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R.C. Apter, E.L. McWilliams, and F.T. Davies Jr.

One-node explants and one-node stem cuttings of Asian jasmine [Trachelospermum asiaticum (Siebold & Zucc.) Nakai] were rooted, respectively, in vitro [tissue culture (TC)] or by conventional macropropagation (MACRO). The TC and MACRO stem bases were then analyzed for differences in the time-course sequence of 1) root primordia initiation and development and 2) adventitious root xylem development and root-to-shoot xylem connections. Early root primordia were observed at Day 3, and, by Day 7, root-to-shoot xylem connections were equally developed in TC and MACRO systems. Continued development and emergence of adventitious roots were observed at Days 8 to 10. At Days 13 and 18, when viewed using scanning electron microscopy, TC root hairs were morphologically thicker and one-third to one-half the length of MACRO root hairs. There was no apparent difference in root-hair density. Inferior TC root-hair length may be a factor in the acclimation of TC-generated plantlets.

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Nancy Philman, Murdock Ray Gillis, and Michael E. Kane

Commercial micropropagation of wetland plants used for habitat restoration provides an alternative to field collection and facilitates production of difficult-to-propagate species and possibly selection of ecotypes that are physiologically adapted to specific habitat conditions. Knowledge of the degree of ecotypic variation within and between wetland populations is very limited. The feasibility of screening ecotypic differences in growth of micropropagated wetland plants, following acclimatization, was examined using Sagittaria latifolia Willd. (Duck-potato), a highly variable rhizomatous herbaceous wetland species that is widely distributed in southeastern Canada and the eastern United States. Plants were obtained from populations in Rhode Island, North Carolina, South Carolina, and Florida. Stage I cultures of each Sagittaria latifolia ecotype were established from surface-sterilized rhizome shoot-tips cultured in a liquid basal medium (BM) consisting of half-strength Murashige and Skoog mineral salts, 0.56 mM myo-inositol and 1.2 μM thiamine supplemented with 87.6 mM sucrose. Stage I cultures were indexed for cultivable bacteria prior to clonal multiplication of each ecotype by rhizome production on agar-solidified BM supplemented with 1.1 μM benzyladenine (BA). At 4-week intervals for 24 months, Stage II microcuttings of each ecotype were acclimatized and rooted in soilless growing medium under intermittent mist for 10 days. Plantlets were transferred to a shadehouse (50% sunlight reduction) and maintained under prevailing environmental conditions. Plant height, leaf length and number, rhizome number, corm number and weight, and flowering were determined 6 weeks post-transplant. Significant seasonal differences in leaf growth, rhizome production, corm formation and flowering were observed between ecotypes. During the growing season, induction of corm formation occurred progressively earlier in the more northern ecotypes.

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D. J. Donnelly and W. E. Vidaver


CO2 uptake and various leaf parameters were examined including photosynthetic pigment content (chlorophyll a, b, and total carotenoids), fresh/dry weight, percentage of water content, gram dry weight/area, and total plantlet leaf areas of an aseptically cultured clone of red raspberry (Rubus idaeus L.) incubated at 5 light intensities, from 2 to 6 klx. Cultured plantlets demonstrated relatively low levels of CO2 uptake, averaging 2.5 mg CO2 dm–2hr–1 and rarely exceeding 4 mg CO2 dm–2 hr–1 at saturating light intensities. Pigment content was higher in plantlets incubated at lower light intensities (2 to 4 klx). Cultures incubated at 3 klx were evaluated both at the time of transfer to soil and 1 month later. Plantlet leaves retained from culture could be distinguished from new leaves by tagging all plantlet leaves prior to soil transfer; both were assessed separately 1 month after transplantation. Leaves retained from culture, 30% of the total leaf area of transplants, contributed less than 10% of the CO2 uptake at 3 klx. These leaves accounted for 10% to 30% of the total leaf area at higher light intensities but were net respirers. There was an increase in dry matter accumulation at 6 and 9 klx in these tagged leaves, but not at 3 klx. Continued accumulation of dry matter by the tagged leaves can be only at the expense of photosynthetic activity of the newly formed leaves. New leaves of transplants had a greater dry matter accumulation at 9 klx and a pigment content greater than the tagged leaves. Their pigment content was similar to that of young, control plant leaves. Transplants were capable of uptake rates of 5–7 mg CO2 dm–2 hr–1 or 50% of field control rates. The photosynthetic contribution of the leaves from culture was small or negative. The first new leaves formed in soil were transitional with intermediate capability. Acclimatization to the soil environment was time dependent and required the production of new leaves initiated in the new environment.

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Samir Debnath*

The morphological development of lingonberry (Vaccinium vitis-idaea L.) plants propagated either by conventional softwood cuttings or by in vitro shoot proliferation from nodal explants or by shoot regeneration from excised leaves of micropropagated shoots, was studied in cultivars `Regal', `Splendor', and `Erntedank'. Significant differences were observed between the treatments. In vitro-derived plants produced more shoots branches and rhizomes in contrast to conventional cuttings which rarely produced rhizomes. Plants propagated from cuttings had a lower number but vigorous shoots and thicker rhizomes than in vitro-derived plants. Source propagule had significant effect on multiplication rate. Another experiment evaluated the effect of indole-3-butyric acid (IBA) application to softwood cuttings on subsequent rooting, shoot development, and rhizome production. Treating cuttings with IBA did not significantly improve rhizome formation and elongation. In vitro culture on nutrient medium apparently induces the juvenile branching characteristics that favored rhizome production. The advantage of rhizome production of in vitro-derived plants over stem cuttings varied among genotypes.

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Samir C. Debnath

The growth and development of lingonberry (Vaccinium vitis-idaea L.) plants propagated either by conventional softwood cuttings or by in vitro shoot proliferation from nodal explants and by shoot regeneration from excised leaves of micropropagated shoots, were studied in cultivars `Regal', `Splendor', and `Erntedank'. Significant differences were observed between the treatments. After 3 years of growth, the in vitro-derived plants produced more stems, leaves, and rhizomes than the conventional cuttings which rarely produced rhizomes. In vitro culture on nutrient medium apparently induces the juvenile branching characteristics that favor rhizome production. This increase in vegetative growth and rhizome yield of in vitro-derived plants over stem cuttings varied among genotypes.

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Imed Dami and Harrison Hughes

Micropropagated grapes (Vitis sp. `Valiant') were subjected to water stress while rooting with the addition of 2% (w/v) PEG 8000. PEG-treated plantlets exhibited reduced growth, as compared to control (in vitro, no PEG), but developed greater leaf epicuticular wax. PEG-treated plantlets had three times the wax level of control. Although treated plantlets showed changes in leaf anatomy, no effect on stomatal frequency or stomatal index was evident. Differences in epidermal cell configuration were also observed among leaves from different treatments. PEG-treated plantlets resembled those grown in the greenhouse, morphologically and anatomically, and exhibited a higher survival rate than control upon transfer to the greenhouse.

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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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M.A. Norton and R.M. Skirvin

Chimeral `Thornless Evergreen' (CTE), (Rubus laciniatus Willd.) somaclones selected in 1983 and field planted in 1985 were reexamined in 1992 for various vegetative and reproductive characteristics. Two major types of thornless (prickle-free) plants, intermediate-sized (`UI 6-6' = `Everthornless') and dwarf (`UI 6-4'), originally selected from a chimeral thornless parent plant, were compared with thorny plants. The intermediate and dwarf somaclones have maintained their distinctive habits over 7 years' growth in the field, indicating that their growth habits are stable and not a transient effect of tissue culture. Although the thornless somaclones remained thornless, the degree and type of prickle-like structures varies considerably, indicating that the thornless gene (S te) does not entirely suppress the production of prickles, but apparently alters their development. Increasing suppression was directly related to increasing dwarfism, suggesting a link between thornlessness and internode length.

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Lawrence W. Zettler, Sarah B. Poulter, Kris I. McDonald, and Scott L. Stewart

of transplanted seedlings ex vitro ( Anderson, 1991 ; Ramsay and Dixon, 2003 ), and it is conceivable that the same could be true for epiphytes. Moreover, the act of releasing mycotrophic seedlings in situ could also result in the release of suitable

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Jin Cui, Juanxu Liu, Min Deng, Jianjun Chen, and Richard J. Henny

ex Fr.) has become the most common disease of arrowhead vine. This opportunistic airborne fungal pathogen particularly occurs during the ex vitro rooting of microcuttings after shoot culture because the cutting base is especially susceptible to this