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Small heat shock proteins (sHSP) are a specific group of highly conserved proteins produced in almost all living organisms under heat stress. These sHSP have been shown to help prevent damage at the biomolecular level in plants. One of the greatest impediments to production of marketable herbaceous plants and their longevity is high temperature stress. The objectives of this experiment were to study the plant responses in terms of sHSP synthesis, single leaf net photosynthesis, total water-soluble carbohydrates (WSC), and overall growth for two S. splendens cultivars differing in performance under heat stress. `Vista Red' (heat tolerant) and `Sizzler Red' (heat sensitive) were exposed to short duration (3 hours) high temperature stresses of 30, 35, and 40 °C in growth chambers. Increasing the temperature to about 10 to 15 °C above the optimal growth temperature (25 °C, control) induced the synthesis of sHSP 27 in S. splendens. Expression of these proteins was significantly greater in the heat-tolerant vs. the heat-sensitive cultivar. Soluble carbohydrate content was greater in `Vista Red', and in both the cultivars raffinose was the primary soluble carbohydrate in heat-stressed plants. Overall growth of plants was significantly different in the two cultivars studied in terms of plant height, stem thickness, number of days to flower, and marketable quality. The better performance of `Vista Red' under heat stress was attributed to its morphological characteristics, including short stature, thicker stems and leaves. sHSPs and WSC are also found to be associated with heat tolerance and heat adaptation in S. splendens.
One of the greatest impediments to the production of marketable ornamental herbaceous plants in the southern U.S. is high temperature stress. Exposure of plants to sublethal temperature (heat preconditioning) prior to sustained heat stress helps some plants to tolerate subsequent heat stress, a phenomenon often referred as acquired thermotolerance. The objective of this experiment was to examine various morphological, physiological, and anatomical responses of two red varieties of each of the `Vista' (heat tolerant) and `Sizzler' (heat sensitive) series of Salvia splendens to heat preconditioning (HC) and subsequent heat stress treatments [challenging temperatures (CT)]. Cultivars of salvia were subjected to short duration (3 hours) HC of 35 °C every third day until 5 weeks after germination and subsequent exposure to two CT treatments: 30/23 °C and 35/28 °C (day/night) cycles in growth chambers until flowering. Plant growth, marketable quality, stomatal conductance and net photosynthesis declined for `Sizzler' without HC treatment. Compared with nonpreconditioned plants, heat-preconditioned `Sizzler' had 38.28% higher root dry weight, 95% greater leaf thickness, and 50% higher marketable quality at 35/28 °C heat stress condition. Heat preconditioning helped both `Vista' and `Sizzler' to survive in both the heat stress treatments. `Vista' had greater heat-tolerant traits than `Sizzler'; these traits were enhanced with heat preconditioning treatment. The results demonstrated that heat preconditioning enhanced heat tolerance in varieties of salvia, which could be related to heat-tolerant traits, such as dense plant growth with shorter internodes, thicker stems, greater stomatal conductance, and extensive root growth that compensated for the transpiration water loss and cooling effect.
The genus Clerodendrum is of interest to the floriculture industry as a woody, flowering pot plant because of its variation in type of foliage and flowers, production of many inflorescences on one plant, continuous bloom, fast growing and short production cycle. Plant height, however, needs to be successfully controlled to produce a marketable plant. Paclobutrazol (Bonzi) and ancymidol (A-Rest) have been shown to reduce plant growth and increase the number of flowers of C. thomsoniae. The remaining species are relatively new to the floriculture industry and very little information is available on use of growth retardants. Determination of the proper timing, number of applications and rates of growth retardants were studied. Paclobutrazol and ancymidol were applied either as a spray at 0, 100 or 200 ppm, or as a drench at 0, 0.5 or 1.0 a.i./pot to C. thomsoniae, C. ugandense, and C. bungii. Applications began three weeks after rooted cuttings were potted for three consecutive weeks, with randomized plants treated either in week one, two or three with all treatment rates. As in previous studies, C. thomsoniae responded to paclobutrazol and ancymidol by producing a marketable plant, while plant height of C. ugandense and C. bungii was not affected by treatments.
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.
Current recommendations for sufficiency of nutrients in soil-less media for container grown nursery crops have been based on weak acid extraction and pour through sampling of media. Since the concentration of nutrients found in pour through samples are similar to those available in the media solution, sufficiency levels as determined by hydroponics studies have also been considered to be applicable to plants grown in a solid medium such as pine bark. Many variables, however, may affect nutrient availability in a solid medium which are not the same as those in a well-stirred hydroponics system. Objectives of this experiment were to compare growth and nutrient uptake patterns of Euonymous kiautschovica `Manhattan' and Prunus persica `Jefferson' grown in a pine bark/sand medium or a hydroponics system. Quantitative growth characteristics, depletion rates of nutrients in solution, concentration of ions in pour through samples, and tissue levels of N, P, K, Ca, and Mg will be reported.
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.
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.
The majority of Hippeastrum bulbs sold in the U.S. market are shipped from other countries. The shipping time and temperature varies by the country that the bulbs are shipped from and the storage time and temperature also varies by the company that packages the bulbs for retail sale. These packaged bulbs then sit on a shelf until they are purchased and forced by the consumer. These various storage times and temperatures can affect the longevity after packaging (premature emergence) and quality of the finished plant. The objectives of this research were to determine the effects of various storage temperatures and durations on emergence and forcing of Hippeastrum hybrids. Bulbs were stored at temperatures of 5, 9, 13, 21, and 29 °C for 6, 9, 12, and 15 weeks after which time one set was stored at 21 °C (packaged display temperature) and the other set forced in the greenhouse. Emergence of leaves and buds when stored at the 21 °C display temperature and during greenhouse forcing varied by specific hybrid according to storage duration at 5, 9 and 13 °C. Storage at 21 and 29 °C resulted in only leaf emergence and no flower bud emergence during the 21 °C display temperature and greenhouse forcing. Storage at 5 and 9 °C generally resulted in slower leaf emergence and quicker bud emergence. Results from this research can be used to help determine the best storage times and temperatures for preventing premature emergence of Hippeastrum based upon previous shipping times and temperatures.
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.