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  • Author or Editor: Byoung Ryong Jeong x
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Ageratum and salvia were grown in hydroponic solutions containing either NH4 +, NO3 -, or both NH4 + and NO3 - with or without Cl- to study changes in solution pH and ion uptake rate. pH of both NH4 + and NH4 + + NO3 - solutions was steadily decreased as time passed. A drop in pH front 6.50 to 3.57 within 3 days was recorded with NH4 +. The pH changes were also affected by the presence of Cl-. The NO3 - treatment maintained its initial solution pH over time regardless of the presence of Cl-. pH change by ageratum was greater than that by salvia, especially when plants were in NH4 + + NO3 - solution. N uptake was maximum in NH4 + + NO3 - solution with Cl-. Uptake of NO3 - was suppressed by NH4 +, but NH4 + uptake was not affected by NO3 -. NH4 + and NO3 - counteracted each other in influencing the Cl- uptake. Uptake of other ion was also affected by plant species as well as N source and Cl-. In ageratum transpiration rate was lowered by Cl- in both NH4 + and NO3 - treatments.

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This study was carried out to determine the interaction among NH4 +, NO3 -, and Cl- ion uptake and to find the causes of NH4 + -related toxicity symptoms in plants fed with NH4 + as a sole nitrogen source. Seedling plants established in peat-lite and rockwool media were fed with nutrient solutions containing either NH4 + or NO3 - or both NH4 + plus NO3 - with or without Cl-. Plants grown with NH4 + + Cl- contained the highest levels of Cl-. Plants fed with NO3 - + Cl- also showed high levels of Cl- in the tissue. The growth and tissue Cl- contents of plants fed with NH4 + were not affected by changes in Cl- concentration in the nutrient solution. Plants fed with NH4 + that was ion-balanced by high levels of SO4 2- plus low or no Cl- still developed the NH4 + -related toxicity symptoms. This indicates that NH4 + -related toxicity symptoms occur independently of Cl-. It was also shown that the activity of Cl-, a counterion for NH4 + uptake, was suppressed by NO3 -.

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A top-and-bottom split root system of Lycopersicon lycopersicum `Burpee's Pixie' was developed using a nonferromagnetic phenolic foam growing medium. The objective of the study was to observe hydrodynamic activity in the roots and substrate when one side of the split root system was dehydrated. After withholding water for 22 days from the top block, the plant and substrate were scanned for 46.5 hours every 30 min using a Siemens 1.5 tesla magnetron whole body imaging system operating at 63 MHz. Resulting images were compiled into a time lapse movie and clearly showed selective root hydration and dehydration on the dry side of the split root system. Those changes in the root MRI signal intensity suggest a cyclic hydration of the roots and a partitioning of water among roots in dry environment.

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Ageratum houstanianum Mill. (tolerant), Tagetes patula L. (French marigold, very sensitive), Petunia hybrida Vilm. (sensitive), and Salvia splendens F. Sellow et. Roem & Schult. (very sensitive) were grown with NO3 -, NH4 +NO3 -, or NH4 + as the N source to examine whether NH4 +-related growth suppression (NH4 +-RGS) in the NH, -sensitive species was associated with excessive Cl- absorption from the nutrient solution. Amounts of Cl- applied were 4 or 11 meq·liter-1 (Expt. 1) and 0 or 4 meq·liter-1 (Expt. 2). When fertilized with NH4 + as a sole N source, marigold, petunia, and salvia showed NH4 +-RGS symptoms with yield reduction regardless of altered Cl- levels in the nutrient solution, while ageratum showed no such symptoms. When grown with NH4 + solution, these sensitive plants had shoot fresh and dry weight reductions of ≈ 50% compared to those grown with the NH4 + + NO3 - solution. Plants fertilized with NH4 + showed more severe NH4 +-RGS symptoms when grown in rockwool (RW) than in peat-lite mix (PL). The NH4 +-grown plants contained more NH4 + and much more Cl- in the tissue than plants fertilized with NO3 - or NH4 + + NO3 -, irrespective of the Cl- level in the nutrient solution. However; NH4 +-RGS symptoms in marigold, petunia, and salvia appear to be caused by the uptake of NH4 +, but not in association with Cl- from the nutrient solution.

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Trichoderm a spp. are currently being investigated for biological control of soil-borne pathogens and their potential to enhance plant growth and development. The influence of T. harzianum and T. hamatum on growth of 7 bedding plant species was Investigated. Trichoderm a formulated in peat moss and wheat bran, was mixed into germination and growing media at 1 × 106 cfu per gram of medium. Seeds were germinated in plugs and later grown in cellpacks containing a treated and non-treated medium until market stage. Plants were evaluated by measuring height, fresh and dry weight, and number and timing of flowering. Growth enhancement was found in marigold (14.8% dw), petunia (15.5% dw) and tomato (38.2% dw), however, no significant differences were seen in celosia, impatiens, salvi a and vinca. Results suggest that growth enhancement by Trichoderm a is species dependent and that Trichoderm a applied in the plug mix remains-effective through marketing stage.

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Toxicity symptom of micronutrients copper, magnesium and zinc were investigated for geranium, marigold, vinca and zinnia. Plants were grown in peat-lite mix in 11 cm plastic pots and watered with nutrient solutions containing 0.05, 0.5, 1, 5, 10 mM concentrations of Cu2+, Mg2+ and Zn2+. In most species, the concentrations of these micronutrients higher than 5 mM greatly reduced plant growth and induced stem and foliar toxicity symptoms. Toxic levels of Cu2+ and Zn2+ reduced plant and leaf sizes without producing leaf spots in all species tested. Toxicity symptom of Mn2+ were characterized by numerous chlorotic or brown leaf spots. Visual leaf toxicity symptoms of these 3 micronutrients in each species are illustrated.

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Effect of combination and concentration of growth regulators on the regeneration of pepper plant from different explant tissues was studied. Seedlings were grown aseptically in 400 ml glass bottles containing MS agar medium at 26±2C under a 16 h·d-1 photoperiod (2000 lux, florescent lamps). Explants taken from 4 week-old seedlings were cultured under these conditions on 40 ml of MS agar (8 g·liter-1) medium containing 3 g·liter-1 sucrose in a 400 ml glass bottle. Primary and subsequent leaves attached to petiole regenerated better than cotyledon and hypocotyl. Among the combinations of different concentrations of cytokinin and auxin added in the medium, a combination of 5 μM IAA with either 10 μM zeatin or 10 μM BA gave the best regeneration. With these combinations, regeneration frequency of multiple shoots from the primary and subsequent leaves was greater than 70%. Regenerated shoots rooted readily in MS agar medium containing 3 g·liter-1 sucrose and 0.5 μM NAA.

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A non-destructive in vivo spectroscopic method for leaf chlorophyll (Chl) measurement was developed. Spectroscopic analyses of intact leaves of ageratum, petunia and salvia showed strong correlations between leaf light absorption at 723 nm and Chl-a contents. NH4 + increased Chl contents in both ageratum and petunia whereas NO3 - increased Chl contents in salvia. Plants fed with NH4 + + NO3 - also contained higher Chl. Chl-a/-b ratio in salvia was lowered by NO3 -. Ageratum, petunia and salvia grown with either NH4 +, NO3 -, or NH4 + + NO3 - were also examined for their light absorption characteristics. Light absorption at 705 nm by ageratum and petunia leaves was increased by NH4 + treatment. NH4 + is believed to have changed the structure of photosystem I in both ageratum and petunia but not in salvia. This result explain reasons for salvia's sensitivity to NH4 + fed as a sole N source.

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A non-destructive in vivo spectroscopic method for leaf chlorophyll (Chl) measurement was developed. Spectroscopic analyses of intact leaves of ageratum, petunia and salvia showed strong correlations between leaf light absorption at 723 nm and Chl-a contents. NH4 + increased Chl contents in both ageratum and petunia whereas NO3 - increased Chl contents in salvia. Plants fed with NH4 + + NO3 - also contained higher Chl. Chl-a/-b ratio in salvia was lowered by NO3 -. Ageratum, petunia and salvia grown with either NH4 +, NO3 -, or NH4 + + NO3 - were also examined for their light absorption characteristics. Light absorption at 705 nm by ageratum and petunia leaves was increased by NH4 + treatment. NH4 + is believed to have changed the structure of photosystem I in both ageratum and petunia but not in salvia. This result explain reasons for salvia's sensitivity to NH4 + fed as a sole N source.

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