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Abstract
ASHS has markedly increased emphasis on poster presentations of scientific papers at its Annual Meetings. An attempt will be made by the meeting organizers to have 50% of the contributed papers presented as posters at the 1981 Annual Meeting. Since many of our members have not previously presented papers in this form, a discussion of poster preparation and presentation techniques is appropriate.
The gene encoding β-glucuronidase, GUS, has been inserted into cranberry and is expressed in various tissues. Detectable expression of the GUS gene is enhanced up to 15x when the phenol-adsorbing compound, polyvinylpolypyrrolidone, is included in the extraction buffer of the fluorometric MUG assay, indicating that an endogenous, probably phenolic, compound is inactivating the foreign enzyme. Extracts from in vitro-grown cranberry leaves reduce the activity of purified β-glucuronidase in fluorometric assays. This is in contrast to extracts from other plants which have no affect on the enzyme. Detectable expression of the GUS gene for an individual transclone varies with the age of the tissue and the environment in which the plant is grown. The BT gene, which encodes for the Bacillus thuringiensis δ-endotoxin, was also inserted into cranberry with the purpose of incorporating lepidopteran insect resistance. Bioassays using an important insect pest on cranberry show generally inconsistent feeding patterns on transgenic plants. These results may be due to the interaction of the endogenous compounds and the B.t. δ-endotoxin.
The capability to uniformlyinduce flowering in cranberry (Vaccinium macrocarpon Ait. `Stevens') in < 1 year from microculture was investigated to accelerate cranberry breeding and to study woody plant reproductive biotechnology. Flower buds were induced on newly micropropagated cranberry plants during the first growing season. A treatment of 2.5 mg of paclobutrazol applied as a soil drench per 2- to 3-month-old potted plant in midsummer, when the plants were grown in coldframes under natural daylength and air temperatures, resulted in 70% of the plants flowering. Plants not treated with paclobutrazol did not flower. Reduced but significant flower bud set was observed on plants treated with paclobutrazol but grown in the greenhouse under natural daylength. Flowering was stimulated by cold treatment coupled with gibberellin sprays and/or repotting to nonpaclobutrazol-treated medium. Chemical name used: β -[(4-chlorophenyl)methyl]-ct-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).
Abstract
Stock cultures of 5 cultivars of Episcia, Gesneriaceae, were readily maintained as callus and shoot regeneration was rapid and dependable. Callus initiation was best from 1–2 mm stem tips or 5 × 10 mm leaf sections on Murashige and Skoog (MS) basal medium containing 0.1mg/liter naphthaleneacetic acid (NAA) and 0.5 mg/liter benzyladenine (BA). Cytokinin or auxin concentrations up to 5.0mg/liter did not greatly affect sub-cultured callus growth. Even a medium lacking growth regulators supported rapid callus growth, doubling in size every 4 days. Shoot formation from callus occurred when calli reached about 3g, thus showing a dependency on initial subculture size. Frequent subculturing maintained the callus state. Cytokinin concentration did not affect quantity of shoots produced, however shoot quality was affected. Albino callus from two chimeral cultivars inhibited shoot development more than its green counterpart. Response in culture varied considerably between cultivars. Using certain cultivars, as many as 800,000 Episcia plantlets could be produced annually per square meter of microculture space.
Genetically transformed Vaccinium macrocarpon `Stevens' and `Pilgrim' plants have been obtained using electric discharge particle acceleration. Three foreign genes, kan encoding a selectable marker, gus a reporter gene, and B.t.k. conferring lepidopteran resistance, were incorporated into the genome. Expression of kan was assayed by culturing shoots in vitro on media with several concentrations of kanamycin. Expression among transformed clones (transclones) varied from high resistance (normal growth at 300 mg/L kan) to no resistance. Histochemical analyses for gus expression revealed variability among transclones. Some transclones exhibited no gus expression, others had consistent area-specific expression while others displayed random expression. In preliminary feeding trials with blackheaded fireworm larvae, B.t.k. expression was found to be ineffective at controlling insect development. We have recovered plants transformed with a different promoter driving the B.t.k. gene in an effort to enhance expression.
A significant pest affecting commonly planted Betula spp. is the birch leafminer (Fenusa pusilla Lepeletier), an insect that can be present in large populations in the landscape and can greatly reduce the vigor and ornamental value of these trees. Twenty-two interspecific crosses were performed between leafminer resistant and susceptible Betula species in an attempt to create the novel combination of ornamental white bark and significant leafminer resistance. Of the nine successful crosses, two produced resistant offspring. Progeny of the diploid × hexaploid cross B. turkestanica Litvin (2x) × B. alleghaniensis Britt. (6x) displayed a broad range of resistance levels, likely the result of segregating alleles contributed by the hexaploid parent. All crosses involving highly resistant individuals of B. costata Trautv. (2x) yielded leafminer susceptible progeny. These results suggest that the larval antibiosis demonstrated by B. alleghaniensis and B. costata is inherited as a recessive trait, and exhibits a gene dosage effect as evidenced by the B. turkestanica × B. alleghaniensis offspring. While most progeny of the B. populifolia Marsh (2x) × B. maximowicziana Regal (2x) cross were susceptible, a single resistant offspring, which was found to be triploid (3x), displayed a mechanism of resistance similar to that of a hypersensitive response. No strong intersectional barriers to hybridization were observed and all interploidy crosses were successful. The chromosome numbers of B. costata (2n = 2x = 28) and B. turkestanica (2n = 2x = 28) are reported here for the first time. The results of this study indicate that the potential exists for the development of insect resistant, ornamental white-barked birch clones through the implementation of a planned, systematic breeding program.
Abstract
A shoot-tip necrosis in actively-growing shoot cultures of various species has been observed. Using 3 cultivars of Solatium tuberosum grown on media differing in Ca concentration (0.3, 3.0, and 30 mm Ca), typical necrosis was induced or suppressed. Potatoes at 0.3 mm contained about 0.1% Ca g1 dry weight of shoot and also showed the highest incidence of shoot-tip necrosis, ranging from 48% to 72%, depending on the cultivar. Potatoes grown at 3 or 30 mm Ca contained 0.5% or 3% Ca g−1 dry weight of shoot, respectively, and showed only 0% to 9% necrotic shoots, depending on cultivar. In addition to medium Ca content, Parafilm used as the vessel closure promoted shoot-tip necrosis, but increased levels of Ca in the medium tended to overcome the effect. Although cultivar differences in tissue content of other minerals were apparent, these were not associated with the shoot-tip necrosis problem. We conclude that shoot-tip necrosis is associated with a Ca deficiency in actively-growing shoot cultures.