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Pepper cultivars differ in susceptibility to stress-induced bud abscission. The stress susceptible cultivar `Shamrock' undergoes a larger reduction in net assimilation rate (NAR) under low light stress, and partitions less dry matter (DM) to reproductive structures than the more tolerant cultivar `Ace'. To determine if photosynthetic rates under low light stress could explain NAR differences, photosynthesis was measured on `Ace' and `Shamrock'. Assimilate partitioning was compared through measurement of leaf and bud respiration rates and analysis of bud sugar concentrations. Cultivar photosynthetic rates of exposed leaves did not differ under low light. Bud respiration rates fell to a lower level in `Shamrock' than `Ace' in low light-stressed plants, while expanded leaves respired at higher rates in `Shamrock' than `Ace' under both full and low light. Bud sugar concentrations were significantly lower in `Shamrock' than `Ace' after 3 days of low light stress. Susceptibility to low light stress-induced bud abscission in `Shamrock' appears to be associated with reduced assimilate partitioning to buds, perhaps caused by high assimilate consumption in maintenance of expanded leaves.

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Abstract

Two experiments were conducted to test the hypothesis that plants in the vegetative state would not succumb as rapidly to low light intensities if they had no phosphorous available as the resulting restriction in growth would permit stored photosynthate to be available for plant maintenance. The first used Peperomia obtusifolia ‘Variegata’ as the test plant. The rooted cuttings were received on December 22, 1965, and potted in propagator’s sand. They were grown in sand cultures to the surface of which a mineral nutrient solution was applied daily with the leachate allowed to drain away. The mineral nutrient solution contained in millimoles per liter, 5, 6, 1, and 1 of Ca(NO3)2, KNO3, KH2PO4, and Mg-SO4, respectively. Two ppm of Fe were added as a chelate (Fe 138) and trace elements were added as usual for a solution culture according to the recipe of Hoagland.

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acceleration in the reproductive mode of plants grown at either 100 or 175 mol·m −3 NaCl. In this experiment, no difference in flowering was observed at low concentrations of seawater salt spray whereas decreased flowering occurred at higher concentrations of

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There is an increasing need to recirculate and reuse nutrient solutions to reduce environmental and economic costs. However, one of the weakest points in hydroponics is the lack of information on managing the nutrient solution. Many growers and research scientists dump out nutrient solutions and refill at weekly intervals. Some authors have recommended measuring the concentrations of individual nutrients in solution as a key to nutrient control and maintenance. Dumping and replacing solution is unnecessary. Monitoring ions in solution is unnecessary; in fact the rapid depletion of some nutrients often causes people to add toxic amounts of nutrients to the solution. Monitoring ions in solution is interesting, but it is not the key to effective maintenance. During the past 18 years, we have managed nutrients in closed hydroponic systems according to the principle of “mass balance,” which means that the mass of nutrients is either in solution or in the plants. We add nutrients to the solution depending on what we want the plant to take up. Plants quickly remove their daily ration of some nutrients while other nutrients accumulate in the solution. This means that the concentrations of nitrogen, phosphorous, and potassium can be at low levels in the solution (<0.1 mM) because these nutrients are in the plant where we want them. Maintaining a high concentrations of some nutrients in the solution (especially P, K, and Mn) can result in excessive uptake that can lead to nutrient imbalances.

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Buffalograss [Buchloë dactyloides (Nutt.) Engelm.] is a warm-season perennial grass native to the North American Great Plains region and has been used as a low-maintenance turfgrass. Turf-type buffalograsses are available and are commonly used on nonirrigated land. Our objectives were to determine the deepest planting depth of burrs that would allow acceptable emergence, and to evaluate planting depth effects on buffalograss seedling morphology. Two greenhouse experiments were conducted in Fall 2000. Experimental design was a randomized complete block with 4 replications and a 3 (cultivar) × 6 (planting depth) factorial treatment arrangement. Results showed that buffalograss emergence decreased as planting depth increased. All cultivars had <10% total emergence at planting depths >50 mm. Emergence rate indices were greatest when planting depth was 13 mm and were significantly lower at planting depths of 51 and 76 mm. Average coleoptile length was 11 mm. Coleoptile length was similar between all planting depths except for the 13 mm depth which resulted in 9-mm-long coleoptile. Subcoleoptile internode length increased with planting depth up to 38 mm. Planting depths deeper than 38 mm did not significantly increase subcoleoptile internode length.

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Salt tolerance of landscape plants is important to ornamental growers as well as residents and landscapers in coastal communities. Damage to ornamental plants from salt spray can be prevented by evaluating and selecting plants that exhibit tolerance to aerosol salts. Ornamental grasses are frequently recommended for low-maintenance landscape situations and may be candidates for coastal plantings once they are evaluated for their salt spray tolerance. The objective of this study was to determine the salt spray tolerance of Miscanthus sinensis `Gracillimus' and Pennisetum setaceum `Hamelin'. The experiment was conducted for 90 days from 7 July to 5 Oct. 2005 in a polyethylene greenhouse in Gainesville, Fla. Plants were subjected to four treatments (100% seawater, 50% seawater, 25% seawater, or 100% deionized water) applied by spraying each plant to runoff three times per week. Plant heights, flower number, and aesthetic ratings were recorded biweekly for the duration of the experiment. Root and shoot dry weights were determined at the initiation and completion of the study. Significant growth rate differences were found between treatments. Growth rates of plants treated with 100% seawater were significantly lower than the control and other seawater concentrations. Root and shoot dry weights of the plants treated with 100% seawater were significantly lower than the other treatments. In addition, significant differences were found between the 100% seawater treatment, the 25% seawater treatment, and the control in the aesthetic ratings of plants at the end of the study.

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Abstract

Complete landfills throughout the United States are being developed into parks, golf courses, nature areas, and other multiple-use facilities. A critical element in achieving these end uses is establishment and maintenance of trees on the final cover soil over the refuse layers. Factors that affect establishment include toxicity of landfill-generated gases (e.g., CO2) to root systems, low soil O2 supply, thin cover soil, low water-holding capacity, species sensitivity, and other factors (Flower et al., 1978). Species differ in their tolerance to landfills (Leone et al., 1979). Nyssa sylvatica (Marsh) and Gingko biloba [(L.) Karst] were tolerant of conditions in landfill cover soil, whereas Liquidambar styracifula (L.) was intolerant. This study was designed to determine if plant tolerance to landfill cover soil was related to root system depth.

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Broccoli tissue, ranging in weight from 7 to 21 g, was sealed in packages made from low-density polyethylene (LDPE) of various thickness and permeability to establish a range of O2 levels in the package headspace. A pouch containing either hydrogen peroxide (H2O2) or water as a control was also sealed in the package. For packages that developed anaerobic atmospheres, inclusion of H2O2 permitted the maintenance of aerobic conditions for up to 3 days at ambient room temperature. These results suggest that the plant tissue is able to actively metabolize the H2O2 vapor to generate O2, which will prevent the development of low-O2 conditions in packaged produce, even under conditions of elevated storage temperature.

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Although roses have long been an important landscape plant, there is a growing interest in the use of low-maintenance roses that do not require heavy pruning or spraying. Poulsen Roser Pacific, Inc. of Central Point, Oregon, provided three plants of 48 cultivars for a trial in Stillwater, Oklahoma. The plants were produced in Oregon by grafting cultivars on seedling Rosa multiflora rootstock. Two-year-old plants were shipped bare-root to Stillwater, Oklahoma where they were planted in the field in early April, 2001. The plants were placed in three randomized complete blocks (rows) with 90 cm spacing between plants and 240 cm spacing between rows. The plants were drip irrigated as needed. During the 2002 growing season the roses were evaluated weekly for flower number, black spot, and overall quality. Four rose cultivars from Poulsen's Town and Country® series of landscape roses, Martha's Vineyard™ (`Poulans'), followed by Madison™ (`Poulrijk'), Kent™ (`Poulcov'), and Tumbling Waters™ (`Poultumb'), had the highest average flower number. Martha's Vineyard™, Kent™, and Tumbling Waters™ also rated highest among the cultivars tested for overall plant quality and black spot resistance. Other roses in the top grouping (Waller-Duncan K-ratio t test) for black spot resistance and overall quality were: Ragtime™ (`Poultieme', a climber from the Courtyard® series), Sophia Renaissance® (`Poulen002', Renaissance® series), Nashville™ (`Poulbico', Town and Country® series), Redwood™ (`Poultry', National Parks® series), Julia Renaissance® (`Poulheart', Renaissance® series), Santa Barbara™ (`Pouloesy', Town and Country® series), and Everglades™ (`Poulege', National Parks® series).

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Understanding physiological drought resistance mechanisms in ornamentals may help growers and landscapers minimize plant water stress after wholesale production. We characterized the drought resistance of four potted, native, ornamental perennials: purple coneflower [Echinacea purpurea (L.) Moench], orange coneflower [Rudbeckia fulgida var. Sullivantii (Beadle & Boynt.) Cronq.], beebalm (Monarda didyma L.), and swamp sunflower (Helianthus angustifolius L.). We measured a) stomatal conductance of leaves of drying plants, b) lethal water potential and relative water content, and c) leaf osmotic adjustment during the lethal drying period. Maintenance of stomatal opening as leaves dry, low lethal water status values, and ability to osmotically adjust indicate relative drought tolerance, with the reverse indicating drought avoidance. Echinacea purpurea had low leaf water potential (ψL) and relative water content (RWC) at stomatal closure and low lethal ψL and RWC, results indicating high dehydration tolerance, relative to the other three species. Rudbeckia fulgida var. Sullivantii had a similar low ψL at stomatal closure and low lethal ψL and displayed relatively large osmotic adjustment. Monarda didyma had the highest ψL and RWC at stomatal closure and an intermediate lethal ψL, yet displayed a relatively large osmotic adjustment. Helianthus angustifolius became desiccated more rapidly than the other species, despite having a high ψL at stomatal closure; it had a high lethal ψL and displayed very little osmotic adjustment, results indicating relatively low dehydration tolerance. Despite differences in stomatal sensitivity, dehydration tolerance, and osmotic adjustment, all four perennials fall predominantly in the drought-avoidance category, relative to the dehydration tolerance previously reported for a wide range of plant species.

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