenced leaf unfolding and expansion, time from visible inflorescence to flower, and longevity of individual flowers and inflorescences. Plants were grown in controlled-environment chambers with constant temperature set points of 14, 17, 20, 23, 26, and 29 °C and an irradiance of 150 μmol·m-2·s-1 for 9 h·d-1. As actual temperature increased from 14 to 25 °C, the time to produce one leaf decreased from 46 to 19 days. Individual plants were also transferred from a greenhouse to the chambers on the date that an inflorescence was first visible or the first flower of an inflorescence opened. Time from visible inflorescence to open flower decreased from 73 days at 14 °C to 30 days at 26 °C. As temperature increased from 14 to 29 °C, flower and inflorescence longevity decreased from 37 and 38 days to 13 and 15 days, respectively. Data were converted to rates, and thermal time models were developed to predict time to flower and senescence at different temperatures. The base temperature was estimated at 6.2 °C for leaf unfolding, 3.5 °C for time to flower, and 3.7 °C for flower longevity. These models could be used by greenhouse growers to more accurately schedule Zygopetalum flowering crops for particular market dates.
Roberto G. Lopez and Erik S. Runkle
Prohexadione-Ca (ProCa) is a relatively new plant growth regulator (PGR) that inhibits internode length in rice, small grains, and fruit trees. However, little is known about its efficacy and potential phytotoxicity on floriculture crops and how it compares to other commercially available PGR chemicals. The effects of two foliar spray applications (2 weeks apart) of ProCa (500, 1000, or 2000 ppm), paclobutrazol (30 ppm), or a tank mix of daminozide plus chlormequat (2500 and 1000 ppm, respectively) were quantified on Dianthus barbatus L. `Interspecific Dynasty Red', Ageratina altissima R. King & H. Robinson (Eupatorium rugosum) `Chocolate', Lilium longiflorum Thunb. `Fangio', and Buddleia davidii Franch. `Mixed.' All plants were forced in a glass-glazed greenhouse with a constant temperature setpoint of 20 °C under a 16-h photoperiod. Two weeks after the second spray application of ProCa at 500, 1000, or 2000 ppm, plant height of Dianthus and Lilium was shorter than control plants by 56%, 60%, and 65% and by 6%, 26%, and 28%, respectively. However, ProCa bleached and reduced the size of Dianthus flowers. ProCa at 2000 ppm and daminozide plus chlormequat were effective at controlling the height of Eupatorium (64% and 53% reduction, respectively); however, leaves of Eupatorium were discolored and showed symptoms of phytotoxicity 1 week after the first ProCa application. Only daminozide plus chlormequat were effective on Buddleia. ProCa is an effective PGR for most of the crops we tested; however, its discoloration of red flowers and foliage may limit its application for commercial use.
Roberto G. Lopez and Erik S. Runkle
In 2003, commercial greenhouse growers in the United States imported 724 million nonrooted cuttings valued at $53 million. During transit and storage, cuttings can be exposed to environmental stresses (e.g., low or high temperature), which can consequently decrease quality, rooting, and subsequent plant performance. We performed experiments to quantify how temperature and storage duration of cuttings influence root initiation, root number, lateral branch count and length, and time to flower of Tiny Tunia `Violet Ice' petunia (Petunia × hybrida hort. Vilm. -Andr.). Dry or wet cuttings were harvested and packaged into perforated bags within small, ventilated boxes and then into traditional shipping boxes. The boxes were placed in environmental chambers with temperature setpoints of 0, 5, 10, 15, 20, 25, or 30 °C for 0, 1, 2, 3, 4, or 5 d. Cuttings were then rooted in a propagation house at 26 °C with a vapor pressure deficit of 0.3 kPa under ambient photo-periods. The visual quality rating of dry packaged cuttings decreased with increasing temperature and shipping duration. After 2 d at ≥25 °C, cuttings were horticulturally unacceptable due to water stress and chlorophyll degradation and they never fully recovered. Dry- or wet-packaged cuttings held at temperatures of 0 to 30 °C formed significantly fewer roots and lateral branches as duration increased from 1–5 d. Although cuttings held for 5 d at 0 °C produced 60% fewer lateral branches, they subsequently flowered 5 d earlier than plants held at 0 °C for 1 d. Therefore, exposure to temperatures >15 °C for ≥3 d can reduce petunia cutting quality, delay rooting, and decrease plant size at flowering.
Ariana P. Torres and Roberto G. Lopez
Current market trends indicate an increasing demand for unique and exotic flowering crops, including tropical plants. Tecoma stans (L. Juss. Kunth) ‘Mayan Gold’ is a tropical plant that was selected as a potential new greenhouse crop for its physical appearance and drought and heat tolerance. However, in winter and early spring, when propagation occurs, outdoor photosynthetic daily light integral (DLI) can be relatively low. The objective of this study was to quantify the effects of DLI during propagation of Tecoma and to determine optimum DLI levels for seed propagation. Seeds were propagated under 13 mean DLIs ranging from 0.75 to 25.2 mol·m−2·d−1 created by the combination of high-pressure sodium lamps (HPS) and fixed woven shadecloths of varying densities. Thirty-five days after sowing, height, stem diameter, node number, relative leaf chlorophyll content, leaf fresh weight, leaf number, total leaf area, individual leaf area, leaf area ratio, shoot and root dry mass increased as DLI increased. Average internode elongation and specific leaf area decreased at a quadratic and linear rate, respectively, as DLI increased from 0.75 to 25.2 mol·m−2·d−1. These experiments indicate that high-quality Tecoma seedlings were obtained when DLI was 14 to 16 mol·m−2·d−1 during propagation.
Roberto G. Lopez and Erik S. Runkle
Flowering potted orchids has become one of the largest segments of floriculture worldwide. Large-scale production of cuts or potted plants exists in China, Germany, Japan, The Netherlands, Taiwan, Thailand, and the United States. Despite the value of orchids, the flowering physiology of most orchid genera is not well described. Therefore, scheduling flowering crops for specific market dates (such as Easter or Mother's Day) is not possible for most genera. This paper summarizes world orchid production and reviews how environmental factors regulate growth and flowering of several commercially important orchid genera: Cattleya, Cymbidium, Dendrobium, Miltoniopsis, Phalaenopsis, and Zygopetalum. These genera primarily flower in response to relatively low temperatures, and, for some species and hybrids, flowering is promoted when the plants are also exposed to short photoperiods. Effects of light and temperature on growth and development are summarized for these genera, and implications for controlled production are discussed.
Roberto G. Lopez and Diane M. Camberato
Biodegradable, compostable, and traditional plastic containers were evaluated for production of ‘Eckespoint Classic Red’ poinsettia (Euphorbia pulcherrima), a long-term greenhouse crop (12–16 weeks transplant to finish, depending on cultivar). Containers were rated for appearance and durability during the 14-week production period and plant quality parameters were measured at anthesis. Plastic, rice hull, wheat starch-derived bioresin, and molded fiber containers remained unchanged in appearance and integrity and received a rating of 5 (1–5 rating scale, where 1 = container integrity compromised substantially and 5 = container was intact, no visible changes in terms of color or construction). However, straw, coconut coir, composted cow manure, and Canadian sphagnum moss and wood pulp containers had an average rating of 2.9, 2.7, 1.4, and 1.6, respectively. Both shoot and root dry weights were greatest in plants produced in molded fiber and straw containers. The root to shoot dry weight ratio and days to anthesis was not significantly different among container types. Bract area index (a measurement derived to estimate bract area) was greatest for plants produced in molded fiber containers and lowest for those produced in the wheat starch containers. When adjusted for container height, final plant height was greatest in molded fiber containers and lowest in wheat starch containers. Plants produced in molded fiber containers, on average, exhibited the greatest height, bract area index, and total root and shoot weight, with no visible changes to container integrity. Based on these results, plant quality was not negatively impacted by any of the seven containers, though marketability of finished plants can be affected by container integrity.
Wesley C. Randall and Roberto G. Lopez
To produce uniform, compact, and high-quality annual bedding plant seedlings in late winter through early spring, growers in northern latitudes must use supplemental lighting (SL) to achieve a photosynthetic daily light integral (DLI) of 10 to 12 mol·m−2·d−1. Alternatively, new lighting technologies may be used for sole-source photosynthetic lighting (SSL) to grow seedlings in an indoor high-density multilayer controlled environment. The objective of this study was to compare seedlings grown under low greenhouse ambient light (AL) to those grown under SL or SSL with a similar DLI. On hypocotyl emergence, seedlings of vinca (Catharanthus roseus), impatiens (Impatiens walleriana), geranium (Pelargonium ×hortorum), petunia (Petunia ×hybrida), and French marigold (Tagetes patula) were placed in a greenhouse under AL or AL plus SL delivering a photosynthetic photon flux (PPF) of 70 µmol·m−2·s–1 for 16 hours, or under multilayer SSL delivering a PPF of 185 µmol·m−2·s–1 for 16 hours in a walk-in growth chamber. Supplemental lighting consisted of high-pressure sodium (HPS) lamps or high-intensity light-emitting diode (LED) arrays with a red:blue light ratio (400–700 nm; %) of 87:13, and SSL consisted of LED arrays providing a red:blue light ratio (%) of 87:13 or 70:30. Root and shoot dry mass, stem diameter, relative chlorophyll content, and the quality index (a quantitative measurement of quality) of most species were generally greater under SSL and SL than under AL. In addition, height of geranium, petunia, and marigold was 5% to 26%, 62% to 79%, and 7% to 19% shorter, respectively, for seedlings grown under SSL compared with those under AL and SL. With the exception of impatiens, time to flower was similar or hastened for all species grown under SL or SSL compared with AL. Seedlings grown under SSL were of similar or greater quality compared with those under SL; indicating that LED SSL could be used as an alternative to traditional greenhouse seedling production.
Ariana P. Torres and Roberto G. Lopez
Tecoma stans (L. Juss. Kunth) ‘Mayan Gold’ is a tropical flowering plant that was selected as a potential new greenhouse crop for its physical appearance and drought and heat tolerance. The objective of this study was to quantify how temperature during the finishing stage and photoperiod during propagation and finishing stages influence growth, flowering, and quality. In Expt. 1, plants were propagated from seed under four photoperiods (9, 12, 14, or 16 h) for 35 days. Under long-day (LD) photoperiods (14 h or greater), seedlings were 3.0 to 3.7 cm taller than those propagated under 9-h photoperiods. During the finishing stage, days to first open flower, shoot dry mass, and number of nodes below the terminal inflorescence were reduced when plants were grown under LD photoperiods. In addition, number of open flowers and branches increased under LD photoperiods. Few plants developed visible buds when grown under short-day (SD) photoperiods (12 h or less). In Expt. 2, plants were forced at average daily temperatures of 19, 20, or 22 °C after transplant. Time to first open flower was reduced by 7 days as temperature increased. Inversely, number of visible buds increased by 57 as temperature increased from 19 to 22 °C. Under the experimental conditions tested, the most rapid, complete, and uniform flowering of Tecoma occurred when plants were propagated and finished under LD photoperiods and forced at 22 °C.
Christopher J. Currey and Roberto G. Lopez
Our objectives were to quantify the effects of controlled-release fertilizer (CRF) on the growth, morphology, and tissue nutrient concentration of annual bedding plants during propagation. Unrooted cuttings of Angelonia angustifolia ‘AngelFace White’ and ‘Sundancer Pink’, Impatiens hawkeri ‘Celebrette Apricot’ and ‘Celebrette Rose Hot’, Nemesia fruticans ‘Bluebird’ and ‘Raspberry Sachet’, Pelargonium ×hortorum ‘Savannah Red’, and Petunia ×hybrida ‘Cascadia Marshmallow Pink’ and ‘Suncatcher Yellow’ were received from a commercial propagator. Cuttings were immediately stuck individually in cells containing soilless substrate supplemented with 0, 3, 6, 12, or 24 g·L−1 CRF (Osmocote Plus 15–3.9–10 3–4 month) and placed under clear mist water or cuttings were stuck in substrate containing no CRF and fertilized with water-soluble fertilizer beginning immediately after placing cuttings into propagation. Shoot dry mass of cuttings grown in substrates containing up to 12 or 24 g·L−1 CRF increased by up to 150% for some taxa compared with unfertilized cuttings. Incorporating CRFs into propagation substrates increased the concentration of nitrogen (N), phosphorus (P), and potassium (K) in tissues by up to 103%, 42%, and 137%, respectively, compared with unfertilized cuttings. Additionally, tissue nutrient concentrations for cuttings fertilized with 6 g·L−1 CRF or greater were similar to cuttings receiving water-soluble fertilizer (WSF). When the impact of CRF on growth and nutrient concentrations are taken together, our results indicate that CRF is a fertilization application technology that holds promise for use during propagation of herbaceous stem-tip cuttings.