Jeff S. Kuehny
Jeff S. Kuehny and Patricia Branch
Lateral branches of poinsettia tend to break from the main stem as plants reach maturity. The cause of poor stem strength is not known; however, suggested factors implicated in poor stem strength are: rate of nitrogen fertilizer used, type of plant growth regulator used, crowding of plants, or stem diameter of the cutting. Four different experiments were conducted to determine if these factors affected stem strength of poinsettia. Experiment 1: `Freedom Red', `Success', `V-17 Angelika Red', `Red Sails', `Nutcracker Red', `Cortez', `Maren', and `Red Splendor' poinsettia were fertilized with 20N–1P0–20K at 75, 75/125, 125/200, or 200 ppm N drip fertigation with zero leachate. Experiment 2: Three plant growth regulators were applied to `Pearl' and `Jolly Red' poinsettias. Experiment 3: `Freedom Red' plants were grown in a 625, 900, 1225, or 1600 cm2 area. Experiment 4: Rooted `Freedom Red' cuttings with stem diameters of 4.5, 5.5, 6.5, or 7.5 mm were used. A force meter was used to determine the strength of each lateral on the main stem of the six replications in each experiment. The lower laterals had the least stem strength and the top lateral had the highest stem strength for all treatments in all experiments. The stem strengths of some cultivars in experiment 1 were stronger at the lower fertilizer rates. Type of plant growth regulator had no significant affect on most poinsettia cultivars. The stem strengths of poinsettias in experiments 3 and 4 varied according to which lateral was measured.
Seenivasan Natarajan* and Jeff S. Kuehny
The demand for new and/or improved herbaceous annuals and perennials continues to increase, making information on production and viability of these plants a necessity. In Louisiana and the Southern U.S., one of the greatest impediments to production of marketable herbaceous plants and their longevity is high temperature. Herbaceous plants have various stages of vegetative growth and flowering; high temperatures during these developmental stages can have a tremendous impact on plant metabolism, and thus plant growth and development. The goal of this research was to better understand the differences between heat tolerant (HT) and heat sensitive (HS) species and cultivars at various high temperatures in terms of whole plant growth, flowering, photosynthesis, carbohydrate content, electrolyte leakage, chlorophyll content and plant small heat shock proteins (HSP) expression levels. Salvia splendens Vista Series (HT), Sizzler series (HS); Viola witrokiana `Crystal Bowl Purple' (HT), `Majestic Giant Red Blotch' (HS), F1 Nature Series (HT) and F1 Iona Series (HS); Gaillardia × grandiflora `Goblin' (HT) and Coreopsis grandiflora `Early Sunrise' (HS) were grown from seed in growth chambers under 25/18 °C (day/night) cycles. Plants at 4, 6, and 8 weeks after germination were subjected to different high temperature treatments of 25 (control), 30, 35, 40, and 45 °C for 3 h. Results show that there was a significant difference in net photosynthesis, electrolyte leakage, soluble carbohydrate content and HSP levels between HT and HS cultivars. Effects of high temperature on plant growth, chlorophyll content, and number of days to flower, flower size, and marketable quality were also significantly different.
Seenivasan Natarajan and Jeff S. Kuehny
Many bedding plant cultivars struggle to survive in high temperatures during production. The objective of this research was to study how heat stress and preconditioning affects growth, physiology, and anatomy of the annual bedding plant Salvia splendens Ker Gawl. Heat preconditioning increased the quality and survival capacity of nonheat-tolerant ‘Sizzler Red’. Heat-tolerant traits of ‘Vista Red’ were enhanced with preconditioning. The higher tolerance levels with and without heat preconditioning for ‘Vista Red’ suggested that cultivars with thicker, broader leaves, and higher stomatal frequency had higher light interception, gas exchange, transpirational cooling, and CO2 fixation. These plants attained a more rapid canopy cover and maintained healthier leaves and supplied photoassimilates to reproductive development and root growth. Selecting for these characteristics could be used to help provide guidelines for breeding and selection of heat-tolerant salvia.
Mauricio J. Sarmiento and Jeff S. Kuehny
Rhizomes of Curcuma alismatifolia Roxb. `Chiang Mai Pink', C. gracillima Roxb. `Violet', and C. thorelii Roxb. were soaked in gibberellin (GA4+7) at 0, 200, 400, or 600 mg·L-1 (ppm) and planted into 15.2-cm-diameter (6 inches) containers. The plants were grown in a greenhouse at 30 °C day/23 °C night (86.0/73.4 °F) temperatures. When shoot height was 10 cm (3.9 inches), the plants were drenched with 118 mL (3.9 fl oz) of paclobutrazol at 0, 2, 3, or 4 mg a.i. per 15.2-cm-diameter container. Gibberellin4+7 delayed shoot emergence and fl owering but did not affect the fl ower number. Paclobutrazol rates were not effective in controlling height of C. alismatifolia `Chiang Mai Pink' averaging 85 cm (33.5 inches), C. gracillima `Violet' averaging 25 cm (9.8 inches), or C. thorelii averaging 17 cm (6.7 inches). Curcuma alismatifolia `Chiang Mai Pink', C. gracillima `Violet', and C. thorelii had postproduction longevities of 4.6, 2.6 and 3.8 weeks respectively, making these three species of curcuma excellent candidates for use as fl owering pot plants.
Mauricio J. Sarmiento and Jeff S. Kuehny
Rhizomes of Curcuma alismatifolia `Chiang Mai Pink' and tissue cultured plants of C. cordata, C. petiolata `Emperor', C. thorelii, Kaempferia sp. `Grande', Siphonichilus decora and S. kirkii were grown in a greenhouse under 8-, 12-, 16-, and 20-hour photoperiods. All plants grown under the 8-hour photoperiod became dormant over a 15 week time period. After 90 days, most ginger species grown under the 16- and 20-hour photoperiods were taller than those grown under 8 and 12 hours. A larger number of unfolded leaves was indicated for all ginger species grown under 16- and 20-hour photoperiods compared to those grown under 8- and 12-hour photoperiods except for C. thorelli. The percentage of unfolded leaves as determined by quartile indicated similar results. The number of underground rhizomes of C. alismatifolia, C. cordata, and C. petiolata increased when plants were grown at 16 and 20-hour photoperiods. The number of tuberous-roots (t-roots) increased as photoperiod decreased below 16 hours for C. alismatifolia, C. cordata, C. petiolata, Kaempferia sp. and S. kirkii. Siphonichilus decora produced no t-roots while C. thorelii produced the most t-roots at 16 hours. Vegetative growth of gingers grown in this study, except for C. thorelii, was maintained and increased at photoperiods of 16 and 20 hours.
Photoperiods of 8 and 12 hours induced dormancy and t-root production of most of these gingers.
Jeff S. Kuehny and Mary C. Halbrooks
Research defining actual changes in weight gain of roots and shoots during growth episodes of woody ornamentals is limited. The objective of this study was to develop a better understanding of the patterns of root and shoot growth, nitrogen uptake, and changes in carbohydrate and protein content of Ligustrum japonicum, an episodic species. Shoot elongation and lateral root formation were synchronous. The greatest increase in shoot percent of whole plant fresh weight occurred after shoot elongation however, and the greatest increase in root percent of whole plant fresh weight occurred during shoot elongation. Nitrate uptake was highest during shoot elongation and lateral root formation. Carbohydrate and protein content also varied with each episode of growth.
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.
Mauricio José Sarmiento and Jeff S. Kuehny
Gingers are tropical perennials from the Zingiberaceae family with attractive long-lived flowers that can be grown as potted plants in subtropical and temperate zones under protected conditions. Development of production practices for this new flowering pot crop is essential for optimum plant growth. The effect of photoperiod on growth and flowering was evaluated on Curcuma gracillima, C. cordata, C. alismatifolia, C. petiolata `Emperor', Curcuma `Chang Mai dwarf', Siphonichilus decora, and S. kirkii. Plants were grown under daylengths of 8, 12, 16, and 20 h. Plant height, number of new leaves, number of shoots, and leaf area were larger for plants growing under an extended daylength (16- and 20-h photo-period) than for plants under 8 and 12 h. Plants grown under an 8-h daylength approached dormancy sooner than those growing under 12, 16, or 20 h of light, and no flowering occurred.
Jeff S. Kuehny and Mary C. Halbrooks
Episodic growth is a term used to define alternate episodes of root and shoot growth. Fresh weight gain of Ligustrum japonicum roots and shoots was continuous through each episode of shoot elongation. Root:shoot ratio, however varied over time and oscillated with each episode of shoot elongation. During shoot elongation the percent fresh weight (of whole plant weight) allocated to the shoot decreased while the percent allocated to roots increased. During cessation of shoot elongation the percent fresh weight allocated to the shoot increased; while percent allocated to roots decreased. Formation of lateral roots was synchronous with shoot elongation.