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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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S. Guzman, H. Alejandro, J. Farias, A. Michel, and G. Lopez

Watermelon (Citrullus vulgaris Schrad.) is a widely grown crop throughout the tropics and subtropics. In Mexico, it is an economically important crop. In vitro adventitious shoot regeneration of watermelon has been reported from shoot tip culture, leaf, hypocotyl, and cotyledons. Hence, the objective of this study was to evaluate in vitro plant regeneration from axillary buds of triploid watermelon. Axillary buds explants were prepared from shoot of commercial cultivar in field of 60 old day plants. Explants of 2 to 3 mm were incubated 2 weeks on Murashige and Skoog (MS) shoot regeneration medium containing 2.5 mg/L kinetin (KT) or indole-3-butyric acid (IBA), or gibberellic acid (GA3), followed by 3 weeks on shoot elongation medium supplemented with different combinations of the same phytohormones. The percentage of explants (83% to 90%) that produced shoots, expansion in size of explant (0.81–1 cm) and shoot length (6 mm) were highest in MS medium containing KT or IBA. In the shoot elongation step, shoot length (0.9–1 cm) and leaves number (6–7) were highest in MS medium supplemented with 2.5 mg/L of KT or GA3 and 0.2 mg/L IBA, but the better induction of roots in elongated shoot occurred on MS medium with 2.5 mg/L KT and 0.2 mg/L IBA. The results show that axillary buds from watermelon is an alternative for the micropropagation of this crop.

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

Vegetatively propagated bedding plants are produced during the late winter and early spring when outdoor photosynthetic daily light integral (DLI) is low, especially in northern latitudes. Our objective was to quantify how propagation DLI influences subsequent growth and development of annual bedding plants. Cuttings of Angelonia angustifolia Benth. ‘AngelMist White Cloud’, Nemesia fruticans (Thunb.) Benth. ‘Aromatica Royal’, Osteospermum ecklonis (DC.) Norl. ‘Voltage Yellow’, and Verbena ×hybrida Ruiz ‘Aztec Violet’ were harvested and propagated in a glass-glazed greenhouse. After callusing (≈5 mol·m−2·d−1 for 7 days), cuttings of each species were placed under one of three different fixed-woven shadecloths providing ≈38%, 61%, or 86% shade or no shade with 16 h of supplemental light for 14 days. Rooted cuttings were then transplanted into 11-cm containers and grown in a common greenhouse of 21 ± 1 °C and DLI of ≈12 mol·m−2·d−1 to identify any residual effects on subsequent growth and development during the finish stage. As DLI during propagation increased, time to first open flower decreased for Angelonia, Nemesia, Osteospermum, and Verbena. For example, time to flower for Angelonia and Osteospermum was hastened by 23 and 19 days, respectively, as DLI during propagation increased from 1.2 to 12.3 mol·m−2·d−1. Our research can be used to predict growth and flowering under varying propagation DLIs for the cultivars of Angelonia, Nemesia, Osteospermum, and Verbena in the study.

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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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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.