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Joshua R. Gerovac, Roberto G. Lopez, and Neil S. Mattson

Commercial bedding plant production in northern latitudes often begins in late winter and continues through spring, when average outdoor temperatures require growers to actively heat their greenhouses (GHs). High tunnels (HTs) offer energy savings as they are passively heated and cooled structures that have a low initial cost. As a result, they have been used in northern latitudes to advance and extend the growing season and improve the quality of high-value horticultural crops. However, there is limited published information on growing bedding plants in HTs in northern latitudes. Our objectives were to quantify the effects of transplant date in an HT with or without a rowcover (RC) compared with a traditional heated GH on the growth and morphology of three cold-tolerant bedding plant species at two northern latitude locations, Purdue University (Purdue) and Cornell University (Cornell). Seedlings of snapdragon (Antirrhinum majus L. ‘Liberty Classic Yellow’), dianthus (Dianthus chinensis L. ‘Telstar Crimson’), and petunia (Petunia ×hybrida Vilm.-Andr. ‘Wave Pink’) were transplanted on weeks 13, 14, and 15 in 2012 (Purdue) and 2013 (both locations) and moved to either a glass-glazed GH or an HT without (HT) or with a rowcover (HT+RC). Several quality measurements increased when plants were grown in the HT compared with those grown in the GH. Dianthus and petunia transplanted at Purdue during week 13 in the HT and HT+RC were 33% and 47% shorter and had 51% and 31% more visible buds, respectively, compared with those grown in the GH. Similarly, petunia transplanted at Cornell during week 13 in the HT and HT+RC were 45% and 43% shorter, respectively, than their GH counterparts. The shoot dry mass of dianthus and snapdragon at Purdue was significantly higher when grown in the HT compared with the GH, regardless of transplant week or the use of RC likely because of increased daily light integral (DLI) in the HT environment. There was about a 1-week delay from transplant to first open flower for week 13 dianthus (at Purdue) and petunia (at both locations) when finished in the HT or HT+RC vs. their GH counterparts. Such a delay would be acceptable to growers who want to reduce the use of chemical growth regulators and heating costs. However, at both locations snapdragon transplanted on week 13 to the HT or HT+RC environments were delayed by 22 to 26 days compared with the GH. A delay of over 3 weeks could interfere with a grower’s production schedule, possibly making this crop unsuitable for production in northern latitude HTs.

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Diane M. Camberato, James J. Camberato, and Roberto G. Lopez

Chemical plant growth regulators (PGRs) are important tools in greenhouse ornamental crop production because growers must increasingly meet specifications for plant shipping and marketability. However, the role of water quality parameters such as pH or alkalinity (bicarbonate in this study) on final PGR solution pH is not well documented and could impact efficacy. We assessed the interaction of PGR type and concentration on the final spray solution pH when combined with carrier water of varying pH and bicarbonate concentration. Eleven PGRs commonly used in floriculture (ancymidol, benzyladenine, chlormequat chloride, daminozide, dikegulac-sodium, ethephon, flurprimidol, gibberellic acid, gibberellic acid/benzyladenine, paclobutrazol, and uniconazole) at three concentrations (low, medium, and high recommended rates for each product) were added to reverse osmosis (RO) carrier water adjusted to four pH (5.3, 6.2, 7.2, 8.2) levels or added to tap carrier water adjusted to four bicarbonate concentrations (40, 86, 142, 293 mg·L−1 of CaCO3). Resultant solution pH levels were measured. Plant growth regulators were categorized as acidic, neutral, or basic in reaction based on the change of the carrier water pH on their addition. Benzyladenine, chlormequat chloride, gibberellic acid, and gibberellic acid/benzyladenine acted as weak acids when added to RO water, whereas daminozide, ethephon, and uniconazole reduced final solution pH from 1.25 to 5.75 pH units. Flurprimidol and paclobutrazol were neutral in reaction with final solution pH being similar to that of the RO carrier water before their addition. Ancymidol and dikegulac-sodium were basic in reaction, increasing final solution pH in RO carrier water up to 2.3 units. There was an interaction between chlormequat chloride concentration and RO carrier water pH on change in pH. When added to tap carrier water, final solution pH increased for all except the stronger acids, daminozide, ethephon, and uniconazole, where it decreased up to 3.5 units, and benzyladenine, where it decreased 0.35 units at 40 mg·L−1 bicarbonate. There was an interaction between PGR concentration and bicarbonate concentration in tap carrier water for daminozide and ethephon. The magnitude of change in pH (final solution pH minus initial carrier water pH) with the addition of each PGR was greater for RO than for tap water containing 40 to 293 mg·L−1 bicarbonate for all 11 PGRs tested.

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Christopher J. Currey, Veronica A. Hutchinson, and Roberto G. Lopez

Cuttings of herbaceous annual bedding plants must be rooted in late winter and early spring when ambient outdoor photosynthetic daily light integrals (DLIs) are at seasonally low levels. We evaluated the effect of DLI during root development on growth, morphology, and quality of nine popular vegetatively propagated annual bedding plant species. Cuttings of Angelonia angustifolia Benth. ‘AngelMist White Cloud’, Argyranthemum frutescens (L.) Sch. Bip. ‘Madeira Cherry Red’, Diascia barberae Hook. f. ‘Wink Coral’, Lantana camara L. ‘Lucky Gold’, Nemesia fruticans (Thunb.) Benth. ‘Aromatica Royal’, Osteospermum ecklonis (DC.) Norl. ‘Voltage Yellow’, Scaevola L. hybrid ‘Blue Print’, Sutera cordata Roth. ‘Abunda Giant White’, and Verbena Ruiz ×hybrida ‘Aztec Violet’ were harvested and propagated in a glass-glazed greenhouse with 23 °C air and substrate temperature set points. After callusing (≈5 mol·m−2·d−1 for 7 days), cuttings of each species were placed under one of three different fixed-woven shade cloths providing ≈38%, 61%, or 86% shade or no shade with 16 h of supplemental light for 14 days. There were no clear trends across species for stem length in response to DLI. Stem caliper of Argyranthemum, Diascia, and Nemesia increased by 35%, 119%, and 89%, respectively, as DLI increased from 1.2 to 12.3 mol·m−2·d−1. Depending on species, total, shoot, and root dry mass increased by 64% to 465%, 50% to 384%, and 156% to 1137%, respectively, as DLI increased from 1.2 to 12.3 mol·m−2·d−1. The quality index, an objective, integrated, and quantitative measurement of rooted cutting quality, increased for all species by 176% to 858% as DLI increased from 1.2 to 12.3 mol·m−2·d−1. Our results indicate that providing a DLI of ≈8 to 12 mol·m−2·d−1 after callusing increases both growth and quality of rooted cuttings.

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Michael A. Ortiz, Krystyna Hyrczyk, and Roberto G. Lopez

The U.S. specialty cut flower market has grown over the last several years because stems of many specialty cut flower species cannot be transported long distances and therefore need to be grown regionally. High tunnel production of cut flowers is an alternative to field and greenhouse production that has several benefits. Specialty cut flower species Antirrhinum majus L. ‘Potomac Orange’ and ‘Rocket Red’, Celosia argentea L. var. cristata Kuntze ‘Chief Red’, Dahlia ×hybrida Cav. ‘Karma Thalia Dark Fuchsia’, Dianthus barbatus L. ‘Amazon Neon Cherry’, Eustoma russellianum Salisb. ‘Mariachi Blue’, Helianthus annuus L. ‘Premier Lemon’ and ‘Sunrich Yellow’, Matthiola incana (L.) W.T. Aiton ‘Katz Lavender Blue’, and Zinnia elegans Jacq. ‘Benary Giant Scarlet’ were grown in both field and high tunnel environments in the midwestern United States. High tunnel production resulted in a first week’s harvest of 44.8 (46%), 115, and 21.1 (110%) more stems for Antirrhinum ‘Rocket Red’, Dianthus, and Zinnia, respectively. Compared with field production, high tunnel production yielded a greater number of stems/m2 for Antirrhinum ‘Potomac Orange’, Celosia, Dianthus, and Zinnia and longer stems for Antirrhinum ‘Potomac Orange’ and ‘Rocket’, Eustoma, Matthiola, and Zinnia. For example, high tunnel production yielded 185 (39%) and 192 (59%) more stems/m2 and 12.6 (34%) and 8.9 (32%) cm longer stems for Mathiola and Zinnia, respectively. Other stem characteristics such as inflorescence length and flower width showed more variation among cultivars. Our results indicate that cut flower yield and/or quality of Antirrhinum ‘Rocket Red’, Dianthus, Matthiola, Zinnia, Dahlia, Eustoma, and Helianthus ‘Sunrich Yellow’ and ‘Premier Lemon’ significantly increases when produced in high tunnels located in the Midwest.

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Francisco Lopez-Gutierrez, Harrison G. Hughes, and Nicholas C. Carpita

After 6 months of growth in 200,400, and 500 mm NaCl, cultured cells of Distichlis spicata showed a decreased cell volume (size) despite maintenance of turgor pressure sometimes 2-fold higher than that of the control. Tensile strength, as measured by a nitrogen gas decompression technique, showed empirically that the walls of NaCl-stressed cells were weaker than those of nonstressed cells. Breaking pressures of the walls of control cells were ≈68 ± 4 bars, while that of the walls of cells grown in 500 mm NaCl (-25 bars) were 14 ± 2 bars. The relative amount of cellulose per cell remained about constant despite salt stress. However, glucuronoarabinoxylans were more readily extractable, presumably because of a decrease in cross-linkage with phenol substances. Therefore, we suggest that cellulose microfibrils are not the only determinants that confer tensile strength to the primary cell wall, but rather subtle changes in the matrix polysaccharides are likely responsible for this event.

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César Guzmán-Loza, J. Farías-Larios, and J.G. López-Aguirre

Use of arbuscular mycorrhizal fungi (MA) on horticultural plant production has great potential as a biotechnological alternative; however, information on its effects on the early growth phase of honeydew melon is lacking. Nevertheless, it would seem that inoculation at the time of sowing would decrease the stress of transplant, improve root vigor, make plants grow faster, improve drought resistance, and lessen the effect of roots diseases. In this study, we evaluated the effects of inoculating honeydew melon seedlings with two commercial formulations of MA fungi at different study times in an effort to select for higher resistance and infective capacity. `Moonshine' hybrid melon seeds were sown in trials with 200 cavities containing specific doses of inoculate: 0, 100, 200, 250, 500, and 1000 cc/trial of BuRIZE, Mycorrhiza NES. A factorial design was used (formulations and study times) with a randomized distribution and four replications. Four destructive samples were taken at 10, 15, 20, and 25 days after inoculations. Number of leaves, shoot fresh weight, dry weight, root fresh weight, foliar area, and mycorrhizal colonization were recorded. Results obtained showed a highly significant effect between commercial formulations and study times and an interaction of both factors to studied variables. Mycorrhizal colonization percentages were too low (0.3% to 1.7%). At 20 days after inoculations, it was possible to see all the components of functional arbuscular mycorrhizal symbiosis on melon plants roots. Using commercial formulations of mycorrhizal fungi decreased applications of fertilizers in melon plants.

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Ariana P. Torres, Michael V. Mickelbart, and Roberto G. Lopez

Well-established protocols exist for using the pour-through extraction method to estimate substrate pH and electrical conductivity (EC) values for small root volumes. However, little work has been done to test the accuracy and consistency of these measurements in large containers. Our objective was to determine if the amount of distilled water applied to #1, #3, #5, and #10 (2-, 8-, 11-, and 27-L media volume, respectively) containers would affect leachate pH and EC values or consistency of measurements. Boxwood (Buxus ×koreana ‘Green Velvet’) was selected for this study because it is a common container-grown nursery crop. Distilled water was poured evenly over the media surface in each container 1 h after irrigation to obtain a leachate volume of either 50 mL or 2.5% of media volume and leachate EC and pH were measured. Media pH values were 0.1 to 0.3 points higher when 50 mL leachate was collected, but the difference was only significant during the first 2 weeks of measurements. There were no consistent differences in pH over container sizes or leachate volume. Leachate EC values were similar when measured in leachate collected as 50 mL total volume or 2.5% of media volume in 8- and 11-L containers. However, in 27-L containers, obtaining 50 mL leachate resulted in higher EC values than when 2.5% media volume was obtained. Both pH and EC values obtained from 50-mL leachate fractions over container sizes were more consistent than when 2.5% of the media volume was collected. Growers should collect 50 mL of leachate to test media pH and EC regardless of container size.

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Diane M. Camberato, James J. Camberato, and Roberto G. Lopez

Four complete water-soluble fertilizer (WSF) formulations including micronutrients applied at 200 mg·L−1 nitrogen (N) at each irrigation [Peters Excel (21N–2.2P–16.5K), Daniels (10N–1.8P–2.5K), Peters Professional (15N–1.3P–20.8K), and Jack’s Professional (20N–1.3P–15.7K)] were compared with two controlled-release fertilizer (CRF) products (also containing micronutrients) substrate incorporated at transplant at a rate of 3000 g·m−3 of substrate [Osmocote Plus (15N–4P–9.9K, 90 to 120 days longevity at 21 °C) and Osmocote Bloom (12N–3.1P–15K, 60 to 90 days longevity at 21 °C)] in the greenhouse production of four commonly produced bedding plant species with high alkalinity irrigation water (pH 7.1, 280 mg·L−1 CaCO3 equivalent). Species included Argyranthemum frutescens (L.) Sch. Bip. ‘Madeira Cherry Red’ and iron-inefficient Calibrachoa Cerv. hybrid ‘Cabaret Pink Hot’, Diascia barberae Hook. f. ‘Wink Coral’, and Sutera cordata Roth ‘Abunda Giant White’. Additional treatments included a combination of 100 mg·L−1 Excel and 2100 g·m−3 Osmocote Plus and an Osmocote Plus treatment irrigated with reduced alkalinity water (acidified to pH 6.3, 92 mg·L−1 CaCO3 equivalent). Bedding plants were evaluated at the end of a finish or market stage (3 or 5 weeks depending on species) for shoot dry mass (SDM) and root dry mass (RDM), tissue nutrient concentrations, and visual quality rating (0 to 4). At 3 weeks, there were no significant differences in SDM and RDM between fertilizer treatments for any of the four species. Shoot dry mass significantly increased at 5 weeks in the WSF and combination treatments over the three CRF only treatments for Argyranthemum and over the non-acidified Osmocote Plus treatment only for Calibrachoa. At finish, 3 weeks for Sutera and Diascia and 5 weeks for Argyranthemum and Calibrachoa, visual quality rating for all species was lowest when using Osmocote Plus with or without acidified irrigation water compared with the WSF treatments, except the Daniels treatment in Argyranthemum, which also resulted in a low visual quality rating. Leaf tissue N for all species and phosphorus (P) for all except Diascia were below the recommended range for bedding plant crops in the CRF treatments, which was reflected by the lower substrate electrical conductivity (EC) for the CRF alone and combination treatments. Leaf tissue N and P were related to visual quality rating for all species, leaf tissue potassium (K) for Argyranthemum and Calibrachoa only, and leaf tissue iron (Fe) for Diascia only.

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

Previous research has shown high-quality annual bedding plant seedlings can be produced in controlled environments using light-emitting diode (LED) sole-source lighting (SSL). However, when only red and blue radiation are used, a delay in time to flower may be present when seedlings of some long-day species are subsequently finished in a greenhouse. Thus, our objective was to evaluate the effects of various radiation qualities and intensities under SSL on the morphology, nutrient uptake, and subsequent flowering of annual bedding plant seedlings with a long-day photoperiodic response. Coreopsis (Coreopsis grandiflora ‘Sunfire’), pansy (Viola ×wittrockiana ‘Matrix Yellow’), and petunia (Petunia ×hybrida ‘Purple Wave’) seedlings were grown at radiation intensities of 105, 210, or 315 µmol·m−2·s−1, achieved from LED arrays with radiation ratios (%) of red:blue 87:13 (R87:B13), red:far-red:blue 84:7:9 (R84:FR7:B9), or red:green:blue 74:18:8 (R74:G18:B8). Four-week-old seedlings were subsequently transplanted and grown in a common greenhouse environment. Stem caliper, root dry mass, and shoot dry mass of seedlings generally increased for all three species as the radiation intensity increased from 105 to 315 µmol·m−2·s−1, regardless of radiation quality. Similarly, stem length of all three species was generally shorter as the radiation intensity increased. Macro- and micronutrient concentrations were also generally lower as the radiation intensity increased for all three species. Pansy seedlings grown under R84:FR7:B9 flowered an average of 7 and 5 days earlier than those under R87:B13 and R74:G18:B8, respectively. These results provide information regarding the specific radiation parameters from commercially available LEDs necessary to produce high-quality seedlings under SSL, with radiation intensity appearing to be the dominant factor in determining seedling quality. Furthermore, the addition of far-red radiation can reduce time to flower after transplant and allow for a faster greenhouse turnover of some species with a long-day photoperiodic response.

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

High-quality young plant production in northern latitudes requires supplemental lighting (SL) to achieve a recommended daily light integral (DLI) of 10 to 12 mol·m−2·d−1. High-pressure sodium (HPS) lamps have been the industry standard for providing SL in greenhouses. However, high-intensity light-emitting diode (LED) fixtures providing blue, white, red, and/or far-red radiation have recently emerged as a possible alternative to HPS lamps for greenhouse SL. Therefore, the objectives of this study were to 1) quantify the morphology and nutrient concentration of common and specialty bedding plant seedlings grown under no SL, or SL from HPS lamps or LED fixtures; and 2) determine whether SL source during propagation or finishing influences finished plant quality or flowering. The experiment was conducted at a commercial greenhouse in West Lafayette, IN. Seeds of New Guinea impatiens (Impatiens hawkeri ‘Divine Blue Pearl’), French marigold (Tagetes patula ‘Bonanza Deep Orange’), gerbera (Gerbera jamesonii ‘Terracotta’), petunia (Petunia ×hybrida ‘Single Dreams White’), ornamental millet (Pennisetum glaucum ‘Jester’), pepper (Capsicum annuum ‘Hot Long Red Thin Cayenne’), and zinnia (Zinnia elegans ‘Zahara Fire’) were sown in 128-cell trays. On germination, trays were placed in a double-poly greenhouse under a 16-hour photoperiod of ambient solar radiation and photoperiodic lighting from compact fluorescent lamps providing a photosynthetic photon flux density (PPFD) of 2 µmol·m−2·s−1 (ambient conditions) or SL from either HPS lamps or LED fixtures providing a PPFD of 70 µmol·m−2·s−1. After propagation, seedlings were transplanted and finished under SL provided by the same HPS lamps or LED fixtures in a separate greenhouse environment. Overall, seedlings produced under SL were of greater quality [larger stem caliper, increased number of nodes, lower leaf area ratio (LAR), and greater dry mass accumulation] than those produced under no SL. However, seedlings produced under HPS or LED SL were comparable in quality. Although nutrient concentrations were greatest under ambient conditions, select macro- and micronutrient concentrations also were greater under HPS compared with LED SL. SL source during propagation and finishing had little effect on flowering and finished plant quality. Although these results indicate little difference in plant quality based on SL source, they further confirm the benefits gained from using SL for bedding plant production. In addition, with both SL sources producing a similar finished product, growers can prioritize other factors related to SL installations such as energy savings, fixture price, and fixture lifespan.