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  • Author or Editor: Brent H. McCown x
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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.

Open Access

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.

Open Access

Abstract

Low temperature was not a requirement for flowering in ‘Heritage’, a primocane-fruiting red raspberry, as non-cold treated primocanes flowered at about 80 nodes. The amount of growth before flowering was inversely related to the amount of growth before cold exposure. Cold exposure (7°C) for 25 days at the 10-12 or 14-16 nodes stages of growth was followed by flowering at 32 and 28 nodes, respectively. Winter cold exposure until mid-December at the stage of adventitious buds on the root resulted in flowering at 41 nodes. Cold treatment did not influence the number of nodes that developed inflorescences on any one primocane.

Open Access

A project to determine the comparative growth response of micropropagated (MP) and field propagated (FP) cranberry plants was conducted in field plots at a commercial cranberry marsh. Microcuttings were derived from shoot culture and rooted in either plugs or peat pots filled with peat. Replicated 1 m2 plots of MP plants and 15 cm FP cuttings were planted in June. Survival of MP plants after one month was significantly greater than that of the FP plants. Significant growth differences were observed later in the season. The MP plants produced more branches and greater runner elongation, resulting in a much greater ground cover. Many of the FP plants flowered and produced fruit, while the MP plants produced neither. Far fewer new flower buds were set in the fall on the MP plants. Potential advantages of MP cranberries include the fast, uniform establishment of new marshes and consequently earlier achievement of full productivity, and the rapid introduction of new genotypes from breeding or genetic engineering.

Free access

Taxol, a promising anticancer drug, is limited by inadequate supply. The production of taxol and related compounds (taxanes) by Taxus tissue cultures has been reported, yet sustained production has not been demonstrated. One theory is that cell differentiation and/or tissue organization is required to sequester taxol and avoid autotoxicity. To investigate this, T. cuspidata shoot cultures were established and the taxane content of various culture stages compared to that of field needles. HPLC analysis identified two peaks which comigrated and had UV spectra identical to taxol and 10-deacetyl taxol. The levels of 10-deacetyl taxol were similar in all samples. Cultured shoots contained much less taxol than field needles, and the level of a third peak which migrates closely to taxol was inversely related to that of taxol. Taxol content was restored in the first flush out of culture. Shoot cultures of T. brevifolia, T. x media, and T. canadensis have also been analyzed. In addition to shoot cultures, nodule cultures, a biological unit that may be suitable for production of taxanes in plant bioreactors, have been initiated and characterized.

Free access

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.

Free access

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.

Open Access

Abstract

Anatomical and physiological comparisons were made between tissues of Betula platyphylla var. szechuanica (Schneid.) Rehd. (Asian white birch) obtained directly from microcultured shoots, from seedlings grown in a micro-culture-like environment, or from micropropagated plants grown in a greenhouse. The diminished stature of microcultured shoots resulted primarily from reduced cell division, although their leaves had reduced cell size as compared to shoots from greenhouse-grown plants. The area occupied by vascular tissue in midrib veins and petioles was significantly reduced in microcultured shoots as was the extent of the palisade layer, indicating that cell differentiation had also been altered. The photosynthetic capacity of leaves from microcultured shoots was less than half that of leaves from greenhouse-grown plants. However, this capacity was restored after non-in vitro rooting of the microcultured shoots. Unlike greenhouse-grown plants, photosynthetic rates of leaves from microcultured shoots were not influenced by decreasing light intensities from 1200 to 200 μmol·s−1·m−2 nor was the respiration rate strongly inhibited by cyanide. Seedlings from a high-humidity, microculture-like environment generally had characteristics intermediate between those of microcultured and greenhouse-grown tissues, indicating that the environment and not the juvenile state of the tissue was probably of overriding importance in influencing these trends.

Open Access