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Andres A. Estrada-Luna, Fred T. Davies Jr., and Jonathan N. Egilla

The role of mycorrhiza fungi during acclimatization and post-acclimatization of micropropagated chile ancho plantlets was characterized through physiological and plantlet development changes. Regardless of mycorrhizal colonization, the pepper plantlets had initially low photosynthetic rates and poor growth following transplanting ex vitro. During the first days of acclimatization, water deficits occurred as evidenced by drastic reductions in relative water content. Consequently, transpiration rates and stomatal conductance (gs) declined, confirming that in vitro formed stomata were functional, thus avoiding excessive leaf dehydration and plant death. Mycorrhiza had a positive effect on gas exchange as early as day 7 and 8, as indicated by increasing photosynthesis (A) and gs. Mycorrhizal plantlets had reduced levels of abscisic acid (ABA) during peak stress (6 days after transplanting ex vitro), which corresponded with subsequent increases in gs and A. During acclimatization, A increased in both non-colonized and colonized plantlets, with greater rates observed in mycorrhizal plantlets. During post-acclimatization, mycorrhiza colonized 45% of the roots of pepper plantlets and enhanced plant growth by increasing leaf area, leaf dry mass, and fruit number. Mycorrhiza also enhanced total leaf chlorophyll content, A, and nutrient uptake of pepper plantlets, particularly N, P, and K. Early mycorrhizal colonization produced important benefits, which helped ex vitro transplanted plantlets recover during acclimatization and enhance physiological performance and growth during post-acclimatization.

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Andres A. Estrada-Luna, Fred T. Davies Jr., and Jonathan N. Egilla

Micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plants were transferred to ex vitro conditions to study plantlet performance and selected physiological changes that occur during acclimatization and post-acclimatization. The physiology of the plantlets was characterized by measuring leaf gas exchange and water status. Plant growth was determined by assessing plant height, leaf number, total leaf area, relative growth rate (RGR), and leaf, root, and stem dry mass. Measurements were taken at 0, 1, 2, 3, 6, 12, and 24 days after transplanting. After initial transplanting ex vitro to liner pots with soilless media, plantlet wilting was observed that correlated with reduced leaf relative water content (RWC). Water stress was partially alleviated by a reduction in stomatal conductance (gs), confirming that the in vitro formed stomata were functional and able to regulate transpiration (E) to minimize desiccation losses. Because of this stomatal control, plantlets had minimal transplant shock, recovered, and survived. Prior to transplanting, micropropagated plantlets showed heterotrophic/mixotrophic characteristics as indicated by low photosynthesis [(A) 4.74 μmol·m2·s-1]. During acclimatization, RWC, gs, E, and A were significantly lower 2 days after transplanting. However, within 6 days after transplanting, plantlets recovered and became autotrophic, attaining high A (16.3 μmol·m-2·s-1), gs, and E. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acclimatization closely correlated with dramatic increases in plantlet growth.

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Joo Hyun Lee, Yong-Beom Lee, and Kyu Sook Lee

Wasabi japonica plantlets were acclimatized in a hydroponic system to determine effective procedures. The plantlets were cultured on solid Murashige-Skoog medium with 3% sucrose. Shoots that formed roots were transplanted into hydroponic systems: 1) acclimatization in ebb-and-flow (EBB) for subirrigation (medium: granulated rockwool and coir); and 2) acclimatization in deep flow technique (DFT). The plantlets were acclimatized for 5 weeks under two irradiance treatments, 50 and 300 mmol·m-2·s-1. Photosynthetic capacity in high PPF was higher than that in low PPF during acclimatization. Electron transport rate from PS II (ETR) and biomass production increased significantly with increased light availability. The fresh weight, dry weight, and leaf area of plantlets in high PPF were higher than those in low PPF. In particular, the dry weight and ETR of the plantlets grown in high PPF increased more than twice as much as those in low PPF. At 50 mmol·m-2·s-1 PPF, growth indexes, such as number of leaves, leaf length, leaf width, leaf area, fresh weight, and dry weight, were higher in EBB (granulated rockwool) > EBB (coir culture) > DFT. At 300 mmol·m-2·s-1 PPF, those indexes were higher in DFT > EBB (granulated rockwool) > EBB (coir). The Wasabi japonica plantlets acclimatized in a hydroponic system also had a superior performance when they were transferred to the field.

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D.W.A. Hunt, A. Liptay, and C.F. Drury

Host plant selection by Colorado potato beetle [Leptinotarsa decemlineata (Say)] was examined on tomato [Lycopersicon esculentum Mill.] transplants fertilized with varying N, P, and K concentrations during greenhouse production. In choice tests conducted with beetles in the field and the greenhouse, the insect preference for plants increased with increasing leaf tissue N concentration, but P and K concentrations had no effect. Five-day, seedling acclimatization to outdoor spring temperatures before planting reduced the insect preference for plants.

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Mark C. Starrett, Frank A. Blazich, Steven R. Shafer, and Larry F. Grand

Inoculation of microshoots of Pieris floribunda (Pursh ex Sims) Benth. and Hook. (mountain andromeda) with isolates of Hymenoscyphus ericae (Read) Korf and Kernan ericoid mycorrhizal fungi stimulated growth during 1 month in vitro. However, no benefits were apparent after 3 months in a greenhouse. Acclimatization of plantlets of P. floribunda to greenhouse conditions following in vitro inoculation improved survival (42% vs. 16% for controls). The protocol reported herein is similar to procedures utilized currently for micropropagation of various ericaceous species and has potential to improve plantlet survival during acclimatization.

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Trinidad Reyes, Terril A. Nell, Charles A. Conover, and James E. Barrett

Effects of three light intensities (564, 306 and 162 μmol m-2 s-1) and three fertilizer rates (220, 440 and 880 mg/15 cm pot, weekly) were evaluated on acclimatization potential of Chamaedorea elegans. Treatments were applied during four months under greenhouse conditions after which plants were placed indoors (20 μmol m-2 s-1, 21±2C and 50% RH) for two months. Light compensation point (LCP) was significantly reduced by decreasing light intensity and increasing fertilizer rates. Leaf and root fresh and dry weights increased with irradiance while shoots were not affected. Chlorophyll a levels were higher in plants grown under the lowest light intensity. Carbohydrate content is being analyzed and anatomical examination of leaves studied. Plant performance indoors will be discussed. These studies demonstrate that Chamaedorea, a monocot, acclimatizes similarly to dicots.

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Yong Namkung and Byoung Yil Lee

Immature florets were inoculated on MS basal salt media (3% sucrose + 0.8% agar) + 1.0 mg 2,4-D/liter to induce embryogenic callus. Induced embryogenic callus was sieved through serial metal mesh screens (40 and 60 mesh) and placed on the embryo induction media at different concentrations of cytokinins and osmotica. BAP (0.1 mgliter–1) or TDZ (0.001, 0.01, 0.1, and 1.0 mgliter–1) were treated on 1/2 MS (3% sucrose) according to the following schedules: 1) first 2 weeks of treatments, followed by 3 weeks of 1/2 MS (3% sucrose) (FT); 2) first 3 weeks of 1/2 MS (3% sucrose), followed by 2 weeks of treatment (LT); and 3) 5 weeks of treatments. PEG, mannitol (0, 2.5%, 5.0%, 7.5%, and 10.0%), and sucrose (0%, 3%, 6%, 9%, and 15%) also were used as osmotica with ABA (0.05 mgliter–1), respectively. The treatment schedules were FT and LT. Several good quality embryos were produced at 0.001 mg TDZ/liter, 0.1 mg BAP/liter, or 7.5% and 10.0% PEG (only FT). Abnormal embryos were significantly reduced at 7.5% and 10.0% PEG. Leaves of the plants obtained through somatic embryos were compared with those of seed-propagated plants before and after acclimatization using SEM. Epidermal and conductive tissues developed little in the plants before acclimatization; however, they developed gradually after acclimatization and were similar to those of seed-propagated plants.

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Wilfredo Colón-Guasp, Terril A. Nell, Michael E. Kane, and James E. Barrett

The use of abscisic acid (ABA) as an in vitro prehardening treatment to enhance ex vitro acclimatization of Stage III Aronia arbutifolia plantlets was explored. Effects of ABA (0-4 mg·liter-1) pretreatment on ex vitro shoot growth, leaf carbon assimilation (LCA) and nonstructural carbohydrate content were evaluated during plantlet acclimatization under two photosynthetic photon flux (PPF) levels (450 and 650 μmol·m-2·s-1). Stage III plantlets rooted in the presence of ABA exhibited both shoot growth inhibition and transient negative LCA rates at time of transfer ex vitro. Regardless of treatment, maximum LCA rates were achieved by day 20 post-transplant. Pretreatment with ABA had no effect on stem or leaf starch content at time of transplant, however, leaf and stem soluble sugar content was higher in ABA treated plantlets than controls. Further suppression of shoot growth and alteration in the pattern of stem starch utilization occurred at the higher irradiance level. These results indicate that ABA pretreatments provide no physiological advantage that would facilitate ex vitro acclimatization of Aronia plantlets.

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J.M. Sarracino, R. Merritt, and C.K. Chin

Two foliage plant species, Leea coccinia L. and Leea rubra L., exhibited lower light compensation points and faster rates of acclimatization than Ficus benjamina L. when moved from full sun to dense shade, i.e., from 15.7 to 0.26 or 0.09 mol·m·-2day-1. Light compensation points were reduced up to 75% for L. coccinia and 71% for L. rubra after 25 days under these conditions. Uptake of CO2 increased from 65% to 179% and 34% to 118% for L. coccinia and L. rubra, respectively, while respiration rates were reduced from 73% and 76% to 59% to 68%, respectively. Ficus benjamina plants died under similar conditions.

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J. Adelberg, M. Kroggel, and J. Toler

Hosta ×hybrid Tratt. `Blue Cadet' and Hosta tokudama Tratt. `Newberry Gold' were micropropagated in shaken liquid culture and on agar media, in conventional vessels and vessels modified for ventilation in vitro. Acclimatization under intermittent mist and growth in an outdoor nursery during the late spring and summer were monitored by dry weight analysis of sample plants every 4 days for a 60-day period (ex vitro growth). Results for `Newberry Gold' were 1) in vitro shoot growth was greater in liquid than agar culture, regardless of vessel; 2) shoots from agar or liquid culture grew at similar rates ex vitro; 3) ex vitro root growth was greater for liquid than agar cultured plants, regardless of vessel type. Results for `Blue Cadet' were 1) in vitro and ex vitro shoot growth was greater in liquid than agar culture regardless of vessel type and 2) ex vitro root growth was greatest for liquid cultured plants from conventional vessels. Ventilated vessels were generally beneficial for agar but not liquid culture. Benefits of liquid culture for micropropagation of Hosta found in vitro are at least maintained and sometimes enhanced during ex vitro growth in the mist bed and nursery.