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  • Author or Editor: P.D. Roberts x
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Recirculating irrigation systems (RISs) conserve water and decrease fertilizer application, providing cost-effective alternatives to other watering methods in greenhouses. However, RISs can potentially become contaminated from spray or drench pesticide applications. In this study, we determined the amount of metalaxyl residues (the active ingredient in Subdue) in RISs over 3 and 6 weeks using HPLC analysis. Also examined was the potential use of constructed wetlands for the remediation of RIS water contaminated with metalaxyl. Metalaxyl was found to persist in a RIS over 6 weeks with no decrease in concentration. After repeated metalaxyl treatments over an 11 month period, a possible breakdown product or chemical modification of metalaxyl was present in the RISs. Drench applications, 150 ml of an 18.8 ppm metalaxyl solution, (recommended dosage) resulted in 0.5 to 3.0 ppm contamination levels in the RISs. Small scale (≈70 L void volume), indoor, constructed wetlands (two planted with Scirpus and Iris, two unvegetated) were treated with 420 mg metalaxyl. Limited breakdown of metalaxyl occurred in the constructed wetlands during the first 30 days after treatment. After 3 months, metalaxyl concentrations in all wetlands had decreased or were below detection levels. This indicates a possible selection of microbial populations capable of metabolizing or degrading metalaxyl.

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Leaf water relations and gravimetric water loss as influenced by K rate (25, 75, 150, 300, 450 and 600 ppm) and moisture stress conditioning (MSC - exposing plants to 4 sub-lethal dry down cycles) were determined for salvia (Salvia splendens `Bonfire'). K rate and MSC had a synergistic effect on leaf osmotic potentials. Osmotic potentials at both full and zero turgor decreased with increasing K rate and MSC. Differences between MSC and no-MSC plant osmotic potentials increased as K rate increased. Active osmotic adjustment with increasing K rate and MSC resulted in increased cellular turgor potentials. Both high K rates and MSC reduced plant gravimetric water loss on a unit leaf area basis.

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Evaluation ratings of cold injury following a freeze on December 24 & 25, 1989, showed differences among scion cultivars and rootstock. `Star Ruby' grapefruit (Citrus paradisi Macf.) and `Fallglo' citrus hybrid, a cross of Bower mandarin citrus hybrid × Temple tangor (C. temple Hort. ex Y. Tanaka) were the most severely damaged scion cultivars. `Rohde Red' valencia orange selection 472-11-43. [C. sinensis (L.) Osbeck]. was the least damaged scion cultivar. Scions budded to Cleopatra mandarin (C. reshni Hort. ex Tan.) and FL 80-18 citrumelo [C. paradisi × Poncirus trifoliata (L.) Raf.] rootstock were damaged more than on other rootstock. Scions budded to smooth flat seville (C. aurantium?) and P. trifoliata × Ridge pineapple sweet orange selection 1573-26 [C. sinensis (L.) Osbeck] had the least injury. Analysis comparing replications showed the greatest damage to be in the north side of the planting.

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Forty selections, including 37 cultivars of Hamamelis spp., were evaluated for genetic similarities using randomly amplified polymorphic DNA (RAPD) markers. Cluster analysis identified seven groups, which included three groups of H. ×intermedia cultivars, two groups of H. vernalis, and one group each of H. mollis and H. japonica. Three H. ×intermedia cultivars, `Arnold Promise', `Westerstede', and `Carmine Red', did not group closely with the other 20 cultivars of H. ×intermedia. Selections of the North American species H. vernalis were quite distinct from the Asiatic selections. However, data are presented that suggest hybridization exist between Asiatic Hamamelis spp. and H. vernalis. Genetic similarities between known half-sib families provides evidence that the cultivar pairs `Arnold Promise'—`Winter Beauty' and `Carmine Red'—`Hiltingbury' are, themselves, not likely half-sibs.

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Powdery mildew (PM) occurs worldwide and is prevalent on susceptible cultivars wherever pears are grown, causing economic losses due to russeted fruit and an increased need for fungicides. A core subset of the Pyrus germplasm collection at the USDA National Clonal Germplasm Repository in Corvallis, Ore., was evaluated for resistance to Podosphaera leucotricha, the causal agent of PM, using greenhouse and field inoculations of potted trees. The core collection consists of about 200 cultivars and species selections, representing most of the genetic diversity of pears and includes 31 Asian cultivars (ASN), 122 European cultivars (EUR), 9 EUR × ASN hybrids and 46 pear species selections. Three trees of each core accession were grafted on seedling rootstocks. In 2001–02, trees were artificially inoculated in a greenhouse, grown under conditions conducive for PM, and evaluated for symptoms. The same trees were subsequently evaluated for PM symptoms from natural field infections during 2003 and 2004. In the greenhouse, 95% of EUR and 38% of ASN were infected with PM. Average PM incidence (percent of leaves infected) in the greenhouse (8% for ASN and 30% for EUR) was much higher than incidence in the field (2% for ASN and 5% for EUR) during 2003. Symptoms were also more severe in the greenhouse, with 46% of ASN and 83% of EUR with PM symptoms having a mean PM incidence of >10%. In the field, 42% and 22% of EUR and 23% and 13% of ASN were infected with P. leucotricha in 2003 and 2004, respectively. Field infection was very low during both years, with percentage leaves infected in ASN and species selections significantly different from EUR. In the field, 6% of ASN with PM symptoms had a mean PM incidence >10% during both years, while 15% and 2% of EUR accessions with PM symptoms had a mean PM incidence >10% in 2003 and 2004 respectively. These results should be very useful to pear breeding programs to develop improved PM resistant cultivars in the future, by using accessions with consistent low PM ratings.

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Numerous isozyme systems were found to be polymorphic in witch hazel (Hamamelis spp.). However, aconitase (ACO), malate dehydrogenase, phospho-glucose isomerase (PGI), and phosphoglucomutase were most useful for identification of cultivars. From these enzyme systems, three genes were identified that control patterns of ACO (2) and PGI (1). Isozymes can be used to help verify cultivars and their simple inheritance could be useful to validate hybrids and gene flow between plants. DNA was readily extracted from young leaf tissue after grinding in liquid nitrogen and extraction in warm CTAB. DNA was amenable to amplification using polymerase chain-reaction technology. Primers (400) were screened to identify polymorphic RAPD bands. Ultimately, 19 primers were used to generate 68 RAPD markers that were reproducible. Cultivars were scored for presence or absence of the 68 markers. Genetic similarities were calculated using a Nei coefficient and clustering was conducted for more than 40 cultivars using a UPGMA program. Arbitrarily, the cultivars were assigned to seven groupings after cluster analysis. The seven classes gave one group each of H. japonica and mollis; two groups of H. vernalis; and three groups of H. ×intermedia. Clustering allowed some interpretation about relatedness among cultivars and genetic similarity data helped assign some cultivars to a particular taxa that were previously in question.

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Low and high tunnels and root-zone heating systems are proven tools in horticultural production. However, impacts of their individual and combined application on crop yield, composition, and microclimates are under-reported. We set out to enhance the record of management strategy effects on abiotic environmental conditions and cropping variables in open field and high-tunnel settings. In each setting, raised bed plots were subsurface heated (underlain by electric heating cables), aerial covered (0.8-mil, clear, vented, low tunnels), subsurface heated and aerial covered, or unheated and uncovered (control). The study was repeated four times in spring and fall seasons across 3 years in Wooster, OH. Red-leaved romaine lettuce (Lactuca sativa ‘Outredgeous’ and ‘Flagship’) was direct seeded in all plots in early October and late March and harvested after ≈4 weeks. Subsurface and aerial temperatures were monitored throughout the experiments. Here, we report primarily on treatment effects on crop microclimate conditions, including temperature and light, and related cropping variables. Subsurface and aerial temperatures varied consistently with plot microenvironment management. Relative to control plots, variability in shoot- and root-zone temperatures generally increased and decreased, respectively, with the addition of low tunnels and electric heating cables, regardless of setting. Still, the relative influence of aerial and soil temperature on crop biomass appeared to differ by setting; aerial temperature correlated most strongly with yield in the high tunnel, while the combination of aerial and root-zone temperature correlated most strongly with yield in the field. Growing degree day accumulation was least in control plots. And, the highest thermal energy to plant biomass conversion efficiency was recorded in the high tunnel. Comparing study-wide and historical climatic data collected in Wooster and other locations in the region suggests that results reported here may hold over a larger area and longer time frame in Wooster, OH.

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Low and high tunnels and root-zone heating systems are proven tools in horticultural production. However, impacts of their separate and combined application on crop yield, composition, and microclimates are underreported. We addressed these gaps in the literature by exposing lettuce (Lactuca sativa) to four microclimates established with low and high tunnels and root-zone heating during the spring and fall of 2 years in Wooster, OH. Red-leaved romaine lettuce cultivars Outredgeous and Flagship were direct-seeded into raised beds in both outdoor and high-tunnel settings in early October and late March and harvested multiple times over 4 weeks. Half of all plots in each setting were underlain by electric heating cables, and half were covered with 0.8-mil, clear, vented, low tunnels. A growing medium consisting of peat moss, compost, soil, and red clover (Trifolium pratense) hay was used, and all plots were overhead-irrigated. Soil and air temperatures were monitored throughout the experiments, which were repeated four times (2 seasons/year × 2 years). Here, we report primarily on treatment effects on crop yield and related variables. Root- and shoot-zone conditions and cultivar significantly affected leaf biomass in both settings (outdoor, high tunnel), while population was more often affected in the outdoor experiments. Microclimate main effects were more prevalent than cultivar effects or interactions. Leaf yield was greater in low-tunnel-covered and bottom-heated plots than in uncovered and unheated plots. We take these data as further evidence of the potential to alter lettuce yield through root- and shoot-zone microclimate modification, particularly in regions prone to dynamic seasonal and within-season temperature and light conditions. The data also suggest that the relative performance of low and high tunnels in the production of short-statured, quick-cycling crops during fall and spring be more thoroughly evaluated.

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Despite efforts to optimize water and nutrient inputs to Florida's vegetable and fruit crops, the sandy soils, shallow water table, and tropical climate of Florida result in nutrient leaching losses that are unavoidable. Water quantity and quality management strategies that can reduce these nutrient losses from Florida's horticultural crops were reviewed and research needs for quantifying their effectiveness were identified. The water quantity management strategies included water table management for irrigation, drainage management, detention of runoff and drainage, and summer flooding. In addition to the expected water quality benefits of these practices, potential effects on crop production and farm economics were also discussed. Watershed-scale adoption of stormwater harvesting has the potential to not only reduce the nutrient loadings but also become a source of additional income for landowners through water trading. The water quality practices included structural and managerial practices (e.g., vegetative filter strips and ditch cleaning). Key research needs for reducing the unavoidable nutrient discharges included the development of a crop-specific drainage management tool; quantification of farm and watershed-scale benefits of stormwater detention and its reuse with regards to nutrient loadings, water supply, crop production, and farm income; enhancement of hydraulic efficiency of detention areas; and effects of summer flooding and ditch maintenance and cleaning on nutrient discharges.

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Abstract

‘First Lady’ marigold (Tagetes erecta L.) was grown 3 times in each of 5 different controlled environment facilities to establish baseline growth rates for this species. Plants were grown under a standardized set of environmental conditions established with a common set of standardized instruments. Data on plants grown only once in two additional laboratories are reported for comparative purposes. The variation in growth within each laboratory was greater than the average variation among laboratories for cotyledon length and width, plant weight measurements, and 3rd leaf length but not for leaf width. The base-line growth data, based on the described procedures, can be used to compare marigold growth in other controlled environments and to provide a check on the operational characteristics of research facilities.

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