1,721,017 research outputs found
The effect of mechanical weed cultivation on crop yield and quality,disease incidence and phenology in snap bean, carrot and lettuce crops /
No full textInter-row mechanical cultivation was proposed as a supplement to or substitute for conventional weed control methods currently used in snap bean, carrot and lettuce production. Several types of cultivators were assessed and compared. The effect of mechanical cultivation on crop yield and quality was studied by counting, weighing and grading bean pods, carrot roots and lettuce heads. The effect of mechanical cultivation on disease incidence was studied by surveying fields during the season and by determining the number and weight of diseased pods, roots and heads at harvest. The relationship between the level of Cercospora blight on carrots and potential impacts on yield was also investigated by measuring plant characteristics and the amount of force needed to separate carrot foliage from root. The effect of mechanical cultivation on the phenology of snap bean flowering was studied by determining how long it took for a plant to produce 50% of its flowers and counting how many flowers and pods a plant produced. In general, mechanical cultivation did not affect normal crop production and may be used to replace or complement conventional weed control methods. There was little variation among different cultivators within one season, but cultivator effects differed among crops and from one year to the next
Alternaria alternata to control gooseweed (Sphenoclea zeylanica)
No full textA foliar pathogen identified as a member of the genus Alternaria was isolated from blighted Sphenoclea zeylanica (gooseweed) collected in 1991 from a rice field near Los Banos, Laguna, Philippines. Inoculum density, dew period, and plant height are factors influencing biocontrol of S. zeylanica with this indigenous pathogen. Significantly higher percent reductions in plant height and dry weight were obtained and all plants were killed at higher inoculum concentrations with 8 h of dew. The number, germination, and virulence of conidia were significantly affected by production techniques, temperature, light condition, and incubation period. Exposure to continuous near-ultraviolet (NUV) light at 28C stimulated sporulation on agar media and on solid substrates. Overall, the best production technique was the use of sorghum seeds using an equal quantity of sorghum seeds and water (w/v) incubated for four weeks. Another conidia production method using the sporulation medium (S-medium) technique was evaluated with the addition of 20 g L of calcium carbonate (CaCO and 2 ml of sterile distilled water. Primary 1/2 PDA at 18C in the dark produced the most virulent conidia. This technique produced conidia relatively rapid, but was labour intensive. Host range studies using 49 plant species in 40 genera representing 20 families, selected by using a modified centrifugal phylogenetic and variety strategy indicated that only S. zeylanica was susceptible in the absence and presence of supplemental dew. On the basis of morphological and cultural characteristics, pathogenicity on the host, host specificity, and the absence of a previous record of this fungal pathogen on S. zeylanica, the binomial A. alternata f. sp. sphenocleae is proposed
Spatial distribution and dose-disease relationship of airborne ascospores of Venturia inaequalis on apple
No full textApple scab is the most important disease of apples in most of the world. The disease, caused by Venturia inaequalis, is controlled by numerous fungicide applications, regardless of the presence of inoculum in the orchard. Better timing of fungicide applications could be achieved if the airborne ascospore concentration (AAC) was considered in decision making. AAC can be measured in real time using spore traps. In this project, the relationship between AAC and lesions development was studied under controlled and natural conditions for five cultivars: Empire, McIntosh, Jonagold, Royal Gala, and Spartan. Potted trees were exposed to different airborne ascospore inoculum and the corresponding AAC were measured using spore traps. The spatial distribution of ascospores was studied in a commercial apple orchard plot. The potential ascospore dose (PAD) and the AAC were measured in 40 quadrats in the spring of 1999. (Abstract shortened by UMI.
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A survey of root lesion and cereal cyst nematodes in the dryland wheat production areas of eastern Washington and resistance of pacific Northwest wheat varieties
Get PDFRoot lesion nematodes (Pratylenchus neglectus and P. thornei) and cereal cyst nematode (Heterodera avenae) are important parasites of wheat worldwide. Three studies were conducted focusing on the distribution of root lesion and cereal cyst nematodes in eastern Washington and the resistance response of spring wheat varieties to the cereal cyst nematode. The first study was conducted to estimate nematode densities in soils cropped to winter and spring cereals and spring legumes. P. neglectus and P. thornei were observed in nearly 60 percent of the sampled fields. H. avenae was observed in approximately 12 percent of the sampled fields; however, it was detected from about 45 percent of sampled fields in the annual cropping zone. Multivariate regression models were developed to determine the explanatory weather variables for Pratylenchus densities in soil. The majority of the weather variables selected in the models were precipitation variables. The second study was conducted at the Cook Agronomy Farm to determine the spatial distribution of Pratylenchus spp. in relation to crop rotation, soil and terrain attributes. Pratylenchus spp. were detected in more than 85% of the sampled sites. Classification and regression trees were developed to derive the relationship between soil and terrain variables and nematode densities. An aggregated pattern was observed, and soil organic carbon was identified as one of the most important variables to explain nematode densities. Molecular identification of Pratylenchus spp. in region-wide surveys of eastern Washington and at the Cook Agronomy Farm was conducted using species-specific primers targeting P. neglectus and P. thornei through conventional PCR. P. thornei was observed more frequently than P. neglectus in both region-wide surveys and Cook Farm, but some locations showed both species. The third field experiment was conducted to evaluate the resistance of Pacific Northwest spring wheat varieties and wheat entries carrying different Cre genes to H. avenae. Spring wheat genotypes with Cre1 gene had fewer numbers of H. avenae white females than other genotypes. However, all of the tested spring wheat varieties appear to be susceptible to H. avenae
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Field evaluation of fungal antagonists for the reduction of inoculum of Venturia inaequalis (Cke.) Wint.
No full textThe use of a biofungicide on the perfect stage of V. inaequalis on leaf litter is one potential way to reduce the number of fungicides used to control apple scab. The previous in vitro screenings of Quebec mycoflora have shown that several isolates are able to significantly reduce the primary inoculum of the pathogen. Among the screened fungi, P176A and P130A, reduced over 98% of the ascospore production and were as effective as Athelia bombacina. However, because in vitro tests are generally poor predictors of in vivo assays a re-evaluation of the antagonists was done under field conditions. Eight fungal isolates, leaf shredding, and two comparative treatments (A. bombacina, 5% urea) were applied to intact scabbed leaves in October 1994 and 1995. After the treatments, the leaves overwintered on the orchard ground until the next spring. In April, samples of treated leaves were randomly selected and placed in spore traps to collect the ejected ascospores during rainfall. Since the primary inoculum was ejected during a four-month period, antagonism was based upon ratings taken throughout the whole ejection season. To evaluate the effect of incubation conditions on the antagonistic performance we incubated separately, in vitro and in vivo, sterile leaf disks which were artificially inoculated with V. inaequalis and fungal isolates. (Abstract shortened by UMI.
Genetic mapping of Armillaria ostoyae using RAPD markers
No full textWe report here the use of RAPD-PCR (Random Amplified Polymorphic DNA - Polymerase Chain Reaction) to identify segregating loci in the haploid progeny of an Armillaria ostoyae basidiocarp and the construction of the first genetic linkage map of this fungus, one of the causal species of Armillaria Root Disease. Upon screening 75 RAPD primers, 18 were found to identify a total of 43 loci segregating with a 1 : 1 Mendelian ratio. These loci were analysed for linkage among 58 monospore progeny. The map constructed with Mapmaker (LOD = 3.0, r = 0.38) was confirmed by GMendel (LOD = 1.5, r = 0.38). This map arranged 30 loci into 6 linkage groups and 4 linkage pairs. Thirteen markers remained unlinked. Using the Kosambi mapping function the linked loci accounted for approximately 450 cM and the genome was estimated to be 1600 cM. This preliminary map covers approximately 28% of the A. ostoyae genome
The use of a fungal antagonist to reduce the initial inoculum of Gibberella zeae on wheat and corn debris /
No full textGibberella zeae (anamorph: Fusarium graminearum) is the causal agent of fusarium head blight (FHB) and maize ear rot, two major diseases of wheat and corn in Eastern Canada.In Quebec, Microsphaeropsis sp., an antagonist of Venturia inaequalis, the causal agent of apple scab, was isolated from the apple leaf litter. This fungus, well adapted to Quebec climate, can reduce the initial inoculum of V. inaequalis. FHB and Gibberella ear rot are similar to apple scab because the major inoculum source comes from melanized structures produced on crop residues. Consequently, we evaluated the potential of Microsphaeropsis sp. (isolate P130A) to inhibit ascospore production of G. zeae when applied to crop residues as post harvest or pre-planting applications. Under in vitro conditions, the antagonist significantly reduced ascospore production on wheat and corn residues, when applied prior to (82% and 92% respectively) or at the same time as the pathogen (36% and 58% respectively). Under field conditions, the antagonist had no effect on the pattern of perithecia maturation but significantly reduced the number of ascospores produced on two sampling dates, May 1998 and July 1999. (Abstract shortened by UMI.
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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