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Yai Ulrich Adegbola and Héctor E. Pérez

present study, we examined the desiccation tolerance of mature, freshly harvested Gaillardia pulchella seeds to gain some perspective on the storage potential of this species. Additionally, we examined responses to aging stress in an attempt to

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Nicholas J. Flax, Christopher J. Currey, James A. Schrader, David Grewell and William R. Graves

Photoperiod and gibberellin induced growth and flowering responses of Gaillardia × grandiflora HortScience 23 584 586 Flax, N.J. Currey, C.J. Schrader, J.A. Grewell, D. Graves, W.R. 2017 Commercial greenhouse growers can produce high-quality bedding plants

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Kathleen M. Bourke and Robert E. Lyons

Gaillardia pulchella is an annual wildflower with ornamental potential native to the South and Southern West part of the U. S. This experiment attempted to further describe the long day (LD) flowering requirement, approximate the length of the juvenility phase, and characterize apical events during floral initiation. Plants were transferred from short day to LD at various leaf numbers and the time to first flower was recorded from the onset of LD. A quadratic response described the data and indicated that a minimum of 19-20 expanded leaves were needed to flower most rapidly (49 days) once placed in LD. Histological results characterizing apical events will also be discussed.

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Mei Yuan, William H. Carlson, Royal D. Heins and Arthur C. Cameron

Most plants have a postgermination juvenile phase in which flower induction will not occur. Some species require a cold period for flower induction and will not respond to the cold treatments during the juvenile phase. We determined juvenile phases of Coreopsis grandiflora `Sunray', Gaillardia grandiflora `Goblin', Heuchera sanguinea `Bressingham', and Rudbeckia fulgida `Goldsturm'. Plants were exposed to 5C for 0, 10, or 15 weeks when Coreopsis had 0, 2, 4, 6, 8, or 10 leaves (>1 cm); Gallardia, 4, 8, 12, or 16 leaves; Heuchera, 8, 12, 16, or 20 leaves; Rudbeckia, 5, 10, 15, or 20 leaves. Plants were grown under a 4-h night interruption lighting (LD) or under a 9-h photoperiod (SD) after cold treatments. Based on time to flower and final leaf count, the juvenility of Coreopsis, Gaillardia, Heuchera, and Rudbeckia ended when they had about 6, 10, 12, and 15 leaves, respectively. Cold treatments were necessary for flower induction of Coreopsis and Heuchera and they increased the flowering percentage of Gaillardia and Rudbeckia. Heuhera was a day-neutral plant, Rudbeckia was on obligate LD plant, and Gaillardia and Coreopsis were quantitative LD plants.

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Melyssa K. Davis and Jeff S. Kuehny

Herbaceous perennials are one of the fastest growing ornamental sectors in the United States. Current production recommendations do not address the effect of environmental factors, such as high temperature, on growth of herbaceous perennials. The focus of this research was to determine how supra-optimal temperatures effect growth and photosynthesis. Plants were exposed to a high temperature of 35 °C and photosynthesis measurements were recorded over a 6-week period at 1100, 1300, and 1500 hr. Results indicate that the time of day the measurements were taken made little difference on rate of photosynthesis and that there was a similar trend in photosynthetic rate over the 6-week period. Photosynthesis decreased as the plants began to flower and then increased until the onset of flower senescence. Plants grown at supraoptimal and optimal conditions had a similar trend and rate of photosynthesis throughout the 6-week period. Plant growth significantly decreased as the duration of high temperature increased for both species; however, Gaillardia was more heat tolerant then Coreopsis.

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Jeffrey G. Norcini, Helen E. Danielson, Sandra B. Wilson, Rick Schoellhorn and Deborah L. Miller

Containerized Gaillardia pulchella Foug. derived from seed of natural populations in east Texas (ET), northeast Florida (NEF), central west Florida (CWF), central east Florida (CEF), and southeast Florida (SEF) were transplanted in early April to field sites located in northwestern, northern central, and southeastern Florida. During the 22-week study, plants were irrigated only during the first 2 weeks after transplanting to aid establishment. Plant growth was assessed by calculating growth indices (GI, a gauge of plant size based on height and width) at first and second flowering peaks, and by recording shoot dry weight at first flowering peak. Growth index varied among ecotypes and sites but ecotype × site was nonsignificant. At 22 weeks, NEF and ET had GIs about 18% larger than CEF or SEF. Plants grew more at the two northern sites than in southeastern Florida, which was probably due to the loamy soils at the northern sites. Averaged over the entire study, visual ratings of vigor, flowering, and quality varied by ecotype; ecotype × site interactions were nonsignificant. All ecotypes except CEF exhibited equally high vigor, flowering, and quality. Plants in southeastern Florida had lower vigor and flowering ratings than those at the two northern sites. Survival varied by ecotype and site, and ecotype × site was significant. Within a site, survival of NEF, SEF, and ET was equally high (83% to 100%). Also, CWF had 100% survival at the two northern sites, yet no CWF plants survived past week 16 in southeastern Florida. There was no short-term home region advantage to necessitate using local G. pulchella ecotypes in residential or commercial landscapes. CEF and CWF performed poorly in southeastern Florida, which was probably related to excessive June rain.

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Genhua Niu and Denise S. Rodriguez

Gaillardia aristata Foug. is a hardy, drought-tolerant perennial found throughout much of the United States. Little information exists on the salt tolerance of this plant when grown in various growing media. A study was conducted to characterize the response of G. aristata to three salinity levels (0.8, 2.0, or 4.0 dS/m) and four growing media: 1) 100% perlite; 2) 1 perlite: 1 Sunshine mix No. 4 (v/v); 3) 100% Sunshine mix No. 4; or 4) 1 Sunshine mix No. 4: 1 composted mulch (v/v). The type of medium influenced the dry weight of roots but not shoots, while salinity significantly influenced the dry weight of both shoots and roots. The dry weight of shoots was higher in plants irrigated with tap water (0.8 dS/m) compared to those irrigated with saline solution at 2.0 or 4.0 dS/m except for those grown in 100% Sunshine mix. The ratio of root to shoot dry weight was not influenced by salinity, but was highest in the plants grown in 100% perlite. Both medium and salinity affected plant height. Elevated salinity reduced plant height. Plants were taller when grown in 100% perlite and in 1 Sunshine mix: 1 composted mulch. However, plants had fewer lateral shoots when grown in 100% perlite or 1 Sunshine mix: 1 composted mulch. Some of the flower buds aborted when grown in 100% Sunshine mix or 1 perlite: 1 Sunshine mix compared to none in plants grown in 100% perlite or 1 Sunshine mix: 1 composted mulch. These results indicate that growth and morphology of G. aristata were affected by not only salinity, but also the type of medium.

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Mei Yuan, William H. Carlson, Royal D. Heins and Arthur C. Cameron

Scheduling crops to flower for specific dates requires a knowledge of the relationship between temperature and time to flower. Our objective was to determine the relationship between temperature and time to flower of four herbaceous perennials. Field-grown, bare-root Coreopsis grandiflora `Sunray', Gaillardia grandiflora `Goblin', Rudbeckia fulgida `Goldsturm', and tissue culture-propagated Chrysanthemum superbum `Snow Cap' were exposed to 5C for 10 weeks. They were grown at 15, 18, 21, 24 or 27C under 4-h night interruption lighting. Time to visible bud (VB) and first flower (FLW) were recorded. Days to VB, days to FLW, and days from VB to FLW decreased as temperature increased. Time to flower at 15C was 70, 64, 96, and 54 days and 24, 39, 48, and 36 days at 27C for Coreopsis, Gaillardia, Rudbeckia, and Chrysanthemum, respectively. The 27C temperature apparently caused devernalization on Coreopsis because only 40% of the plants flowered. The effects of temperature on flower size, flower bud number, and plant height also are presented.

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Mei Yuan, William H. Carlson, Royal D. Heins and Arthur C. Cameron

Scheduling crops to flower on specific dates requires a knowledge of the relationship between temperature and time to flower. Our objective was to quantify the effect of temperature on time to flower and plant appearance of four herbaceous perennials. Field-grown, bare-root Coreopsis grandiflora (Hogg ex Sweet.) `Sunray', Gaillardia ×grandiflora (Van Houtte) `Goblin', and Rudbeckia fulgida (Ait.) `Goldsturm', and tissue culture—propagated Leucanthemum ×superbum (Bergman ex J. Ingram) `Snowcap' plants were exposed to 5 °C for 10 weeks and then grown in greenhouse sections set at 15, 18, 21, 24, or 27 °C under 4-hour night-interruption lighting until plants reached anthesis. Days to visible bud (VB), days to anthesis (FLW), and days from VB to FLW decreased as temperature increased. The rate of progress toward FLW increased linearly with temperature, and base temperatures and degree-days of each developmental stage were calculated. For Coreopsis, Leucanthemum, and Rudbeckia, flower size, flower-bud number, and plant height decreased as temperature increased from 15 to 26 °C.

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Melyssa K. Davis and Jeff S. Kuehny

Coreopsis and Gaillardia were exposed to supra-optimal temperatures of 35 °C for a 6-week period beginning at flower initiation. Photosynthesis measurements were recorded at 1100 hr, 1300 hr, and 1500 hr for 3 days each week and carbohydrate partitioning was determined once per week. Results indicate that the time of day the measurements were taken made little difference on rate of photosynthesis and that there was a similar trend in photosynthetic rate over the 6-week period. Photosynthesis decreased as the plants began to flower and then increased until the onset of flower senescence. The patterns of carbohydrate partitioning were similar to those observed for photosynthesis. The plants grown at supra-optimal and optimal conditions had a similar trend and rate of photosynthesis throughout the 6-week period. Plant growth and total carbohydrates significantly decreased as the duration of high temperature increased for both species, however Gaillardia was more heat tolerant than Coreopsis.