1. Suppressing Purple Passion (Gynura aurantiaca) Flowering Using Selected Plant Growth Regulators
Jianjun Chen, Russell D. Caldwell and Cynthia A. Robinson
University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL 32703
Gynura aurantiaca is a colorful foliage plant with creeping stems and velvety purple hairs that cover the green leaves. It grows rapidly but is cultivated primarily for those attractive purple leaves. Annually during the spring, this plant produces prominent flowers both in appearance and smell, gaudy and malodorous. Flowering coupled with acquiring an over-grown leggy appearance have been key limitations in its production and use in interiorscaping. This study was undertaken to determine if an available commercial plant growth regulator could inhibit flowering. A-Rest (ancymidol), B-Nine (daminozide), Bonzi (paclobutrazol), cycocel (chlormequat chloride) and florel (ethephon) each diluted to three different concentrations were sprayed in two applications in early spring at two-week intervals. Flowering and bud numbers and plant growth (number of lateral shoots, vine lengths and internode lengths) were recorded. Results indicated that applications of A-Rest, B-Nine, Bonzi and Cycocel, regardless of treatment concentrations, were ineffective in suppressing the flowering of this plant; whereas, florel completely suppressed flowering at the three concentrations used. The florel-treated plants also grew more lateral shoots which produced a compact and dense bush-look, indicating that appropriate concentrations of florel application not only will stop flowering of purple passion but can also improve and prolong its aesthetic value as a potted or hanging-basket interior plant.
2. Differential Responses of Container-grown Ornamental Foliage Plants to Silicon Application
Jianjun Chen1, Russell D. Caldwell1, Cynthia A. Robinson1 and Bob Steinkamp2
1University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL 32703. 2Fafard, Inc. Apopka, FL 32703
Increasing evidence have recently suggested that Si plays important roles in improving plant growth. However, little information is available on Si-effects on container-grown ornamental plants, particularly since most are grown in soilless media where Si sources are greatly limited. The objectives of this research were to evaluate Si absorption and translocation in diverse container-grown ornamental plants and to determine whether Si absorption could improve plant growth. Liners from 39 plant species were potted in peat and pine bark-based soilless media and grown in a shaded greenhouse. Plants were fertigated with a Peter’s 24-8-16 water-soluble fertilizer containing 0, 23.5 and 47 mg·L-1 of Si. Once marketable sizes were reached, plants were harvested and fresh and dry weights determined; Si and other nutrient elements in roots and shoots were measured. Results indicated that 32 of the 39 evaluated species were able to absorb Si with large quantities further transported to shoots. Of the 32 Si-responsive species, 17 showed significant dry weight increases, whereas the other 15 only exhibited Si absorption and translocation with no apparent growth responses. The seven non-responsive plant species showed no significant increases in neither Si absorption and translocation, nor dry weight.
Jianjun Chen, Richard. J. Henny, Lance. S. Osborne, Russell D. Caldwell and Cynthia A. Robinson. University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL 32703
Potted Anthurium is becoming an important indoor flowering foliage plant because of its unique attractive appearance and continuous growth and flowering under interior conditions. However, an interior environment, with controlled optimal temperatures and relative humidity and living plants, is an ideal niche for pest development. Pests such as thrips and two-spotted spider mite on Anthurium have been great challenges to the interiorscape industry because many pesticides have been rigorously restricted for interior-use. Thus, exploiting the genetic potential of cultivar resistance may be the best approach for the control of these pests. In this study, eight of the most popular Anthurium cultivars were evaluated for their resistance to a natural infestation of thrips (Hercinothrips femoralis) and two-spotted spider mite (Tetranychus urticae) under three light levels: 4, 8, and 16 m mol· m-2· s-1?, temperatures of 23.8 to 26.7 oC and a relative humidity of 60%. Results indicated that significant resistant differences exist among cultivars. The cultivars most resistant to thrips were not the most resistant to mite and vice versa. Cultivars that exhibited moderate resistance to thrips were also moderately resistant to mite. Low light intensity appeared to be a factor influencing thrips infestation since control plants that grew under a light intensity of 200 m mol· m-2· s-1 had no observed thrips damage. On the other hand, two-spotted spider mite infestation was not influenced by light intensity.
Jianjun Chen, Yingfeng Huang, Zhen Yang, Russell D. Caldwell and Cynthia A. Robinson
University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL 32703
Containerized ornamental plant production represents extremely intensive agricultural production. An average of 200,000 containers may occupy one acre of surface area to which a large amount of chemical fertilizers will be applied. Because of the use of high-drainage soilless potting mixes coupled with excessive fertigation, a great amount of nutrients, particularly nitrogen and phosphorus are leached, which increases the potential for ground and surface water contamination. Over the past two decades, research has been centered on developing fertigation delivery systems such as nutrient film techniques, ebb-and-flow and capillary mat systems, for reducing leaching. Relatively limited research has been conducted on improving potting medium substrates to minimize nutrient leaching. The objectives of this study were to determine the adsorption isotherm of six different zeolites to ammonium, nitrate and phosphorus, identify and incorporate desired zeolites in a peat/bark-based medium for reducing nutrient leaching in ornamental plant production. Results indicated that the zeolites possess great holding capacities for ammonium, nitrate and phosphorus. Compared to control, ammonium leaching was reduced 70 to 90%, phosphorus 30 to 80% and nitrate 0 to 60% depending on zeolite species and quantity used per pot. Zeolite amended media caused no adverse effects on plant growth. Conversely, biomass increased significantly when compared to that of the control.
5. Evaluation of Interior Performances of Six Cultivars of Aglaonema and Dieffenbachia
Jianjun Chen1, Dennis B. McConnell2, S.V. Pennisi, C. Foster2, Cynthia A. Robinson1 and Russell D. Caldwell1. 1University of Florida, IFAS, Mid- Florida Research and Education Center, Apopka, Florida and 2Department of Environmental Horticulture, Gainesville, Florida
Tissue culture plugs of Aglaonema ‘Cory’, ‘Maria’ and ‘Silver Queen’ and Dieffenbachia ‘Panther’, ‘Snowflake’ and ‘Sport Lynn’ were potted singly in 15-cm pots and grown in a shaded greenhouse under a photosynthetic irradiance (PI) of 100 m mol· m-2· s-1. Eight months after potting, 27 plants of each cultivar were placed in nine interior evaluation rooms under three PI levels (three rooms per level): 4, 8 and 16 m mol· m-2· s-1. In addition, three plants of each cultivar were maintained in the original shaded greenhouse for the duration of the experiment. Number of leaves, plant height and width were monitored monthly. Recently matured leaves were removed at 3-month intervals for 9 months for determination of fresh and dry weight, leaf area, and percentage leaf variegation. Variegated leaf area was assessed using digitized leaf images. Interior PI levels affected growth parameters, but the degree of response was cultivar dependent. Smallest leaves developed on plants grown under 4 m mol· m-2· s-1 and largest leaves developed under 16 m mol· m-2· s-1. Leaf area of D. ‘Sport Lynn’ showed the greatest response and A. ‘Maria’ the least response to PI levels. Percentage leaf variegation of D. ‘Snowflake’ was least affected and D. ‘Sport Lynn’ was most affected by PI levels. Fresh leaf weight of unit area decreased as PI levels decreased from 16 to 4 m mol· m-2· s-1. Based on the results of this study, Aglaonema ‘Maria’ and Dieffenbachia ‘Snowflake’ had the most satisfactory interior performance within their respective genera.
6. Ammonium, nitrate and phosphorus adsorption by zeolites in static and dynamic systems
Y. Huang, J. Chen*, C. A. Robinson and R. D. Caldwell
University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL 32703
Zeolite amendment to soils or soilless media has proven to reduce ammonium leaching, yet little research has been conducted to determine whether zeolites can also retain nitrate and phosphorus. In this study, the adsorption of ammonium, nitrate and phosphorus by six zeolites was quantified using static (shaking study) and dynamic (plant growing in media with fertilizer application) systems. A batch equilibrium shaking test verified that all six zeolites adsorbed ammonium, but three of the six also adsorbed nitrate and the remaining three held phosphorus. When the six zeolites were mixed with plant growing soilless substrates, to which a water-soluble fertilizer was applied weekly, zeolite-incorporated media possessed great holding capacities for ammonium, nitrate and phosphorus.
7. Metal speciation and leachability in compost-formulated substrates
Yang, Z., J. Chen*, C. A. Robinson and R. D. Caldwell
University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL 32703
Biogeochemical speciation and bioavailability of trace metals are a major concern in the assessment of environmental impacts and the use of composts. In this study, metals from three Florida composts: (1) yard trimmings (YT), (2) a mix of YT with biosolid (BS) and (3) a mix of municipal solid waste (MSW) with BS as well as three compost-formulated soilless media were sequentially extracted using H2O, KCl, Na2P2O7, NaOH and HNO3; metal concentrations in corresponding water soluble, exchangeable, complexed, organically bound, solid particulate and residual forms were measured. The three compost-formulated media were also placed in columns and leached with distilled water at a rate of 1.5 mL per minute for five days to determine the leachability of the metals. Metal speciation data indicated that Ba, Cd, Co, Ni and Mo were detectable in trace amounts in all six substrates, and Cu, Cr and Zn were lower than US EPA’s MPL. Across all forms, higher percentages of Cu and Cr were present in either complexed or solid particulate states depending on compost source. However, no matter the compost source, nearly 60% of Zn was in the complexed form, indicating that much of the Zn may be potentially mobile. Metals in water soluble, exchangeable and complexed forms were leachable, suggesting that leaching can reduce metal concentrations if metal content is a concern.
8. Responses of Spathiphyllum Cultivars to Chilling Temperatures
Qu, L., J. Chen*, R. J. Henny, R. D. Caldwell, C. A. Robinson and Y. Huang
University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL 32703
The chilling response of 15 Spathiphyllum cultivars was evaluated using three month-old liners subjected to chilling temperatures of 3.3, 7.2, 10 and 11.1 oC for 2, 5 and 10 days. Significant differences to chilling were found among the cultivars. At the temperatures of 3.3 and 7.2 oC, chilling injury varied from leaf necrosis to the complete death of plants. Younger leaves were more resistant than older ones with the exception of one cultivar. At 10 and 11.1 oC, no visible tissue breakdown occurred. However, plant growth became slower and quality readings were lower than control plants, indicating cultivars that appeared undamaged were actually injured at these temperatures. Such invisible injury could be diagnosed incorrectly as insufficient fertilization or other improper cultural practices because Spathiphyllum is generally considered to be chilling resistance. These findings suggest that genetic differences in chilling resistance exist among Spathiphyllum cultivars and can be used as a basis of cultivar selection.
9. Adventitious Shoot Regeneration of Pothos (Epipremnum aureum) Using leaf explants
Qu, L., J. Chen*, R. J. Henny, Y. Huang, R. D. Caldwell and C. A. Robinson.
University of Florida, IFAS, Mid-Florida Research and Education Center. 2725 Binion Road, Apopka, FL 32703
Pothos is one of the most widely cultivated foliage plants in the ornamental plant industry. However, useful in vitro culture techniques for micropropagation and regeneration have not been established for this species. In this study, in vitro adventitious shoot regeneration was achieved in Pothos using leaf and leaf petiole explants from two cultivars: Jade and Golden Pothos. Explants were prepared from young leaves collected from three-year-old greenhouse grown plants. Regeneration was conducted using MS medium supplemented with growth regulators of NAA, TDZ, zeatine or 2iP in 18 combinations. In the cultivar Jade, callus developed after four weeks and regeneration from the callus occurred in two more weeks on some media containing TDZ and NAA or zeatin and NAA. Similar results occurred with the cultivar Golden Pothos on medium containing zeatin, TDZ and NAA or 2iP and NAA. Callus and regeneration mainly occurred from the cut surface of midrib or surface area close to the midrib. The regeneration rate from leaf explants and leaf petioles was 10% and 30% respectively.
10. Interpretation of Soluble Salts and pH of Bulk Solutions Extracted by Different Methods
Huang, Y., J. Chen*, L. Qu, R. D. Caldwell, C. A. Robinson
University of Florida, IFAS, Mid-Florida Research and Education Center. 2725 Binion Road, Apopka, FL 32703
Soluble salts (SS) and pH are two easily measured parameters and yet critically important to the growth of containerized plants. Because different methods are being used for extracting bulk solutions from potting media, SS and pH readings for an identical medium may differ significantly. Until now a relationship had not been established that would allow the correlation of the metered results obtained from one extraction method to another extraction method. In this study, three commercial media were used to fill 6" pots and were fertilized with either a water-soluble fertilizer or a controlled-release fertilizer. Bulk solutions of the media were extracted three times using four commonly used methods: (1) pour through, (2) saturated extraction, (3) 1:2 (medium: water by volume) and (4) 1:5 dilution. One extraction was made with media only and two additional extractions were conducted at a weekly interval after Pothos (Epipremnum aureum ‘Golden Pothos’) were transplanted into the media. SS and pH of the bulk solutions were measured; the correlation and conversion factors of SS or pH among the four extraction methods were established.
11. Cultivar Differences of Acclimated Ornamental Foliage Plants for Interior Use
*Jianjun Chen1, 2, Richard J. Henny1, 2, Dennis B. McConnell2 and Terril A. Nell2
University of Florida, IFAS, 1Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL 32703. 2Department of Environmental Horticulture, Gainesville, FL 32611
Ornamental foliage plants perform better under interior environments if they are acclimatized during production. Acclimatization is a seriate procedure in which light intensity, nutrient supply and irrigation frequency may be reduced to allow plants to become conditioned before being placed in interior environments. Acclimatization has become a standard practice in the production of foliage plants; however, studies to determine differences in cultivar response to acclimatization procedures are very limited and few if any growers use these differences for the production of better interior foliage plants. In this research, diverse cultivars of Anthurium, Aglaonema, Dieffenbachia and Ficus were subjected to different acclimatization procedures. Light acclimatization was found to play a major role in conditioning plants for interior use. There is pronounced genetic variation among cultivars in response to acclimatization; thus interior performances vary greatly. Cultivars of interior plants are often selected for aesthetic foliage and/or floral characteristics. Our results suggest that the exploitation of the genetic potential of foliage plant cultivars in response to acclimatization may help identify cultivars with the best interactive phenotypes for interior plantscaping.
12. Assessing the Quality of Composted Waste Using Rapid Growing Brassica and Pea Plants
Jianjun Chen, C. A. Robinson and R. D. Caldwell.
University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL 32703.
Using composted wastes as soil amendments is still hampered by uncertainties of the physical, chemical and biological properties of composts. This study was to identify suitable plants for a quick assessment of compost quality using seed germination and plant growth tests. Seeds of Arabidopsis, rapid growing Brassica napus, China doll, corn, eustoma, pea, tobacco, tomato, and wheat were germinated in 13 media using municipal solid wastes, yard trimmings, yard trimmings with biosolids, combined with pine bark and Canadian peat at different ratios. Results indicated that pea and rapid growing Brassica napus were the most suitable plants for assessing the quality of composted-wastes, both having 2-4 day germination time, a varying survival percentage associated with medium quality and also short life cycles. Arabidopsis and tobacco were the best for seed germination index assay in petri plates. China doll and eustoma showed medium specific tendencies but germinated slowly. Corn, tomato and wheat exhibited little salt sensitivity.
13. Multi-metal Contaminated Soils May Be Phytoextractable by Selected Metal Accumulating Mutants
Jianjun Chen1 and Scott D. Cunningham2 .
1University of Florida, IFAS, Mid-Florida Research and Education Center, , 2725 Binion Road, Apopka, FL 32703. 2DuPont Biological and Chemical Sciences, GBC 300, Newark, DE 19714
Metal phytoextraction results in plants taking up great amounts of polluting metals from soils and transporting the metals from roots to harvestable shoots. Unfortunately, limited naturally occurring metal hyperaccumulating plants are known and few of these are able to accumulate multiple metals. This study was to determine whether multiple metal accumulators existed in identified metal mutants. Three Arabidopsis mutants (APb2, APb7 and APb8) and two pea Pisum sativum mutants (brz and dgl) with respective wild types were evaluated after growing in a metal-contaminated soil and a hydroponic culture. Al, Cu, Fe, Mn, Ni, Pb and Zn concentrations in shoots of the Arabidopsis mutants were 2 to 8 times higher than those of the wild type. Pea mutants, brz and dgl, are Fe hyperaccumulators, Fe in shoots of the pea mutants were over 30 times higher and Al, Cu, Mg, Mn, Pb and Zn were 2 to 10 times higher than found in the wild type. These results suggest that metal accumulators exist in identified metal mutants. Upon identification, these accumulators may then be used to abate multiple metals from contaminated soils.
14. Beneficial Effects of Silicon on Container-Grown Ornamental Plants
Jianjun Chen1*, Russell D. Caldwell1, Cynthia. A. Robinson1, and Bob Steinkamp2.
1University of Florida, IFAS, Mid-Florida Research and Education Center. 2725 Binion Road, Apopka, FL 32703. 2Fafard, Inc. 3723 Hogshead Road, Apopka, FL 32703
Silicon (Si) as a beneficial element to the growth of monocots particularly rice and sugarcane has been reported. However, limited research has addressed the effects of Si on container-grown ornamentals. Since most ornamental crops are grown in soilless media where Si concentration is at its minimum, this study was undertaken to determine if Si application could be beneficial to ornamental plant growth. Thirty-nine cultivars from 35 genera of ornamental plants were grown in a soilless medium supplemented with K2SiO3; afterwards, plant growth and Si concentration were measured. General results indicated that all of the plants were capable of absorbing Si through their roots with large amounts found to have been translocated to the shoots, indicating that Si may play certain roles in plant metabolism. More specifically, silicon addition: (1) significantly increased the dry weight of 17 cultivars; therefore, Si could be used as a fertilizer additive for improving the growth of Si-response plants, and (2) mitigated manganese (Mn) toxicity in those acid-love crops, which may be particularly important for improving the plant quality.
15. Identification of Aglaonema Cultivars for Resistance to Chilling Temperatures
Jianjun Chen, R. W. Henley, R. J. Henny, C. A. Robinson and R. D. Caldwell.
University of Florida, IFAS, Mid-Florida Research and Education Center. 2725 Binion Road, Apopka, FL 32703.
Aglaonema is among the most popular tropical ornamental foliage plants used indoors because of its bright foliar variegation, low light and humidity tolerance, and few pests. Aglaonema, however, has been labeled as one of the most chilling sensitive foliage plants. The dark, greasy-appearing patches on leaves injured by chilling can result in completely unsalable plants. With recent breeding activity, more and more Aglaonema cultivars have been developed and released. How new cultivars respond to chilling temperatures is, however, mostly unclear. This study was undertaken to evaluate cultivar responses to chilling temperatures in hopes of identifying chilling resistant cultivars. Twenty cultivars were chilled in coolers at 1.7, 4.4, 7.2, 10, or 12.7 oC for 24 hours, and then placed in a shaded glasshouse for chilling sensitivity evaluation. Results indicate that great genetic variation exists among the cultivars, ranging from no injury at 1.7 oC to severe injury at 12.7 oC. A popular cultivar Silver Queen is the most sensitive, while the new cultivar Stars is the most resistant. There was also a chilling response difference based on leaf maturity. Young leaves showed less injury than either mature or old leaves.
16. Evaluation of Potted Anthurium Cultivar Performances under Interior Environments
Jianjun Chen, R. J. Henny, T. Mellich, R. D. Caldwell and C. A. Robinson
University of Florida, IFAS, Mid-Florida Research and Education Center. 2725 Binion Road, Apopka, FL 32703.
Anthurium cultivars are being produced primarily as cut-flower plants. Whether Anthurium can be used as a flowering interiorscape plant is not well documented. Therefore, five finished Anthurium cultivars were evaluated in interior acclimatization rooms under two light intensities provided by cool-white fluorescent lamps for 12 hours daily: 16 m mol· m-2· s-1 (low light) and 48 m mol· m-2· s-1 (high light). The temperature of the rooms was maintained at 24 oC with a relative humidity of 60%. Total number of open flowers and number of senesced flowers were recorded weekly over a five-month period. In addition, plant canopy height and width, and total number of leaves were measured monthly. Number of open flowers per week ranged from 1.4 to 4.7 under low light, and 2.4 to 6.3 under high light. The cultivar Red Hot showed the best performance with a weekly average flower count of 4.7 under low light and 6.3 under high light. All cultivars continued to produce new leaves ranging from one to five per month under low light, and two to five leaves under high light. Leaves were dark green and shiny under interior conditions. Growth index of ‘Red Hot’ increased 31% under low light and 20% under high light. Results from this study demonstrate that Anthurium can continue to grow and produce flowers under interior environmental conditions. Variation among cultivars indicates that genetic potential exists for selecting improved cultivars based on interior performance.
17. Waste Composts as Components of Potting Media for Rooting Foliage Plant Cuttings
Jianjun Chen, C. A. Robinson and R. D. Caldwell
University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL 32703.
Waste composts have been used as components of potting media for growing bedding, flowering, foliage and landscape plants. However, limited information is available on the use of waste composts for the rooting of foliage plants since conventional rooting is still a prevailing method for foliage plant propagation. In this study, (1) municipal solid waste with biosolids, (2) yard trimmings, (3) yard trimming with biosolids, each in percent combinations with pine bark and Canadian peat were used to formulate 12 potting media. These media along with a control, UF-2 (50% Canadian peat and 50% pine bark), were used for rooting of leaf cuttings (African violet and Christmas cactus), shoots (Aphelandra, Croton, Dracaena, Maranta and Schefflera), cane (Dracaena marginata) and vines (English ivy and Pathos). The pH of the media ranged from 4.6 to 7.0 and soluble salts readings increased from 19 to 2252 m mhos· cm-1. All plant materials rooted in the 13 potting media, but the degree of rooting was greatly affected by the potting media. Analyses of the physical and chemical properties of the potting media indicate that the level of soluble salts is a major factor affecting the degree of rooting. Among the 12 potting media, five were most comparable to, and in some plant species superior to the control. This study suggests that selected waste composts can be reliably used for rooting foliage plants.
18. Silicon as a Beneficial Element for Tropical Foliage Plant Growth
Jianjun Chen and Russell D. Caldwell
University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL 32703
Silicon (Si) is the second most abundant element in soils. Si occurs in soil solution mainly as silicic acid in the concentration range of 0.1 to 0.6 mM. The beneficial effect of Si to terrestrial plants has been established in species of Equisetaceae, Cyperaceae, Gramineae, and Urticaceae. However, little information is available on the effects of Si on tropical foliage plants. We evaluated 39 foliage plant cultivars in thirty-five genera for their responses to Si. Factors taken into consideration for this evaluation were leaf area and thickness, chlorophyll content, photosynthesis, transpiration, plant fresh and dry weights, nutrient concentrations in growth media and in plant tissues. It was observed that all the plants were capable of absorbing some amount of Si, and majority of absorbed Si was transported into shoots. The difference in accumulation of Si was found to be 10 fold among the tested plant species. Si fed plants had thicker leaves and stiffer leaf hairs compared to the control. The beneficial effects of Si on these tropical foliage plants include (1) enhancement of plant growth, (2) increase in physical strength, (3) resistance to environmental stresses, (4) mitigation of nutrient imbalance.
19. Increased Accumulation of Lead in the Bronze Mutant (E107) of Pea (Pisum sativum L.)
Jianjun Chen1, J. W. Huang2, and S. D. Cunningham3.
1University of Florida, IFAS, Mid-Florida Research and Education Center. 2725 Binion Road, Apopka, FL 32703. 2Phytotech Inc. Monmouth Junction, NJ 08852. 3DuPont Environmental Biotechnology, Newark, DE 19713
Phytoextraction of Pb from contaminated soils requires plants that are able to accumulate large amount of Pb in shoots. To search for Pb-hyperaccumulating plants, we screened over 250 cultivars or strains from 50 plant species using Pb-contaminated soils. Of the plants evaluated, a pea mutant (E107) accumulated significantly higher concentration of Pb in shoots. This mutant was reported previously as an Fe-hyperaccumulator, which was due in part to an increased activity of iron (III) reductase in the root. When both E107 and its wild type, Sparkle, were grown in a Pb-contaminated soil for 4 weeks, Pb concentration in shoot of E107 was 11 fold higher than that of Sparkle. We also investigated the phenomenon of chelated-enhanced Pb phytoextraction by amending the soil with EDTA. Interestingly, the phenotypic Pb-accumulation difference between E107 and Sparkle disappeared. These results indicated that either the increased activity of iron (III) reductase or a closely related phenomenon in E107 significantly enhances Pb-extraction efficiency. As it is ultimately desirable to eliminate exogenous chelate additions, this phenomenon should be further explored. Possible interpretations will be discussed.
20. A Detached Single Leaf-Assay Method for Testing Aglaonema Responses to Chilling Temperatures
Jianjun Chen, R. W. Henley, R. J. Henny, and R. D. Caldwell
University of Florida, IFAS, Mid-Florida Research and Education Center. 2725 Binion Road, Apopka, FL 32703.
Aglaonema is one of the most popular tropical ornamental foliage plants used indoors. Sensitivity to chilling temperatures is, however, a limitation to its production and successful utilization, especially with some cultivars. With increased release of new cultivars, it would be beneficial if the chilling response of a new cultivar could be known prior to its commercial production. In this study, a detached single-leaf assay was developed to compare with whole-plant evaluation. Results from 10 cultivars chilled at three levels of chilling temperatures (1.7, 7.2, and 12.8 oC) for 24 hours revealed that there was a significant high correlation between the single-leaf assay and whole-plant evaluation. Among the 10 cultivars tested, Silver Queen was the most sensitive, whereas Star and Black Lance were the most tolerant. There also was a chilling response difference based on leaf maturity. The order of chilling sensitivity was matured leaves ³ old leaves > young leaves. Thus, to test chilling responses of a cultivar, a detached single matured leaf was chilled for 24 hours or longer will give information on the degree of sensitivity of the cultivar. This method should be a valuable tool for breeders, growers, and other segments of the foliage plant industry.