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  • Author or Editor: C.D. Robacker x
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Pierce's disease, caused by the bacterium Xylella fastidiosa Wells et al., is widespread among muscadine grapes (Vitus rotundifolia Michx). To determine whether shoot-tip culture would be effective in eliminating X. fastidiosa, shoot tips of infected grape plants were cultured on Murashige and Skoog medium amended with 9 μm benzyladenine. Shoots and callus that developed tested negative for the presence of X. fastidiosa. Shoot-tip culture appears to be a promising method of obtaining muscadine grape plants free of Pierce's disease. Chemical name used: 6-benzylaminopurine (benzyladenine).

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A micropropagation system to obtain plants from inflorescences of pampas grass (Cortaderia selloana Schult. `Pumila') was developed. Factors examined included developmental stage of inflorescence cultured and growth regulator combinations and concentrations that support explant establishment, shoot regeneration, and rooting. Immature inflorescences ≈300 mm long formed many shoot primordia when initially cultured on Murashige and Skoog basal medium containing 4.5 μm 2,4-D and 8.9 μm BA and subcultured to medium with 0.4 μm 2,4-D and 4.4 μm BA. Thereafter, monthly transfer to a medium without growth regulators yielded about three shoots per tube per month for more than 6 months. Most shoots rooted spontaneously and were easily hardened to greenhouse conditions. Field-tested plants flowered within 2 years and nearly all appeared identical to the parent cultivar. With this technique, several thousand plants can be obtained from a single inflorescence in 1 year. Chemical names used: N -(phenylmethyl)-1 H -purine-6-amine (BA); (2,4-dichlorophenoxy)acetic acid (2,4-D).

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Nineteen cultivars of muscadine grape (Vitis rotundifoli a Michx.) were divided into three classes based on the mean number of shoots developed during micropropagation. The cultivars in each class were then compared for pedigree similarities and common ancestors were identified. It was determined that the difficult to propagate class always had close direct lineage to either `White Male' or `Scuppernong', both selections from the wild. The intermediate class tended to be composed of newer cultivars which were more distantly related to `White Male' and `Scuppernong'. The easy to propagate class had diverse family histories and none of them included either `White Male' or `Scuppernong' for three or more generations. It is hypothesized that some factor, yet undetermined, has an influence on the ability of muscadine grape to be micropropagated.

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Screening of muscadine grape (Vitis rotundifolia) plants in vineyards has revealed that many plants carry Xylella fastidiosa; under suitable conditions, this bacterium causes Pierce's disease which can result in considerable loss. To determine whether propagation of muscadine through shoot tips would eliminate X. fastidiosa, plants were injected with this bacterium. After demonstrating infection, shoot tips were collected and cultured. according to the technique of Barlass and Skene (1978). Plants which were regenerated were found to be free of the bacterium. To determine whether this shoot-tip culture technique would be effective for propagation of a diverse group of muscadines, 19 cultivars were tested. Three of the cultivars failed to produce any plants, and several others reproduced at a low rate of efficiency. In an attempt to improve the rate of regeneration, several modifications to the technique were tested. For most cultivars, better initiation occurred on liquid medium, more shoots were produced with BA than with 2iP, and the addition of adenine sulfate and sodium phosphate improved the regeneration frequency.

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Immature inflorescences of Miscanthus sinensis Andress. `Gracillimus', `Variegatus', and `Zebrinus' were cultured on modified MS medium with 9.0 μm 2,4-D, 20 g sucrose/liter, 2.0 g Gelrite/liter, and 0.75 g MgCl2/liter. Organogenesis was observed 8 to 12 weeks after callus initiation. Shoots were rooted on half-strength MS medium without growth regulators. After rooting, tillers were initiated. When transferred to soil, plants matured to flowering quickly and retained their variegation patterns. Propagation through in vitro tillering is suggested. Chemical name used: 2,4-dichlorophenoxyacetic acid (2,4-D).

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The genus Abelia contains ≈30 species, but A. × grandiflora, its cultivars, and A. `Edward Goucher' are the primary taxa grown. The nursery industry has stated that Abelia R. Br. taxa are important economically, and new selections or cultivars with increased cold hardiness, richer pink-rose flower colors, unique foliage colors, and compact habits are desired. Breeding and selection work in the genus is very limited due in part to limited access to germplasm. Pollen storage enables breeders to cross taxa with incongruent flowering cycles, save time and resources by eliminating the need to grow vast amounts of plant material, and incorporate otherwise unavailable germplasm into a breeding program. An experiment was conducted to determine the optimum levels of temperature and humidity for the long-term storage of A. chinensis and A. × grandiflora `Golden Glow' pollen. Temperature and humidity levels were analyzed by incubating undesiccated pollen of a given taxon at four humidity levels (0%, 50%, 80%, and 100%) for 72 h at 5 °C. Following incubation, the pollen was stored in glass vials at each of the following temperatures: 5, -20, and -70 °C. All combinations of temperature and humidity were tested. Pollen viability was assessed after 60 days by in vivo germination tests on styles. Abelia chinensis pollen germinated following storage at all temperature and humidity levels. Pollen of A. × grandiflora `Golden Glow' pollen germinated following all treatments except storage at -20 °C.

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Deciduous azaleas have been gaining popularity because of their showy floral displays and adaptability to adverse environmental conditions. However, an absence of distinguishing morphological characteristics, combined with the wide variability present in most species, has created difficulties in efforts to unambiguously identify the different species. Various DNA isolation protocols were tested in order to determine the most effective methods for isolation of DNA from 22 taxa of Rhododendron for subsequent PCR amplification. DNA yields from the various isolation methods varied widely. A minimum of 50 ng/μL of template DNA was necessary for PCR amplification under standard amplification conditions. Results indicated that the effect of tissue age on the efficiency of DNA isolation was taxa-dependent. For most species, extraction of DNA from freshly harvested young leaf tissue resulted in the highest DNA yields. However, DNA yields from R. serrulatum, R. atlanticum, and R. viscosum `Lemon Drop' were highest when mature leaf tissue was used. Primers designed to amplify the internal transcribed spacer (ITS) region of the nuclear ribosomal genes and the psbD, trnK, and 16S chloroplast genes were tested in various PCR reaction mixes in order to optimize reaction conditions for amplification. Primers to both the ITS and the psbD gene resulted in satisfactory amplification in the presence of 1.5 mM MgCl2 and 50 ng template DNA.

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