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Terril A. Nell, Ria T. Leonard, and James E. Barrett

Production irradiance levels on growth, light compensation point (LCP), dark respiration (DR), and interior longevity of potted chrysanthemum (Demfranthema grandiflora Tzvelev. cvs. Iridon and Mountain Peak) and poinsettia (Euphorbia pulcherrima Wind. cvs. Annette Hegg Dark Red and Gutbier V-10 Amy) were determined. LCP and DR were measured at anthesis and during acclimatization to interior conditions (10 μmol·s-1·m-2). Days to flowering, inflorescence diameter, total chlorophyll, and interior longevity of chrysanthemum increased when maintained at a mean maximum photosynthetic photon flux density (PPFD) of 500 μmol·s-1·m-2 compared to plants shifted to 300 or 100 μmol·s-1·m-2 8 weeks after planting. LCP and DR were highest at anthesis and were reduced 38% and 49%, respectively, for chrysanthemum and 19% and 42%, respectively, for poinsettia within 3 days in interior conditions. Chrysanthemum plants shifted to 300 μmol·s1·m-2 during production had lower LCP and DR rates at anthesis and throughout time in interior conditions compared to plants maintained at 500 μmol·s-1·m-2. The acclimatization of chrysanthemum to reduced production PPFD is of little significance because interior longevity is reduced. No differences were found in the LCP or DR of poinsettia or chrysanthemum cultivars that differ in interior performance, demonstrating that these physiological characteristics are not good indicators of interior longevity for chrysanthemum and poinsettia.

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Rida A. Shibli and M.A.L. Smith

Ohelo (V. pahalae Skottsb.) and bilberry (V. myrtillus L.) shoots were regenerated via direct organogenesis from whole leaves and leaf sections and also from hypocotyl explants of bilberry. Explants preincubated for 1 to 2 weeks in darkness yielded ≈75% regeneration frequencies and the highest number of regenerating shoots/explant on TDZ-supplemented media (0.9 to 2.7 μm). When 2iP or zeatin were substituted as the cytokinin source, frequencies of regeneration and shoot productivity were significantly lower. Explants held under constant illumination (no dark pretreatment) had significantly lower regeneration frequencies in all tested cytokinin-supplemented media. 2,4-D stimulated callus formation, but did not support regeneration from vegetative explants. Cells from callus and suspension cultures did not exhibit regeneration in any of the media that supported organogenesis from leaves. Regenerants were successfully micropropagated, although callus formation caused by zeatin and high 2iP levels interfered with shoot proliferation. Zeatin induced hyperhydricity in shoots from both species, but more severely in ohelo. Ex vitro rooting after treatment with 4.9 μm IBA or 5.4 μm NAA was 95% and 60% successful for bilberry and ohelo, respectively, and plants were readily acclimatized after an interval in a fog chamber. Bilberry microshoots also rooted in vitro in the absence of growth regulator treatment. Chemical names used: 1H-indole-3-butanoic acid (IBA); N-(3-methyl-2-butenyl)-1-H-purine-6-amine (2iP); 6-furfurylaminopurine (kinetin); 1-naphthaleneacetic acid (NAA); thidiazuron=1-phenyl-3-(1,2,3-thiadiazio-5-yl)urea (TDZ); 2,4-dichlorophenoxyacetic acid (2,4-D); 6-(4-hydroxy-3-methylbut-2-enylamino) purine (zeatin).

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

The effect of irradiance and fertilizer level on the acclimatization of Chamaedorea elegans Mart. was studied. Chamaedorea elegans was grown for 4 months in 1.6-liter pots under 162, 306, or 564 μmol·m–2·s–1 and fertilized weekly with 20N–4.7P–16.6K soluble fertilizer at 220, 440, or 880 mg/pot. At the end of the production period, plants were moved to interior rooms and maintained for 2 months at 20 μmol·m–2·s–1 for 12 h daily at 21 ± 1C and a relative humidity of 50% ± 5%. At the end of the production phase, the light compensation point (LCP) and the concentration of nonstructural carbohydrates were lower, and chlorophyll concentration was higher the lower the irradiance level. Increasing fertilizer concentration decreased the number of fronds, LCP, and nonstructural carbohydrates. After 2 months in the interior environment, LCP and number of fronds of C. elegans did not differ among treatments. Chlorophyll concentration of plants grown under 564 μmol·m–2·s–1 had increased 61%, while starch in the stem had decreased 43% relative to the concentration found at the end of the production period. In C. elegans grown under 306 μmol·m–2·s–1, stem starch depletion was only 13% during the interior evaluation period. These results indicated that C. elegans grown under the highest irradiance level used reserved carbohydrates in the interior environment while adjusting to low light and producing new leaves. Chamaedorea elegans was best acclimatized at the intermediate irradiance and medium fertilizer concentration.

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Song-jun Zeng, Zhi-lin Chen, Kun-lin Wu, Jian-xia Zhang, Cheng-ke Bai, Jaime A. Teixeira da Silva, and Jun Duan

culture flasks per replicate with 20 protocorms or PLBs in each flask. Greenhouse acclimatization. The effects of two transplanting methods and two planting media on ex vitro plantlet acclimatization were studied. Plantlets with roots 2 cm or longer were

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James R. Ault

Shoot initiation and multiplication were obtained in vitro from immature flower bud and leaf explants of Veltheimia bracteata Bak. `Lemon Flame' and from leaf explants of V. bracteata `Rosalba' cultured on a Murashige and Skoog (MS) medium supplemented with sucrose at 30 g•L–1, and either 8.87 μm BA plus 0.54 μm NAA or 8.87 μm BA plus 5.40 μm NAA. Shoot initiation and multiplication was obtained from a single leaf explant of Veltheimia capensis (L.) DC. on MS medium with 8.87 μm BA plus 0.54 μm NAA. Shoots of the three genotypes rooted on subculture to medium with 0.0, 4.14, or 8.29 μm K-IBA or 0.0, 4.46, or 8.92 μm K-NAA. Maximal rooting was 98% for V. bracteata `Lemon Flame', 95% for V. bracteata `Rosalba', and 98% for V. capensis, from medium with 4.46 μm KNAA. Rooted shoots were acclimatized for 3 to 4 weeks. Overall survival percentage was 69% for V. bracteata `Lemon Flame', 65% for V. bracteata `Rosalba', and 83% for V. capensis. Chemical names used: 6-benzyladenine (BA); potassium salt of indole-3-butyric acid (K-IBA); potassium salt of 1-naphthaleneacetic acid (K-NAA); 1-naphthaleneacetic acid (NAA).

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Kourosh Vahdati, Charles Leslie, Zabihollah Zamani, and Gale McGranahan

In vitro rooting of three commercial cultivars of Persian walnut (Juglans regia L.), `Sunland', `Chandler', and `Vina', was examined using a two-phase rooting procedure: root induction in the dark on Murashige and Skoog (MS) medium with 15 μm IBA followed by root development in the light on a mixture of one-quarter strength Driver Kuniyuki Walnut (DKW) basal medium and vermiculite (1:1.25, v/v). Rooting percentages were: `Sunland' (94%), `Chandler (55%), and `Vina' (27%). A positive relationship was observed between the vigor of cultivars and rooting ability, but shoot length did not affect rooting success. Rooting was optimum when shoots were cultured on root induction media for 6 to 8 days. Increasing the sucrose level in the root induction medium to 40 g·L-1 improved rooting, and shoots induced to root at 22 °C rooted more readily than those induced at 30 °C. Either increasing or decreasing the nitrogen level in the multiplication medium had a negative effect on rooting. Rooted walnut shoots often cease growth during acclimatization, resulting in shoot rosetting. Spray application of Promalin® (25 mL·L-1) caused buds to break and induced elongation of shoots. Chemical name used: indole-3-butyric acid (IBA).

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Juan C Díaz, Kenneth Shackel, and Ellen Sutter

Apple plantlets were cultured in a MS medium with agar and transplanted to a soilless mix. Before transplanting, plantlets were acclimatized in a chamber where humidity was linearly decreased from 99% to 75% (21 C) over a period of four days. Gas exchange measurements were made at 95% RH (21 C) and at an irradiance of 350 μmol m-2 s-1. Leaf conductance (g1) was measured with a porometer and net photosynthesis (Pn) with an IRGA. At the end of the gas exchange measurements, shoot relative water content (RWC) was determined. The results showed that plant water status was an important factor for plant survival and growth after transplanting. Acclimatization before transplanting allowed the plant to maintain a higher RWC, probably because of a better stomatal control of transpiration. Such higher water status was associated with higher growth rates in acclimatized than in non-acclimatized plants. There was a positive correlation of RWC with both a and Pn. Transplanted plants had higher values of g1 and Pn compared to in vitro plantlets. Photosynthesis of in vitro plantlets was limited by both stomatal and nonstomatal factors.

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Marvin Pritts and Dorcas Isuta

Previous findings reveal that rooting and acclimatization of apple and blueberry plants is often difficult, inconsistent and inefficient. This experiment was set up in a fog chamber lo investigate the effects of CO2 enrichment (CDE) and irradiance on unrooted stage II microshoots. Two CO2 and 3 light levels tested were: 1350 +/- 150 (+ CDE), and 450 +/- 50 (- CDE) ppm; 30 +/- 5 (low), 55 + 10 (medium), and 100 + 20 (high) umolm-2s-1 respectively. Cultivars assessed were Berkeley and Northsky for blueberry. G65 and NY30 for apple. Blueberry microshoots acclimatized successfully and gave between 90 to 100% rooting and survival rate. Apple microshoots acclimatized and rooted slowly, exhibited great sensitivity to in vivo conditions and gave between 40 to 100% rooting and survival rate. High light induced photo-inhibition which disappeared after complete acclimatization. There was a significant difference between low light and the other two light levels. The effect of CDE was dependent on cultivar. In most cases, high light (-) CDE gave the most vigorous growth (highest plant dry weight and leaf area). There was a significant difference between (+) CDE and (-) CDE at low and medium light, but none at high light. Low light (-) CDE and medium light (+) CDE were superior over low light (+) CDE and medium light (-) CDE. respectively. Stalling out in apple microshoots was corrected by GA sprays.

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Juan C. Díaz-Pérez, Kenneth A. Shackel, and Ellen G. Sutter

Little is known about the physiological changes that occur during acclimatization and how these changes influence plant survival and growth in the new environment. In particular, it is unclear to what extent in vitro-formed roots are functional in water uptake, particularly when the plantlet is exposed to conditions of increasing evaporative demand. Tissue-cultured shoots and plantlets (shoots with roots) were acclimatized by exposing them to a linear reduction in relative humidity (RH) from 99 % to 75%over 4 days. When conductance was measured at 95% RH (21 C), in vitro shoots and plantlets showed a very high initial conductance, followed by a gradual decline, reaching steady state in 12 hours. Acclimatized shoots and plantlets had a 50% lower initial conductance compared to nonacclimatized ones, and reached steady state in 4 hours. The reduction in conductance as a result of acclimatization most likely contributes to a reduced transpiration under conditions of increased evaporative demand. Roots formed in vitro were associated with a higher plant water status, suggesting that these roots were functional in water uptake. Relative water content of the shoot was positively correlated with leaf conductance and net photosynthesis. We suggest that tissue-cultured plantlets behave as hydraulically integrated units, in which there must be a coordination between control of water loss by the shoot and uptake of water by the root to maintain a favorable plant water balance. Our results also indicate that methods that use excised shoots or leaves to determine transpiration gravimetrically may not accurately represent the stomatal water loss characteristics of tissue-cultured plants.

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Carmen Valero Aracama*, Michael E. Kane, Nancy L. Philman, and Sandra B. Wilson

A sea oats (Uniola paniculata L.) micropropagation protocol was previously developed for 28 genotypes that favored multiplication and rooting of shoots in vitro. However, microcutting size, morphology, and acclimatization ex vitro varied considerably among genotypes. In the present study we evaluated the effect of Stage III duration on in vitro morphology, biomass production, and ex vitro survivability of easy-(EK 16-3) and difficult-to-acclimatize (EK 11-1) sea oats genotypes. After 3, 6, and 9 weeks at Stage III, survivability of microcuttings was 85%, 96% and 98% for EK 16-3, and 2%, 27% and 40% for EK 11-1, respectively. After 9 weeks Stage III, EK 16-3 microcuttings had higher shoot dry weights but lower root dry weights than in EK 11-1. Moreover, roots in EK 11-1 were fewer but longer than in EK 16-3. Leaf production was similar in both genotypes. However, leaf elongation was significantly inhibited in EK 11-1, in which 95% of the leaves were ≤ 15 mm long in contrast with EK 16-3, with 50% leaves ≥ 16 mm long after 9 weeks Stage III. Light microscopy examinations showed anatomical similarities between EK 16-3 in vitro leaves and mature ex vitro leaves. Conversely, short in vitro leaves of EK 11-1 exhibited mesophyll disruption and reduced cuticle development. Conceivably, the short leaves had limited photosynthetic competency, thereby reducing ex vitro survival of rooted EK 11-1 microcuttings.