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Peggy Damann and Robert E. Lyons

Chrysanthemum × superbum, Coreopsis lanceolata, and Coreopsis grandiflora are LD flowering perennial plants. The end of juvenility could be defined as the minimum expanded leaf number required for fastest flowering once placed in LD. This research was conducted to compare juvenility and flowering requirements in dwarf and standard cultivars of these species. Plants were maintained under SD and transferred to LD upon reaching true leaf stages beginning with 0 (cotyledons only) and progressing at 2 or 3 leaf intervals to the 24 leaf stage. Coreopsis `Sunray' and Chrysanthemum `G. Marconi' were relatively unresponsive to LD whereas LD induced flowering in 70-100% of the plants in each leaf number treatment in Coreopsis `Early Sunrise'. Plants transferred at the 15 leaf stage required the least number of LD to reach anthesis. LD promoted complete flowering in Chrysanthemum × superbum `Snow Lady' plants and 90% of the SD control plants flowered as well. SD control plants from the other 3 cultivars remained vegetative. Effects of vernalization will also be presented.

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Pamela C. Korczynski, Joanne Logan and James E. Faust

The daily light integral (DLI) is a measurement of the total amount of photosynthetically active radiation delivered over a 24-hour period and is an important factor influencing plant growth over weeks and months. Contour maps were developed to demonstrate the mean DLI for each month of the year across the contiguous United States. The maps are based on 30 years of solar radiation data for 216 sites compiled and reported by the National Renewable Energy Lab in radiometric units (watt-hours per m-2·d-1, from 300 to 3,000 nm) that we converted to quantum units (mol·m-2·d-1, 400 to 700 nm). The mean DLI ranges from 5 to 10 mol·m-2·d-1 across the northern U.S. in December to 55 to 60 mol·m-2·d-1 in the southwestern U.S. in May through July. From October through February, the differences in DLI primarily occur between the northern and southern U.S., while from May through August the differences in DLI primarily occur between the eastern and western U.S. The DLI changes rapidly during the months before and after the vernal and autumnal equinoxes, e.g., increasing by more than 60% from February to April in many locations. The contour maps provide a means of estimating the typical DLI received across the U.S. throughout the year.

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Neil O. Anderson

The increasing number of crops being grown for the floriculture market has frustrated educators faced with limited classroom and laboratory time. Time constraints necessitate selection of crops to serve as examples of floral induction treatment(s) and provide an accurate scope of production requirements for all cultivated species. Since flowers are the primary reason for purchasing most floricultural products—with the notable exception of cut and potted foliage—the various treatments required for flower bud initiation and development were used to categorize potted plants. New and old crops (>70 species) are categorized for flower bud initiation and development requirements, including photoperiod (short, long day, day neutral; facultative/obligate responses), vernalization, temperature, autonomous, rest period, and dormancy. Crop-specific temperature, irradiance, and photoperiod interactions are noted, as well as temperature × photoperiod interactions. A course syllabus can be modified to ensure that at least one crop from each category is presented to serve as a model. It is recommended that the class focuses on example crop(s) from each floral induction category and then reviews other crops within each category for differences or similarities. This method allows coverage of floral induction categories without leaving information gaps in the students' understanding. This method was used with students in the Fall 1999, floriculture production class (Hort 4051) at the University of Minnesota, St. Paul.

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John Erwin, Esther Gesick, Ben Dill and Charles Rohwer

A study was conducted to determine if photoperiod, irradiance, and/or a cool temperatures impacted flowering of selected species in five cactus genera. Gymnocalycium, Rebutia, Lobivia, and Sulcorebutia plants were grown for 4 months under natural daylight conditions (August–November) in a greenhouse maintained at 26 ± 2 °C. Plants were then placed in either of two greenhouses: 1) a greenhouse maintained at 22 °C day/18 ± 1 °C night temperature with an 8-h daylength (SD) or natural daylight plus night interruption lighting (NI; 2200–0200 HR), or 2) a greenhouse maintained at 5 ± 2 °C under natural daylight conditions (8–10 h). After 12 weeks at 5 °C, plants were moved to the SD and NI lighting treatments in the before mentioned greenhouse and additional lighting treatment [natural daylight plus supplemental high-pressure sodium lighting (85–95 μmol·m-2·s-1; 0800–0200 HR)]. In all cases, plants were moved out of lighting treatments after 6 weeks and were then grown under natural daylight conditions in a greenhouse maintained at constant 22 ± 1 °C. Data were collected on the approximate date growth commenced, the date when each flower opened (five flowers only), flower number per plant, and individual flower longevity (five flowers only). Species were classified into photoperiodic and irradiance response groups where appropriate and whether species exhibited a vernalization requirement was reported. Lastly, whether dormancy occurred and what conditions overcame that dormancy was reported.

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Jolene Wright, Ann Reilley, Jean Labriola, Stephanie Kut and Thomas Orton

An experiment was conducted to determine the types, extent, and heritability of new phenotypic variants recovered from carrot cell cultures initiated from mature tap-root explants of the male-fertile carrot (Daucus carota L.) `Slendero'. Embryogenic callus was transferred to plant-growth-regulator-free medium 66 days after culture initiation, and regenerated plantlets were harvested and eventually planted in a field. The tap roots of mature regenerated plants were vernalized at 5C for 9 weeks and replanted. Of 31 flowering regenerants, 25 exhibited some form of petaloid male sterility; the remaining six regenerants were male fertile. All plants from the same original explant were either all sterile or all fertile. Three generations of sterile regenerant × petaloid cytoplasmic male sterility (CMS) maintainer (M) progeny tests showed that the new CMS behaved in a similar manner to that previously reported. Comparison of mitochondrial DNA restriction patterns of sterile and fertile regenerants with those of `Slendero', petaloid CMS, petaloid M, and brown anther CMS lines resulted in the following conclusions: 1) the sterile regenerants exhibited patterns identical to the known petaloid CMS and 2) the fertile regenerants were different from the original `Slendero' and the sterile regenerants and nearly identical to a known petaloid CMS M line. The high frequency of CMS among regenerants from `Slendero' carrot cell cultures may provide an efficient method to develop sterile M tandem lines and corresponding new hybrid varieties.

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David Tay*

In plant germplasm conservation, “orthodox” seed (i.e. seed that survives drying down to low moisture content) is the most suitable propagule for long-term storage. In general, high quality seeds of around 5% seed moisture content can be stored for 5-15 years at 2°C and 15-50 years at -18°C. Globally, there are some 1,300 genebanks and 6.1 million accessions of food and industrial crops in conservation. When collecting and conserving plant germplasm, seed science and technology have to be applied during germplasm collection; seed regeneration-germination, seedling establishment, flower synchronization, pollination, harvesting, drying, processing and packaging; seed storage and conservation; characterization and evaluation; and finally, distribution. Some of the seed science knowledge and technology skills encompass seed sampling strategy, sample size, seed health, germination and vigor testing, dormancy breaking, scarification, stratification, vernalization, photoperiod treatment, isolation and pollination techniques, harvesting, threshing, drying, hermetic packaging, storage facility design, etc. The goal is to produce seed lots that fulfill the required genetic, physical, physiological and health quality. A summary was presented to relate germplasm conservation activities to seed science and technology. Some of the seed production, processing and testing equipment used were highlighted. Seed research in germplasm conservation is therefore crucial to streamline the operation and management of a genebank to make it more cost effective and attractive for funding.

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J. Heinrich Lieth, Deborah Giraud, Glen Forister, Paul Fisher and Loren Oki

Easter lily bulbs are harvested in fields in northern California and southern Oregon, packed in cases, and shipped to distributors and growers. The greenhouse forcer then cools the bulbs at 40–45°F for 6 weeks. This cold period is needed to vernalize the bulbs and to assure that the plants will later flower uniformly. Bulbs that have been cooled for longer or shorter lengths of time respond differently. The objective of this study was to determine the optimal storage temperature regime for the bulbs dug during the early part of the 3-week bulb-harvest period. Twelve groups of bulbs at various storage temperature regimes were evaluated as to their performance during greenhouse forcing. The variables that were considered were: 1) bud count, 2) variability of flowering date, 3) earliness of flowering date, 4) variability of Visible Bud date, and 5) variability of final plant height. An index was developed to evaluate the degree to which each variable impacted the production during the forcing phase. We found that the best protocol for bulb growers is to dig the bulbs and then hold them at cool (>45°F) ambient temperatures for a week. Temperatures higher than the high 65°F should be avoided. If the bulbs will be stored just 1 more week, then they can stay at this temperature; otherwise, the bulbs should be cooled down to, and held at, 42 to 45°F.

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I.L. Goldman and J.F. Watson II

A severe dwarf mutant affecting vegetative and reproductive growth arose spontaneously in our red beet (Beta vulgaris L. subsp. vulgaris) breeding nursery and was used in crosses with inbred lines to characterize its inheritance. Segregation data in backcross and F2 generations were collected. Chi-square goodness-of-fit tests did not deviate significantly from the expected ratios for a monogenic character for each genetic background-generation combination. We propose the symbol dw to describe the genetic control of this dwarf phenotype. Greenhouse experiments were conducted to determine whether the mutant was sensitive to exogenous application of gibberellic acid (GA). GA3 and GA4/7 in concentrations of 0 to 1000 ppm were applied to apical meristems during flower stem development in vernalized dwarf plants. Data on flower stem length and leaf length were collected over a 6-week period during reproductive growth. Recovery of wild-type flower stem length was obtained with application of both types of GA. A 30-fold increase in flower stem length over untreated plants was accomplished by GA application. Results of these phenocopy experiments suggest the mutant gene is involved in GA synthesis.

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Jeffery K. Iles and Nancy H. Agnew

Nine herbaceous perennial species were evaluated for use as flowering potted plants for late winter and early spring sales. Plugs of `King Edward' Achillea × Lewisii Ingw. (yarrow), Arabis sturii Mottet. (rockcress), `Alba' Armeria maritima (Mill.) Willd. (common thrift), `New Hybrid' Bergenia cordifolia (Haw.) Sternb. (bergenia), Chrysogonum virgianum L. (goldenstar), `War Bonnet' Dianthus × Allwoodii Hort. Allw. (Allwood pinks), Phlox × chattahoochee L. (Chattahoochee phlox), `Sentimental Blue' Platycodon grandiflorus (Jacq.) A. DC. (balloonflower), and Veronica L. × `Sunny Border Blue' (veronica) were established in 14-cm (0.8-liter) round plastic containers, grown for one season and covered with a thermoblanket for winter. Five plants of each species were transferred to a 21 ± 3C glasshouse for forcing under natural daylengths at six 10-day intervals beginning 1 Dec. 1993. Arabis sturii, Phlox × chattahoochee, Platycodon grandiflorus `Sentimental Blue', and Veronica × `Sunny Border Blue' flowered out of season without supplemental lighting. `Alba' Armeria maritima and Chrysogonum virginianum also flowered; however, their floral displays were less effective. `New Hybrid' Bergenia cordifolia did not flower and `King Edward' Achillea × Lewisii and `War Bonnet' Dianthus × Allwoodii only flowered sporadically, therefore, these perennials are not recommended for forcing out of season using our vernalization method.

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Phillip A. Wadl* and Richard E. Veilleux

In order to facilitate the high throughput transformation required to use Fragaria vesca (wild strawberry) as a tool in genomic research, functional genomics, and gene discovery not only for strawberry but for fruit crops in general, we need to increase its regeneration frequency and transformation efficiency using Agrobacterium. Ten accessions of F. vesca representing a range of germplasm with worldwide distribution were obtained from the USDA National Germplasm Repository, Corvallis, Ore. for use in shoot regeneration experiments. Seed germination with or without vernalization ranged from 0% to 90%. In vitro growth varied for the accessions with five accessions eliminated from further experiments due to poor growth. In preliminary experiments with 125 leaf explants and 40 petiole explants combined representing PI 551573, PI 602923, and F. vesca `Alpine'; 100% of the uncontaminated explants regenerated at least one shoot after 8 weeks on medium supplemented with 1 mg·L-1 1-phenyl-3-(1,2,3-thiadiazol-5-yl) urea (thidiazuron or TDZ) and 0.2 mg·L-1 2,4-dichlorophenoxyacetic acid (2,4-D). In a replicated study of `Alpine' comparing regeneration on the above TDZ/2,4-D medium with control medium [0.25 mg·L-1 indole-3-butyric acid (IBA)/3 mg·L-1 benzyladenine (BA)], regeneration frequency at 6 weeks for leaf or petiole explants on control medium was 8% (n = 180) compared to 27% (n = 210) on the TDZ/2,4-D medium. This optimized shoot regeneration protocol for F. vesca `Alpine' is currently under investigation in transformation experiments with several other accessions and Agrobacterium constructs.