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Joseph P. Albano and William B. Miller

Excised roots of `First Lady' marigold (Tagetes erecta L.) grown in an aerated 0 Fe nutrient solution had Fe(III)-DTPA reductase activity 14-fold greater, and an enhanced ability to acidify the rhizosphere than plants grown in a solution containing 0.018 mm (1 ppm) Fe-DTPA. Reductase activity and rhizosphere acidification of plants grown in 0.018 and 0.09 mm Fe-DTPA were similar. Manganese concentration in leaves of plants grown in the 0 Fe treatment was 2-fold greater than in leaves of plants grown in the 0.018 mm Fe-DTPA treatment. These results indicated that `First Lady' marigold is an Fe-efficient plant that possesses both an inducible or adaptive reductase system and the ability to acidify the rhizosphere, and that these Fe-efficiency reactions do not occur when Fe is sufficient. Chemical name used: ferric diethylenetriaminepentaacetic acid, monosodium salt (Fe-DTPA).

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John Jifon*

Use of plastic mulch to increase rhizosphere temperatures is a common practice in spring production of vegetable crops. However, supraoptimal soil temperatures during the fruit maturation period in early summer can impair root function and reduce produce quality. The effects of colored plastic mulch on rhizosphere temperature and `Primo' muskmelon root respiration were investigated in the field during Fall (Aug.-Nov. 2002) and Spring (Mar.-May 2003) seasons. Rhizosphere temperatures (measured at 0.1 m below the soil surface with thermo-couples) and respiration under four plastic mulches (black, silver, white, and clear), and a bare ground control were studied. The soil warming properties of the different mulches differed between Spring and Fall. Bare ground rhizosphere temperatures declined from ≈33 to 21°C in the Fall and increased from 14 to 26 °C in Spring. In both studies, black and clear plastic mulches had the highest rhizosphere warming effects (3-8 °C) compared to bare ground. In the Fall, average midday soil temperatures under the white and silver mulches were 2-3 °C cooler than the bare ground treatment. Canopy establishment was accelerated by plastic mulches in Spring but not in Fall. Root + soil respiration was positively correlated with measured rhizosphere temperatures (r = 0.69), with the highest respiration rates recorded under the clear and black plastic mulches. More than 80% of fruits from the clear plastic treatment were deformed and unmarketable. The number of marketable fruit was similar among the black, white and silver mulch treatments and significantly greater (32% in Spring & 12% in Fall) than in the bare ground treatments.

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Jingjing Yin, Nina L. Bassuk, Madeline W. Olberg, and Taryn L. Bauerle

specific range of rhizosphere conditions that are most suitable for root regeneration ( Richardson-Calfee and Harris, 2005 ), which could also lead to the difference in optimal transplant timing between Q. bicolor and Q. macrocarpa although both of them

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Rebecca L. Darnell, Bruno Casamali, and Jeffrey G. Williamson

.5–6.0 ( Bagnaresi and Pupillo, 1995 ; Cohen et al., 1997 ). Thus, the pH of the rhizosphere can have a profound effect on FCR activity and subsequent ferrous iron uptake. Although soil pH effects on nutrient availability and uptake are known, it is unclear if the

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Julie Guckenberger Price, Amy N. Wright, Kenneth M. Tilt, and Robert L. Boyd

time in a variety of rhizosphere conditions. The Horhizotrons were placed on greenhouse benches at the Paterson Horticulture Greenhouse Complex, Auburn University, Auburn, AL (day/night temperatures set at 26/21 °C). Initial growth indices of plant

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Alejandro Alarcon, Frederick T. Davies Jr., Robin L. Autenrieth, David Wm. Reed, and David A. Zuberer

A phytoremediation study in a 3 × 3 × 2 factorial experimental design was conducted to determine the effect of Glomus intraradices (AMF) inoculation and inorganic fertilization on the growth and development of Lolium multiflorum cv. Passarel Plus, and on the degradation of total petroleum hydrocarbons (TPH). The 80-day study was done with pots containing sandy soil. Seedlings of L. multiflorum were transplanted to uncontaminated or soil contaminated with Arabian crude oil (ACO) at concentrations of 3000 and 15,000 mg·kg-1. Half of the seedlings were inoculated with 500 spores of AMF. Plants were fertilized with Long Ashton Nutrient Solution (LANS) at 0.5×, 1.0×, or 2.0× strength, modified to supply 30 μg·mL-1 P to maximize the AMF establishment. Total plant dry weight and leaf antioxidant activity were reduced by ACO when compared to control plants. The LANS fertilization enhanced plant growth under ACO-contamination, and allowed similar antioxidant activity in plants exposed to 15,000 mg·kg-1. Soil rhizosphere respiration was increased by LANS, particularly with 15,000 mg·kg-1 ACO. AMF inoculation did not enhance plant growth, antioxidant activity, or microbial respiration. The average root colonization was around 30% in contaminated and uncontaminated rhizospheres, indicating that the tolerance of AMF symbiosis to ACO. Greater TPH degradation was achieved in non-AMF plants at 3000 mg·kg-1 ACO in combination with 0.5× LANS. LANS-fertilization with 1.0× or 2.0× did not enhance TPH-degradation when compared to 0.5× LANS.

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C.F. Scagel

We assessed whether addition of arbuscular mycorrhizal fungus (AMF) inoculum or rhizosphere organisms from AMF inoculum alters aspects of flowering, corm production, or corm quality of harlequin flower (Sparaxis tricolor) for two growth cycles after inoculation. Using pasteurized and nonpasteurized growth medium, plants were inoculated with either inoculum of the AMF, Glomus intraradices, or washings of the inoculum containing rhizobacteria. Shoots of plants inoculated with AMF emerged 2 days earlier than shoots on noninoculated plants or plants inoculated with inoculum washings. Flowers on AMF-inoculated plants opened 7-8 days earlier and plants produced more flowers per plant and per inflorescence than noninoculated plants. AMF-inoculated plants partitioned a higher proportion of biomass to cormel production than to daughter corms and had higher concentration and contents of zinc, sulfur, nitrogen, amino acids, and carbohydrates than corms from noninoculated plants. The rhizosphere organisms associated with the AMF inoculum influenced several measures of plant development, growth, and corm production suggesting that there are organisms associated with our AMF inoculum that have beneficial effects on the growth and productivity of harlequin flower. While inoculation with AMF can promote shoot emergence, leaf production, and flower production of harlequin flower, inoculation also alters aspects of biomass partitioning and corm composition that play an important role in the production of this crop for corms and cormels.

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Irene Nyambura Mbugua

Field experiments were performed to verify the influence of polyethylene mulches (red, blue, gray, black, and yellow) on the development and yield of two varieties of cucumber (Cucumis sativus), a hybrid, `Turbo' and an open-pollinated, `Marketmore 76'. The influence of the mulches on the population dynamics of the adult striped cucumber beetle (Acalymma vittatum) was also observed. Rhizosphere temperature, reflected surface temperatures, reflected wavelength, vine length, leaf number, leaf area, total fruit produced, and number of marketable fruit were some of the characteristics measured. A split plot experiment in a randomized blocks design with three replications was used. In relation to plant growth and yield, plants grown on red mulch showed the best growth and yield overall compared to blue, gray, black, and yellow colored mulches, The incidence of the cucumber beetles was highest in the yellow colored mulch. The `Turbo' variety had the highest fruit number in almost all of the colors of mulch compared to the open pollinated `Marketmore'. It is suggested that the differential growth and development of cucumbers was influenced by the rhizosphere temperature as well as the light spectrum reflected from the plastic. The response of the beetles to the mulch was mainly attributed to the different wavelengths reflected from the various mulches.

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Tracy L. Wacker, Gene R. Safir, and Christine T. Stephens

Asparagus (Asparagus officinalis L.) seedlings inoculated with the sicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum (Thaxt. sensu Gerd.) Gerd. & Trappe (GF) d Fusarium oxysporum (Schlect.) Snyd. & Hans. (FO) were grown under field and greenhouse conditions. In the fi, shoot volumes of GF-inoculated plants were greater than nonGF plants from the 3rd through the 13th month of growth. By the 14th month, GF-inoculated plants grown in high-P soils had significantly lower disease ratings than nonGF plants grown in low-P soils, and rhizosphere populations of FO were lowest in high-P soils, regardless of VAM status. In greenhouse studies, FO inoculation of VAM-infected asparagus plants reduced GF root colonization levels under well-watered (0 MPa), but not under water stress, conditions (- 1.5 MPa). Well-watered plants inoculated with both FO and GF were less diseased and sustained lower rhizosphere populations of FO than plants inoculated with FO alone. The differences in FO populations and disease ratings in these studies were apparently unrelated to final plant tissue P levels.

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M. Tagliavini, A.D. Rombolà, and B. Marangoni

Pear rootstocks differ in tolerance to calcareous and alkaline soils. Roots of Fe-efficient dicots react to Fe-deficiency stress by strongly enhancing the Fe3+-reductase system, termed turbo-reductase, and by lowering the rhizosphere pH. In this study, we tested whether such adaptation mechanisms characterize pear and quince genotypes. Two trials were performed using micropropagated plants of three quince rootstocks (BA29, CTS212, and MC), three Pyrus communis rootstocks (OH × F51 and two selections obtained at Bologna Univ.: A28 and B21) and of two pear cultivars (Abbé Fétel and Bartlett, own-rooted). In the first trial, plants were grown in a nutrient solution with [Fe(+)] and without iron [Fe(–)] for 50 days. Their root iron-reducing capacity (IRC) was determined colorimetrically, using ferrozine and Fe-EDTA, and Fe uptake of Fe(+) plants was estimated. In the second trial, the rhizosphere pH of plants grown in an alkaline soil (pH in water = 8.3) was measured by a microelectrode. With the only exception of pears OH × F51 and A28, whose IRC was similar in Fe(+) and Fe(–) plants, the Fe-deficiency stress caused a significant decrease of the IRC. Among the Fe(–) plants, the two pear OH × F51 and A28 had higher IRC than the quince rootstocks and the cultivar Abbé F. When plants were pretreated with Fe, IRC was highest in the P. communis rootstocks (more than 50 nmol Fe2+/g fresh weight per h), intermediate in the own-rooted cultivars, and lowest in the quinces (<15 nmol Fe2+/g fresh weight per h). Fe uptake proved to be linearly and positively correlated with root Fe-reducing capacity (r = 0.91***). Rhizosphere pH, averaged over the first 2 cm from root tips, was highest in quince MC (7.2), intermediate in the other two quinces and in the cultivar Abbé F. (6.2–6.6) and lowest in the pear rootstocks and in the cultivar Bartlett (5.2–5.5). The results indicate that roots of pear and quinces do not increase their ability to reduce the iron under Fe-deficiency stress. The genotypical differential tolerance to iron chlorosis likely reflects differences in the standard reductase system and in the capacity of lowering the pH at soil/root interface. The determination of the root IRC appears very promising as a screening technique for selecting efficient Fe-uptake rootstocks.