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Annual bedding plant seedlings or plugs are considered high quality when they are compact, fully rooted transplants with a large stem caliper and high root dry mass. Greenhouses in northern latitudes rely on supplemental lighting (SL) from high-pressure sodium lamps (HPS) during winter months to achieve high-quality, finished plugs. Light-emitting diodes (LEDs) offer higher energy efficiencies, a long operating life, and precise waveband specificity that can eliminate wavebands not considered useful. Seedlings of Antirrhinum, Catharanthus, Celosia, Impatiens, Pelargonium, Petunia, Tagetes, Salvia, and Viola were grown at 21 °C under a 16-hour photoperiod of ambient solar light and SL of 100 μmol·m−2·s–1 from either HPS lamps or LED arrays with varying proportions (%) of red:blue light (100:0, 85:15, or 70:30). Height of Catharanthus, Celosia, Impatiens, Petunia, Tagetes, Salvia, and Viola was 31%, 29%, 31%, 55%, 20%, 9%, and 35% shorter, respectively, for seedlings grown under the 85:15 red:blue LEDs compared with those grown under HPS lamps. Additionally, stem caliper of Antirrhinum, Pelargonium, and Tagetes was 16%, 8%, and 13% larger, respectively, for seedlings grown under the 85:15 red:blue LEDs compared with seedlings grown under HPS lamps. The quality index (QI), a quantitative measurement of quality, was similar for Antirrhinum, Catharanthus, Impatiens, Pelargonium, and Tagetes grown under LEDs and HPS lamps. However, it was significantly higher for Petunia, Salvia, and Viola under 85:15, 70:30, and 100:0 red:blue LEDs than under HPS lamps, respectively. These results indicate that seedling quality for the majority of the species tested under SL from LEDs providing both red and blue light was similar or higher than those grown under HPS lamps.

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Development of new strawberry cultivars for winter fruit production in Florida entails growing of hybrid seedlings in a nursery in the summer of the first year for runner plant production. Two runner plants are taken from each seedling and planted in the fruiting field in the fall. An experiment was conducted to see if it is possible to predict which genotypes in the nursery will have the highest early season fruit yield. Seedlings from 24 families from a 6 × 4 factorial mating design were grown in a nursery. From each family, daughter plants of 20 seedlings with the highest vigor and 20 randomly picked seedlings were then evaluated in the fruiting field. Plants from selected (high-vigor) seedlings were more vigorous, but had fewer crowns and runners, than unselected plants. More inflorescences were counted in selected plants than in unselected plants during the second week of January. This could account for higher early yield (yield at the end of January) and total yield (yield at the end of March) in selected than in unselected plants.

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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.

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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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The disease incited by Pepino mosaic virus (PepMV) is currently a serious problem for tomato (Solanum lycopersicum L.) crops in several European countries. A collection of accessions from different Solanum species was screened to find sources of resistance to PepMV. All plants of S. lycopersicum, S. lycopersicum var. cerasiforme, S. pennellii Correll, S. cheesmaniae (L. Riley) Fosberg, S. habrochaites S. Knapp & D.M. Spooner, S. neorickii D.M. Spooner, G.J. Anderson & R.K. Jansen, S. pimpinellifolium L., S. basendopogon Bitter, S. canense Rydb., S. caripense Humb. & Bonpl. ex Dunal, and S. muricatum Aiton accessions showed a 100% systemic infection rate, high viral accumulation, and apparent symptoms. In some accessions of the species S. chilense (Dunal) Reiche and S. peruvianum L., a variable percentage of plants without systemic infection was observed. Although all plants of ECU-335 accession of S. ochranthum Dunal showed systemic infection by PepMV, the symptoms were mild and the levels of viral accumulation were low. PepMV was not detected in plants of AN-CA-214 accession of S. pseudocapsicum L. No symptoms were observed either on inoculated leaves or on growing leaves. The use of the latter two species is limited considering that they cannot be sexually crossed with cultivated tomato. As a result, S. chilense and S. peruvianum are the most promising species in the search for sources of resistance to PepMV.

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To induce somatic embryogenesis in habanero pepper (Capsicum chinense Jacq.), the cultivar BVll-03, belonging to the red type, was used. Different explants were evaluated, as were different culture media, the composition of which varied in the content of plant growth regulators. Results showed the formation of somatic embryos from cotyledons, zygotic embryos, germinated zygotic embryos, hypocotyls, and cotyledonary leaves. Explants were cultured on Murashige and Skoog medium supplemented with 2,4-D (9.05 μm). The somatic embryos always formed directly from the explant, without callus formation, and the greatest efficiency was obtained when segments of hypocotyls were cultured, obtaining 175 ± 20 somatic embryos per explant. Only the somatic embryos obtained on Murashige and Skoog medium containing 2,4-D (9.05 μm) and treated with abscisic acid (ABA) (1.89 μm) before their transfer to the germination media (Murashige and Skoog + 1.1 μm GA3) emitted their radicule and expanded their cotyledonary leaves (60%), whereas the remaining embryos did not achieve germination because of different causes (abnormalities, delayed development). Not only is this protocol of somatic embryogenesis the first to be reported for this species (C. chinense Jacq.), but it is also the most efficient reported so far, within the Capsicum genus.

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The in vitro production of ethylene and its effects on the development of Habanero pepper (Capsicum chinense Jacq.) plantlets were evaluated using nonventilated containers (NVCs) and ventilated containers (VCs). Shoots of Habanero pepper between 0.5 and 1.0 cm of height were cultivated in Magenta culture boxes and samples of the headspace atmosphere were taken every four days during the previously established culturing time of 40 days. The presence of ethylene was detected in the NVCs and produced a negative effect on the development of plantlets. In a second phase of this work, the effect of silver nitrate (AgNO3) and cobalt chloride (CoCl2) on ethylene production was evaluated during in vitro development of Habanero pepper plantlets. Concentrations of 50, 300, and 500 μm of each ethylene inhibitor were used in the culture medium. Although cobalt chloride partially inhibited the production of ethylene during in vitro culture of this species, at low concentrations the plantlets presented some degree of vitrification and the highest concentration proved to be toxic for the plantlets. Silver nitrate added to the culture medium did not inhibit ethylene production, however, it did inhibit the effect of this hormone on the plantlets. In fact, when high concentrations of silver nitrate were used (300 μm), high amounts of ethylene were detected in the headspace of the vessels and plantlets were actually healthier.

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In Hawaii, the commercial papaya industry is based on cultivars that segregate as females or hermaphrodites. Multiple seedlings are planted and then thinned at flowering to single hermaphrodites at each site. The aim of this study was to increase propagation efficiency by improving our procedure for micropropagation of hermaphrodite plants only. Initially, shoots were multiplied in vented jars on M2 medium, a Murashige and Skoog formulation containing 0.25 μM 6-benzyladenine (BA) and 0.1 μM α-naphthalene acetic acid (NAA). At weekly intervals, micropropagated shoots were either incubated for 4 to 7 days in IBA2 medium containing 20 μM indole-3-butyric acid (IBA) or were dipped in autoclaved rooting powder containing 0.8% IBA (DIP); then, they were placed in M2 until root initials or small roots were visible. After root induction in both treatments, plants were transferred to an in vitro medium containing ½ MSO and 30 g⋅L−1 sucrose in vermiculite (VER). The IBA2 treatment produced 467 potted plants compared to 475 produced by the DIP treatment; however, the average number of days that each treatment required from root induction to potting of rooted plants was not significantly different (IBA2: 52.42 ± 5.65 days; DIP: 51.94 ± 3.61 days). Plants from both treatments were grown in either wet potting medium (500 mL water/300 g potting medium) or damp potting medium (120 mL water/300 g potting medium) to test the effect of moisture content on plant survival and growth after potting. Use of damp rather than wet potting medium resulted in significantly higher plant survival and growth. These results could facilitate more efficient commercial practice for papaya growers.

Open Access

Screening for resistance to mixed infections with pepper huasteco virus (PHV) and pepper golden mosaic virus (PepGMV) was carried out on plants representing wild pepper accessions collected in different states of México. One accession collected in Yucatán (BG-3821) corresponded to Capsicum chinense Jacq., and three collected from Michoacán (BG-3818), Tamaulipas (BG-3820), and Sinaloa (BG-3819) were identified as C. annuum L. Forty-eight plants were initially inoculated with a 1:1 mix of PHV and PepGMV DNAs by a biolistic method. Those plants that did not show typical symptoms after the biolistic method, were inoculated by grafting. Half of the plants (24) were highly susceptible, while the other half expressed different degrees of resistance. Of the resistant individuals, eight plants were asymptomatic and viral DNA of both viruses was detected in low levels. Two individuals showed delayed symptoms 34 days after symptom expression in the control plants. This delay was correlated with an increase in PHV DNA levels when plants became symptomatic. The remaining 14 plants showed symptom remission in newly developed leaves at 31 days postinoculation, and this asymptomatic effect was correlated diminished PHV DNA within the plants. Our results suggest that the resistance shown by some individuals to geminivirus mixed infections (PHV and PepGMV) is likely due to constrains in viral movement.

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The recent increased market demand for locally grown produce is generating interest in the application of techniques developed for controlled environment agriculture (CEA) to urban agriculture (UA). Controlled environments have great potential to revolutionize urban food systems, as they offer unique opportunities for year-round production, optimizing resource-use efficiency, and for helping to overcome significant challenges associated with the high costs of production in urban settings. For urban growers to benefit from CEA, results from studies evaluating the application of controlled environments for commercial food production should be considered. This review includes a discussion of current and potential applications of CEA for UA, references discussing appropriate methods for selecting and controlling the physical plant production environment, resource management strategies, considerations to improve economic viability, opportunities to address food safety concerns, and the potential social benefits from applying CEA techniques to UA. Author’s viewpoints about the future of CEA for urban food production are presented at the end of this review.

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