Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 52-53). Also available via the Internet.

Photoperiod studies have been the subject of research projects for decades. In such studies, Rudbeckia hirta L. has often been chosen due to its early recognition (1920?s) as a long day plant. R. hirta has also been the subject of experiments to evaluate the timing of floral initiation in regard to the exogenous application of phytohormones. Former projects have been primarily directed toward understanding floral initiation mechanisms of long day plants for the production of greenhouse grown crops. Photoperiod manipulation and exogenous application of phytohormones have not been used to the same extent for field-grown fresh flower research. Three experiments were conducted in the spring of 2006 to determine if time to flowering could be manipulated for field grown R. hirta without subsequent loss of quality. In the first experiment, two cultivars, R. hirta ?Indian Summer? and R. hirta ?Irish Eyes? were given 4-hour night interruption (NI) using a 60-watt incandescent bulb during greenhouse production. Night interruption lasted for 0, 21, 28 or 35 days. Prior to field transplanting, GA3 was exogenously applied once to transplants at rates of 0, 150 or 300 ppm. For ?Indian Summer?, early flowering was achieved with 35 days of NI alone or with either rate of GA3 plus 21-day NI. Increasing GA3 to 300 ppm improved stem length. For ?Irish Eyes?, 35-day NI alone was equally effective at producing early blooms compared to 35-day NI and either rate of GA3. The second experiment included R. hirta ?Irish Spring? grown in the greenhouse then given 0 or 35 days NI as in the first experiment. Then, seedlings were transplanted to the field in plots with various combinations of polyethylene row cover, black plastic mulch and bare ground. Only plants receiving 35-day NI flowered during the test. Polyethylene row cover increased the percentage of blooms harvested. The third experiment measured the vase life of blooms harvested from experiments one and two. Treatments did not affect vase life of blooms. Mean post harvest life for all treatments was greater than 7 days.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references. Also available via the Internet.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Thesis (M.S.)--Ball State University, 2009. / Title from PDF t.p. (viewed on June 07, 2010). Includes bibliographical references (p. [53]-56).

Rudbeckia hirta is a tender perennial or self-sowing annual which is becoming increasingly popular as a garden flower and a component of wildflower meadow mixes. It may also have -considerable potential for use as a potted crop. R. hirta has a defined juvenility period but preliminary unpublished results suggested that plants originating from different latitudes may possess unequal juvenile periods and exhibit dissimilar sensitivities to photoperiod. Seven R. hirta ecotypes originating from latitudes ranging from 30.l0oN to 45.l0oN were exposed to long days (LD) at different leaf numbers to determine juvenile phase length and speed of floral initiation. Ecotypes from northern latitudes had fewer leaves at maturity and, overall, there was a quadratic relationship between latitude of origin and number of days to first flower from start of LD. Once plants were mature, the speed of floral initiation and development also varied among ecotypes. / Master of Science

Phenological studies of coneflower on aspen range in Northern Utah showed that resumption of growth of mature plants begins at the time of snow melt and the initial or rosette stage is completed between mid-May and mid- June. The rate of growth in this stage is controlled by temperature, being greater at higher mean temperatures. The bolting stage is completed about 1 week after the initiation of stem elongation and the process of capitulum development is begun. Flowering is initiated between late July and mid- August. Cross-pollination is necessary for seed set which is completed by the end of August. Seed dissemination is begun at that time and is completed by the middle of September. Altitude appeared to have an effect on the extent of seed filling, since collections from higher altitudes had lower percentages of filled seeds. Seedling mortality increases as the season advances and reaches a maximum at the end of June when the associated species begin rapid growth. During the first season seedling growth is restricted to one unelongated stem and three leaves. Shoot/root ratios indicated that the main development during this season is in the roots. Optimum controlled conditions for seed germination are alternating temperatures of 25 C-15C with 8 hour photoperiods coinciding with the periods of higher temperature. A constant temperature of 25 C or alternating temperatures of 15 C-5C or constant darkness under any of the temperature regimes give lower germination percentages. Growth chamber studies demonstrated that coneflower is a long day plant since normal development to the seed setting stage is obtained under 18 hour photoperiods but not under 12 hour photoperiods when temperature alternations of 25 C-15 C are used. Low temperature stratification of the crown buds is not required for normal development. A series of field experiments showed that coneflower does not inhibit the growth of an important associated grass species--mountain brome. Laboratory experiments with foliage leachate gave no evidence of inhibitory effects on the germination or growth of other species. Force-feeding of sheep with whole dried plants collected at the seed set stage showed no toxicity for these animals. Total non-structural carbohydrates increase in the aerial parts of the plant as the growing season progressed up to the seed set stage and decreases thereafter until death of the aerial parts. Carbohydrates in the roots show a reverse trend. Two or three clippings applied to the rosette stage resulted in death of the plants. Failure of regrowth after these clippings was probably due to exhaustion of the supply of mature buds on the crown rather than being due to exhaustion of food reserves since significant concentrations of nonstructural carbohydrates were still present in the roots of these dead plants.

We aimed to identify the volatile compounds in inflorescences of Rudbeckia hirta that may be responsible for the olfactory attraction of the crab spider Misumenoides formosipes to this plant. Our approach was to use ultrasonic extraction, separate the extract into fractions using flash chromatography with different solvent systems, and test the attraction of the male spiders to the pooled fractions using a y-tube olfactometer. Ultrasonic extraction is carried out using a mixture of 1:2 hexane/diethyl ether with 10 g of inflorescences for 30 minutes. Bioassay results indicated that male spiders chose the inflorescences, bulk ultrasonic extract, and the pooled 100% dichloromethane fractions over controls. Nuclear magnetic resonance experiments and infrared spectroscopy experiments were carried out on the 100% dichloromethane fractions and these experiments indicated that a long chain hydrocarbon is the main component in the 100% dichloromethane fractions / Chromatographic method and bioassay development method -- M. formosipes olfactory response to R. hirta -- Separation and identification of the possible attractants in the 100% dichloromethane fractions. / Department of Chemistry

Thesis (Ph.D.) -- Mississippi State University. Department of Plant and Soil Sciences. / Title from title screen. Includes bibliographical references.