Date of Award

5-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Plant and Environmental Science

Advisor

Faust, James Brown

Committee Member

White , Sarah

Committee Member

Adelberg , Jeffrey

Committee Member

Bridges , William

Abstract

Fuel-efficient poinsettia production has become an important topic in recent years due to increased fuel costs while wholesale prices have remained relatively unchanged. Fuel-efficient production results in energy saving, reduces costs associated with production and improves profitability of the poinsettia crop. Experiments were carried out to determine the effects of Fascination (a plant growth regulator), production temperature, light, and cold pre-harvest temperature on bract expansion, cyathia development, and retention for fuel-efficient poinsettia production.
The first experiment (Chapter 2) examined the effects of the plant growth regulator Fascination on bract expansion of poinsettias grown at relatively cool production temperatures. Poinsettia, (Euphorbia pulcherrima Willd. Ex Klotzsh), `Freedom Early Red' and `Prestige Early' plants were grown until first color was observed on the developing bracts and then moved to each of two different greenhouses with average daily temperatures of 15.5 ±0.33 or 18.0 ±0.74 ¡C. Fascination is a commercial plant growth regulator that contains a 1:1 ratio of the gibberellins (GA4+7) and cytokinin (benzyladenine). Fascination was applied as a 5 or 10 ppm spray, and the applications were made either 2, 3, or 4 weeks after first color. Fascination improved bract size at 18 ¡C for `Freedom Early Red' but not for `Prestige Red'. Fascination increased plant height at 15.5 and 18 ¡C for both cultivars. Therefore, Fascination has the potential to increase bract size of `Freedom Early Red' poinsettias that have been grown at 15.5 ¡C; however, temperature will need to be increased to 18 ¡C to attain marketable bract size.
The second project (Chapter 3) included three experiments to determine the effect of temperature and light on poinsettia cyathia development. In the first experiment, `Prestige Red' plants were grown at 18, 20, or 22 ¡C and three different shade levels (0, 50 or 75%) resulting in average daily light integrals (DLI) of 4.2, 2.1, or 1.1 mol.m-2.d-1, respectively, from the start of short days. The results showed that cyathia development increased as temperature or light increased. At 22 ¡C and 0% shade treatment, 70% of the shoots had cyathia that reached the nectar stage, while no shoots reached the nectar stage at 18 or 20 ¡C. No cyathia development occurred at 18 ¡C, regardless of light level. Similarly, no more than 10% of the shoots displayed cyathia development at 75% shade, regardless of temperature. In the second experiment, `Prestige Red' plants were grown from the start of short days at 20 ¡C and under one of three daily light integral (DLI) treatments (0, 50 or 75% shade). The plants were moved between shade curtain treatments (0, 50 or 75%) at different dates in order to create nine different DLI treatments. The DLI treatments that had cumulative light levels of 42.9 to 56.1 molm 2.d 1 during the two weeks preceding data collection successfully developed to the nectary gland stage. In contrast, DLI treatments that had cumulative light levels from 14.0 to 28.1 mol m-2.d-1 during the two weeks preceding data collection did not develop to the nectary gland stage. The 0% shade treatments had the largest cyathia at visible bud and were the only treatments that developed to the nectary gland stage. In the third experiment, five poinsettia cultivars (`Advent Red', `Early Freedom Red', `Jubilee Red', `Prestige Red', and `Prestige Early Red') were moved at the start of visible bud to different greenhouses that had average daily set point temperatures of 15.5, 18, 20, or 22 ¡C. None of the cultivars reached the visible bud stage at 15.5 ¡C. Cyathia diameter increased as temperature increased from 18 to 22 ¡C. The rate of bud expansion was similar for plants grown at 20 and 22 ¼C, but was slower at 18 ¡C. The time from visible bud to anthesis increased as temperature decreased, e.g., time from visible bud to anthesis took 15 days at 22 ¡C, 20 days at 20 ¡C and 25 days at 18 ¡C.
The third experiment (Chapter 4) examined the effect of pre-harvest temperatures on post-harvest longevity of flowering. Five poinsettia cultivars were grown at standard greenhouse production temperatures until anthesis of the primary cyathium. The plants were then moved to a greenhouse with 13 ¡C day and 9 ¡C night temperatures for 0, 1, 2, 3, or 4 weeks before they were placed into a simulated post-harvest environment consisting of average temperatures of 21 ¡C and a DLI of 0.5 mol m-2d-1. The dates of cyathia abscission were recorded for the primary and secondary cyathia. The best postharvest performance was observed on `Polar Bear', where the primary cyathia lasted for 24, 23, 20, 19 or 17 days on plants held in the cold greenhouse for 0, 1, 2, 3 or 4 weeks, respectively, while the secondary cyathia lasted for 29, 25, 20, 19 and 17 days, respectively. The poorest postharvest performance was observed for `Prestige Red', where the primary cyathium lasted for 12, 6, 3, or 0 days when held in the cold greenhouse for 0, 1, 2, 3, or 4 weeks, respectively. Assuming that 14 days of secondary cyathia retention in the postharvest environment is considered to be acceptable, `Advent Red' and `Polar Bear' met this criterion following four weeks of pre-harvest, cold temperatures. `Polly's Pink' met this criterion following one week of cold pre-harvest temperature. `Prestige Red' and `Freedom Early Red' did not meet this criterion even when no cold pre-harvest environment was provided.
In conclusion, our first experiment, Fascination application rate of 10 ppm resulted in a significant increase in bract area for `Freedom Early Red' if the application date was relatively late in bract development, e.g., 3 to 4 weeks after first color, and the air temperature was sufficiently warm, e.g., 18 ¡C. For `Prestige Red', the trend was that bract area increased at 18 ¡C and 10 ppm Fascination; however these treatments were not statistically different from the control. Increases in `Freedom Early Red' height were observed with the Fascination treatments that also positively increased bract area. Our results showed that Fascination can be used for fuel-efficient poinsettia production to increase plant height and bract expansion when the plants have experienced reduced bract size due to low temperature production. However, the efficacy of the application decreases at 15.5 ¡C, the greenhouse temperatures should be increased to allow for a more effective response to Fascination.
In the second experiment, cyathia development increased as temperature or light increased. At 22 ¡C and 0% shade treatment, 70% of the shoots had cyathia that reached the nectar stage, while no shoots reached the nectar stage at 18 or 20 ¡C. No cyathia development occurred at 18 ¡C, regardless of light level. Similarly, no more than 10% of the shoots displayed cyathia development at 75% shade, regardless of temperature. The DLI treatments that had cumulative light levels of 42.9 to 56.1 mol.m-2.d-1 during the two weeks preceding data collection successfully developed to the nectary gland stage. In contrast, DLI treatments that had cumulative light levels from 14.0 to 28.1 mol m-2.d-1 during the two weeks preceding data collection did not develop to the nectary gland stage. The 0% shade treatments had the largest cyathia at visible bud and were the only treatments that developed to the nectary gland stage. Cyathia diameter increased as temperature increased from 18 to 22 ¡C. The rate of bud expansion was similar for plants grown at 20 and 22 ¼C, but was slower at 18 ¡C. The time from visible bud to anthesis increased as temperature decreased, e.g., time from visible bud to anthesis took 15 days at 22 ¡C, 20 days at 20 ¡C and 25 days at 18 ¡C.
In the third experiment, our research showed that following 2 to 4 weeks of exposing poinsettias to the cold pre-harvest treatment only two cultivars (`Polar Bear' and `Advent') had secondary cyathia that persisted for 14 days in the postharvest environment. In contrast, `Prestige Red', `Polly's Pink' and `Freedom Early Red' performed relatively poorly in the postharvest environment. Demonstrating that cold pre-harvest treatment performance is cultivar-dependent. In conclusion, cold pre-harvest treatment is a potentially useful commercial technique in cultivars that have strong cyathia development and retention.

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