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Mario Valenzuela-Vázquez, Geno A. Picchioni, Leigh W. Murray, and Wayne A. Mackay

of the floral apical meristem ( Picchioni et al., 2007 ). The increase in RLR appears to reflect this developmentally regulated function as a source organ rather than only an increase in permeability per se. Only recently have mineral-exporting traits

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C. A. Clark, R. A. Valverde, J. A. Wilder-Ayers, and P. E. Nelson

Symptoms of chlorotic leaf distortion (CLD) develop on vigorously growing sweetpotato (Ipomoea batatas) plants during sunny weather. They include chlorosis and twisting of young, expanding leaves and the appearance of white material on the adaxial leaf surfaces. The white material consisted of extramatrical fungal mycelia and Fusarium macroconidia. Fusarium lateritium Nees was isolated from surface-sterilized vine segments, leaf primordia, apical meristems, flower parts and true seeds of plants with CLD. Meristem-tip-culture-derived plants (mericlones) did not develop symptoms when grown for extended periods under disease-conducive conditions in the greenhouse. The fungus was not isolated from mericlones or other plants which had remained symptomless in the greenhouse but was isolated from lower nodes of symptomless plants from growers' fields. Symptoms developed on 84% of 185 mericlones of nine sweetpotato genotypes inoculated with F. lateritium isolated from CLD-affected plants. The pathogen was reisolated only from inoculated mericlones.

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Richard L. Harkess and Robert E. Lyons

BA and GA4+7, were applied to vegetative, mature Rudbeckia hirta plants at the beginning of long days (LD). There were no synergistic effects, but BA inconsistently affected branching and had no effect on flowering. Floral initiation of the terminal inflorescence was promoted by GA4+7, although axillary inflorescences were not. Increasing GA4+7 levels decreased the time to terminal inflorescence anthesis. However, the interval between the terminal and second axillary inflorescence anthesis was increased. The net result was no significant effect on the time to second axillary inflorescence anthesis. Gibberellins may enhance the LD effect on the apical meristem of Rudbeckia, but axillary meristems, which initiate later, remained unaffected. Chemical names used: benzyladenine (BA), gibberellin4+7, (GA4+7).

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Rina Kamenetsky and Jacob Blaustein

The annual life cycle and development of the monocarpic shoot of some ornamental Allium species from Central Asia and the Mediterranean area have been followed from the time of meristem dome initiation in the axil of a mother plant leaf, through formation of scale, leaf and flower primordia. There are three periods of meristem activity from apex initiation to flower formation. Detailed analysis of inflorescence development has been carried out by Scanning Electronic Microscope (SEM). The life span of the Allium monocarpic shoot can be as long as 18 months. Climatic variations between Central Asian and Mediterranean areas lead to differences in the time of leaf sprout and flowering of species from the same taxonomic group. The principal mechanism of floral initiation is similar for species from both areas. Knowledge of the structure and development of the shoot will be useful for improvement of an optimal program of ornamental Allium cultivation.

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B.L. Goulart, K. Demchak, W.Q. Yang, C.M. Stevens, and Y. Dalpe

Past experiments have proven that meristem tip-cultured blueberry plantlets are extremely difficult to inoculate using laboratory-grown cultures of existing known isolates of Hymenoscyphus ericae, Scytalidium vaccinii, and Oidiodendron griseum; fungi that have been previously established as ericoid mycorrhizal symbionts. An experiment using both seedling and meristem tip-cultured plantlets was conducted using these proven fungal symbionts from the Canadian Fungal Culture Collection (DAOM), as well as fungi isolated from local blueberry populations at Little Flat, Pa. Treatments included inoculation using soil from the Little Flat population, the same soil (autoclaved), autoclaved soil that was reinoculated with fungi, as well as axenic treatments using H. ericae, S. vaccinii, O. griseum, Little Flat Hymenoscyphus sp., Little Flat Scytalidium sp., and Little Flat Oidiodendron sp. Sampling after 21 days revealed that only the nontreated soil plantlets were infected (≈4%). Results from later sampling dates will be presented, and the mechanism of infection discussed.

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R.J. Griesbach

The apical meristems of Calanthe orchid embryos were exposed to 1 mg/ml pBI-121 DNA in an electric field. pBI-121 contains the GUS marker gene glucoronidase under the control of the 35 S cauliflower mosaic virus promoter. A pipette containing 0.3% agarose and acetate buffer containing the DNA was placed on one end of the embryo; while the opposite end was in contact with a pipette containing only buffer and agarose. Uptake of the DNA into the meristem was monitored by 4′6-diamidino-2-phenylindole (DAPI) fluorescence. Optimal uptake occurred after 10 min of electrophoresis at 10 volts and 0.5 milliamps. Under these conditions, 55% of the embryos survived the treatment and 57% of those which survived were transformed as measured by GUS-positive staining. Leaves from 6 month old plants which developed from the transformed embryos expressed specific patterns of GUS staining.

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Naza Sh. Azizbekova, Stefanie L. Butland, Brian E. Ellis, and Christia M. Roberts

The growth cycle of Scilla peruviana L. involved the development of two generations of daughter bulbs enclosed within each mother bulb. Flower initiation of the primary daughter bulb took place in June as the mother bulb apparently entered dormancy. Floral differentiation was complete by late October, by which time the apical meristem of the secondary daughter bulb had developed for 3 months inside the primary daughter bulb. The complete cycle of ontogenesis, from meristem initiation to flowering, occurred without interruption and required 20 months. Small zones of meristematic cells detected at the bases of bulb scales may be the origin of adventitious bulblets in this species. This detailed cytological study enabled the development of an effective commercial forcing program for S. peruviana.

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Susan S. Han, Abraham H. Halevy, Roy M. Sachs, and Michael S. Reid

Exposure of dormant corms of Triteleia laxa `Queen Fabiola' to 20 ppm C2H4 for 7 days promoted flowering of small corms and resulted in increased apical meristem size, early sprouting, early flowering, more flowers per Inflorescence, and increased fresh weight of daughter corms and cormels. The respiration rate of the C&treated corms increased to four to five times that of the controls during the 7-day treatment, declined markedly after termination of the C2H4 treatment, but remained higher than that of the controls. The C2H4 effects were associated with increased growth rate and consequently a greater final size of the apical meristem (determined by scanning electron microscopy). Leaves produced by C2H4-treated corms were wider, longer, and weighed more than those of the controls.

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Norberto Maciel and Eybar Rojas

The shoot apex from plants of Heliconia bihai (L.) L. and H. latispatha Benth. growing under natural inductive conditions, and two shade-loving (60% and 0%) at different growth stages (one to six or eight expanded leaves) was studied. Observations were made using a light microscope, in 15-μm-thick sections. The analysis included changes in 1) size and shape of the meristem, 2) shape, ubication of new leaves, spathes, and flowers in the apex, and 3) relation between these characteristics, the condition of the apex (vegetative, transitional, and generative), and the plant growth stages. The anatomical structures of the shoot apex (meristem, leaves, and flowers primordias) are illustrated by photomicrographs. The meristem change in size and shape with grow up expanded leaf number. The condition of the apex was related to the total leaf number. The total leaf number was five or six in H. bihai under 60% and 0 % shade levels and 8 in H. latispatha at both shade levels. The apex reaches the generative stage when the plant has a minimum expanded leaf number of four (at 60 % shade) and five (0 %) in H. bihai and five in both shade conditions in H. latispatha. After this, the inflorescence started progressively to raise above the rest of rhizome.

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Liping Wang, Guoping Wang, Ni Hong, Rongrong Tang, Xiaoyun Deng, and Hong Zhang

Apple stem grooving virus (ASGV) and apple chlorotic leaf spot virus (ACLSV) are two major viruses of pear. In this study, in vitro thermotherapy was carried out at 37°C for 25, 30 and 35 days followed by subculturing of meristem tips of different sizes to eliminate ASGV and ACLSV from pear plants. Virus titers in heat-treated shoot tips were evaluated by ELISA testing of regenerated plants. Results showed that thermotherapy for 35 days significantly decreased the titer of ASGV and ACLSV in cultures regenerated from tips of main and axillary shoots, especially in those from explants 1 mm in length from the tip of meristems. Dot-blot hybridization of biotinylated cDNA probes derived from ACLSV and ASGV was used to detect these viruses in crude tissue extracts of in vitro-grown pear plants. Intense signals were consistently detected in untreated plant samples equivalent to less than 0.5 mg tissue. Comparison of signals from dot-blot hybridization and ELISA absorbance values (A405) confirmed that dot-blot hybridization had a higher sensitivity than PAS-ELISA. Dot-blot hybridization could detect viruses with a titer below the threshold level of ELISA. These results indicate that dot-blot hybridization is a useful tool for large-scale surveys of viruses, which facilitates the production of virus-free propagation materials in certification and sanitation programs. Results of PAS-ELISA and dot-blot hybridization showed that high virus elimination efficiency was achieved by a combination of thermotherapy for 35 days and in vitro culture of 1 mm meristem tips.