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Hector R. Valenzuela and Joseph DeFrank

Living mulches offer a low-input alternative to achieve weed control while minimizing herbicide applications, decreased fertilizer leaching, insect and nematode management. and improved soil texture. A study was conducted to evaluate the effect of a Rhodes Grass (Chloris gayana cv. Katambora) living mulch on the growth and productivity of ten eggplant. Solanum melongena, cultivars grown under fertigation. The living sod was established at the Univ. Hawaii Waimanalo Experiment Station in June 1992. Soil analysis was taken before experiment initiation. Ten eggplant cultivars were transplanted on both living-mulch and control (woven-polyethelene mulch) plots on 4 March 1993. Weekly or bi-weekly harvests were conducted for six months. beginning on 19 May 1993. In addition plant height and canopy dimensions were determined on 16 April. and 10 Nov. Plant growth was monitored throughout the experiment. Soil samples were taken from the eggplant rhizosphere, hare-ground and in Rhodes grass monoculture, for nematode count determinations. Soil samples were also taken for nutrient determination after completion of the experiment. Overall yields were greater in the polyethelene mulch than in the living mulch plots. A differential response was observed on the response of cultivars to cropping system. However the most vigorous cultivars performed well in both systems. The living mulch system showed potential for nematode management in eggplant agroecosystems.

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Amy N. Wright, Robert D. Wright, Jake F. Browder, and Brian E. Jackson

Posttransplant root growth is critical for landscape plant establishment. The Horhizotron provides a way to easily measure root growth in a wide range of rhizosphere conditions. Mountain laurel (Kalmia latifolia L.) plants were removed from their containers and planted in Horhizotrons in a greenhouse in Auburn, Ala., and outdoors in Blacksburg, Va. Each Horhizotron contained four glass quadrants extending away from the root ball, and each quadrant within a Horhizotron was filled with a different substrate (treatment): 1) 100% pine bark (Pinus taeda L., PB), 2) 100% soil, 3) a mixture of 50 PB: 50 soil (by volume), or 4) 100% soil along the bottom of the quadrant to a depth of 10 cm (4 inches) and 100% PB layered 10 cm (4 inches) deep on top of the soil. Root growth along the glass panes of each quadrant was measured biweekly in Auburn and weekly in Blacksburg. Roots were longer in all treatments containing pine bark than in 100% soil. When pine bark was layered on top of soil, roots grew into the pine bark but did not grow into the soil. Results suggest that amending soil backfill with pine bark can increase posttransplant root growth of container-grown mountain laurel.

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David N. Sasseville, Robert J. Kremer, Wm. Alan Bergfield, and Thourava Souissi Lincoln

Benlate 50 DF has been implicated in causing long term damage to leatherleaf ferns. Damage to leatherleaf fern including frond distortion, discoloration and growth suppression continues to occur even after two or more years following last Benlate application. Electron micrographs of affected plants roots indicate a loss of root hairs and a proliferation of associated soil bacteria on the root surface compared to healthy plants. Plants with history of continued Benlate application have extensive bacterial colonies embedded on the root surface, but these colonies were not parasitic. Lcatherleaf fern plants which only had their rhizomes dipped in Benlate at planting lacked the embedded colonies, but were extensively covered with bacteria. Bioassays of bacteria taken from the rhizoplane and rhizosphere of the these leatherleaf ferns showed that these bacteria have the ability to produce growth regulators and/or toxins which may be detrimental to plant growth when absorbed through the root. Consequently, Benlate may be influencing fern growth indirectly by modifying bacteria composition of the growing media to favor proliferation of deleterious, non-parasitic bacteria.

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C. Stevens, V. A. Khan, M.A. Wilson, D. J. Collins, J. E. Brown, and J. Y. Lu

Agriplastic black mulch (BM), row cover (spunbonded) plus black mulch (RBM) and solarized soil treatments plus black mulch (SBM). row cover plus black mulch on solarized soil (RSBM) and row cover plus solar&d soil (RSBS) increased Floradade tomato yield from 56 to 285%. number of tomatoes and plant height compared to the non-solarized bare soil (BS). When comparing increased growth response (IGR) of the plants grown in the solarized soil with no row cover agriplastic treatments, there was no significant differences among them. When comparing the IGR parameters of tomato plants grown under SBS, BM, and RBS there were no significant differences among them. Spunbonded row cover treatments increased IGR of tomatoes over all treatments without row cover. A significant increase in plant growth promoting rhizobacteria (PGPR) was observed in the rhizosphere soil of Floradade tomatoes grown in solarized soil alone and in those other agriplastic treatments compared to bare soil. There appear to be no differences in PGPR population among SBS and all agriplastic treatments.

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Dariusz Swietlik

The purpose of this study was to determine the effect of Ca: NH4 ratio in the rhizosphere of hydroponically grown sour orange seedlings (SO) (Citrus aurantium L.) on the plants' vegetative growth and N uptake. The experiment was prompted by our observation that application of N in the form of NH4 in conjunction with CaCl2 was more efficient in eliminating N deficiency in field-grown grapefruit trees than the same rates of N applied in the form of NH4NO3 without CaCl2. About 40-cm-tall SO were pruned back to the 4th leaf and grown for 6 weeks in nutrient solutions containing 5 mm NH4 + at CaCl2: NH4 + molar ratios of 1.0, 1.3, 1.6, 1.9, 2.2, or 2.5. In an additional treatment, NO3 was used as the sole source of N at CaCl2: NO3 ratio of 1:1. The level of Ca:NH4 ratio had no effect on new leaves number, shoot growth, total and average leaf area, specific leaf weight, as well as leaf, stem, and tap root dry weight. However, lateral root dry weigh decreased at Ca: NH4 ratio of 2.5. No growth differences were found when the plants were supplied with NH4 + vs. NO3 at Ca:N molar ratio of 1:1.

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G.K. Panicker, G.A. Weesies, A.H. Al-Humadi, C. Sims, L.C. Huam, J. Harness, J. Bunch, and T.E. Collins

Even though research and education systems have transformed agriculture from a traditional to a high-technology sector, soil erosion still remains as a major universal problem to agricultural productivity. The Universal Soil Loss Equation (USLE) and its replacement, the Revised Universal Soil Loss Equation (RUSLE) are the most widely used of all soil erosion prediction models. Of the five factors in RUSLE, the cover and management (C) factor is the most important one from the standpoint of conservation planning because land use changes meant to reduce erosion are represented here. Even though the RUSLE is based on the USLE, this modern erosion prediction model is highly improved and updated. Alcorn State Univ. entered into a cooperative agreement with the NRCS of the USDA in 1988 to conduct C-factor research on vegetable and fruit crops. The main objective of this research is to collect plant growth and residue data that are used to populated databases needed to develop C-factors in RUSLE, and used in databases for other erosion prediction and natural resource models. The enormous data collected on leaf area index (LAI), canopy cover, lower and upper biomass, rate of residue decomposition, C:N ratio of samples of residues and destructive harvest and other gorwth parameters of canopy and rhizosphere made the project the largest data bank on horticultural crops. The philosophy and methodology of data collection will be presented.

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M.L. Matheny

One of the main difficulties in controlling root diseases biologically has been the inability of biocontrol agents to establish and persist in the rhizosphere. The inability of biocontrol agents to establish and persist is often attributed to competition from indigenous microorganisms for space and nutrients and to fluctuations in environmental conditions. The use of biocontrol agents over the entire geographic range of a crop also has been limited by differences in environmental and edaphic conditions from field to field and region to region. An advantage of hydroponic crop production in greenhouses is that environmental conditions such as temperature, moisture, pH, and growth medium can be consistently controlled in a house and from site to site. An additional advantage of many hydroponic systems is that they are virtually sterile upon planting. This initial period of virtual sterility greatly reduces competition for an introduced biocontrol agent. In addition, these systems are usually pathogen-free upon planting allowing the establishment of a biocontrol agent prior to pathogen introduction. Last, the temperatures, high moisture levels, and pH ranges of hydroponic systems can be ideal for the proliferation of many biocontrol agents. With all of these advantages for the use of biocontrol agents in hydroponic systems, our company, and many labs around the world, have focused their attention on developing biological control agents for these systems. I will provide a review of research focused on controlling root diseases of vegetables grown in rockwool and other hydroponic systems.

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Thierry Vrain, Robyn DeYoung, John Hall, and Stan Freyman

Cover crops used in red raspberry plantings (Rubus idaeus L.) are often good hosts of the root-lesion nematode (Pratylenchus penetrans Filipjev & Sch. Stekoven), a major soilborne pathogen of raspberry. The effects of two susceptible cover crops, white clover (Trifolium repens L.) and barley (Hordeum vulgare L.), planted in between rows, on nematode density and growth of raspberry plants were compared to those of three cover crops resistant to the nematode: redtop (Agrostis alba L.), creeping red fescue (Festuca rubra L.), and `Saia' oat (Avena sativa L.). Nematode multiplication in raspberry roots and in cover crop roots was assessed over 4 years. Growth and vigor of plants were estimated at the end of the experiment by counting primocanes and determining height and biomass. Nematode multiplication was suppressed in roots of `Saia' oat, fescue, and redtop compared to barley or white clover. Nematode density in roots and rhizosphere soil of raspberry was not affected by the choice of cover crops. Nematode suppression in the three resistant cover crops did not translate into increased vigor of raspberry plants.

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J.O Becker and U.K. Schuch

A rapid screening system was developed to identify plant-beneficial rhizobacteria useful in protecting nursery seedlings against damping-off caused by Rhizoctonia solani. Ornamental and agricultural crops were planted into 100 soil samples that were collected from various fields throughout California. More than 7000 bacterial strains from the rhizosphere of these crops were isolated and tested in vitro for antibiosis against R. solani AG4. In a second tier, 600 active strains were tested in planting trays seeded with radish (Raphanus sativus `Cherry Belle'). Each planting cell filled with commercial potting mix contained millet-grown R. solani inoculum in the center and eight radish seeds at the periphery. Bacteria were cultured for 24 hr at 25°C in 10% tryptic soy broth and were applied as a drench at 1 × 107 cfu/cc to each cell. Trays were incubated in a growth chamber at 21°C and a 10-hr photoperiod. Post-emergence damping-off occurred within 8 to 9 days after planting, and no further losses were observed after 14 days. Approximately 0.5% of the original 7000 bacterial strains tested reduced damping-off significantly. Fifteen bacterial strains controlled Rhizoctonia damping-off by 30% to 60% compared to the non-treated control.

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W.A. Bergfield, D.N. Sasseville, R.J. Kremer, and T. Souissi

Pesticides are used extensively in ornamental production. Studies of repeated pesticide applications indicate that microbial changes occur in the rhizosphere of the plant. In addition to controlling the target pest, often a population shift of bacteria may occur. This has been previously shown in research associated with leatherleaf fern [Rumohra adiantiformis (Forst.) Ching] and the fungicide benomyl. Rhizobacteria (root-associated bacteria) of anthurium (Anthurium andraeanum) were investigated with respect to total populations and isolates that are potentially phytotoxic. The anthurium sample roots were taken from commercial Jamaican production sites. The sites had either a benomyl or non-benomyl history. Rhizobacterial populations were estimated by dilution plating and subcultures were taken for a phytotoxicity bioassay. Micrographs of samples were prepared to examine treatment effects on the morphology of roots. Rhizobacteria populations were frequently at 106 colony forming units per gram fresh weight. Consistently, greater than 50% of the isolates from each treatment were potentially phytotoxic. However, in the benomyl history samples, there was a greater diversity of phytotoxic isolates.