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Jianchi Chen - One of the best experts on this subject based on the ideXlab platform.
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Draft Genome Sequence of Xylella fastidiosa Pear Leaf Scorch Strain in Taiwan
Genome announcements, 2014Co-Authors: W.-l. Deng, F.-j. Jan, Chung-jan Chang, Hong Huang, Jianchi ChenAbstract:ABSTRACT The draft genome sequence of Xylella fastidiosa pear Leaf Scorch strain PLS229, isolated from the pear cultivar Hengshan (Pyrus pyrifolia) in Taiwan, is reported here. The bacterium has a genome size of 2,733,013 bp, with a G+C content of 53.1%. The PLS229 genome was annotated and has 3,259 open reading frames and 50 RNA genes.
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Management of Almond Leaf Scorch Disease: Long-Term Data on Yield, Tree Vitality, and Disease Progress
Plant disease, 2012Co-Authors: Mark S. Sisterson, Jianchi Chen, Russell L. Groves, Craig A. Ledbetter, Bradley S. Higbee, Kent M. DaaneAbstract:Sisterson, M. S., Ledbetter, C. A., Chen, J., Higbee, B. S., Groves, R. L., and Daane, K. M. 2012. Management of almond Leaf Scorch disease: Long-term data on yield, tree vitality, and disease progress. Plant Dis. 96:1037-1044. Almond Leaf Scorch disease (ALSD) has been a chronic problem for California almond growers. This disease is caused by the bacterial pathogen Xylella fastidiosa and is transmitted by xylem-feeding insects. Previous research suggested that retaining, rather than roguing, ALSD-affected trees may be more economically beneficial because ALSD-affected trees produced a reasonable yield and did not die over a 3-year period. Because almond orchards are kept in production for approximately 25 years, longer-term data are needed to fully evaluate the merits of retaining ALSD-affected trees. Extension of yield evaluations from 3 to 5 years demonstrated that yield loss due to ALSD was consistent over 5 years, with yields of ALSD-affected trees reduced by 20 and 40% compared with unaffected trees for ‘Nonpareil’ and ‘Sonora’, respectively. To assess risk of ALSD-affected trees serving as a source of inocula for secondary (tree-to-tree) spread and to evaluate vitality of ALSD-affected trees, previous surveys of two orchards were extended from 3 to 6 or 7 years. The relationship between disease incidence (percentage of trees infected) and survey year was linear for all cultivars examined at both orchards. Furthermore, at each orchard, the spatial location of infections detected after the first survey was random with respect to the spatial location of infections identified during the first survey, suggesting that ALSD-affected trees retained in orchards did not serve as a source for secondary spread. Over the 6- to 7-year study period, death of ALSD-affected trees was rare, with only 9% of ALSD-affected trees dying. Because orchards used in this study had relatively high disease incidence, 61 orchards containing Sonora were surveyed to determine typical levels of ALSD incidence. ALSD was widespread, with at least one infected tree in 56% of orchards surveyed, but incidence was typically low (mean incidence = 0.47%). Collectively, the results suggest that retaining ALSD-affected trees may be economically beneficial in older orchards.
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Phenology of Xylella fastidiosa and Its Vector Around California Almond Nurseries: An Assessment of Plant Vulnerability to Almond Leaf Scorch Disease.
Plant disease, 2012Co-Authors: Rodrigo Krugner, Jianchi Chen, Craig A. Ledbetter, Anil ShresthaAbstract:Abstract Management of almond Leaf Scorch disease requires knowledge of all possible infection pathways. The disease is caused by the xylem-limited bacterium Xylella fastidiosa, which is transmitted by several species of sharpshooters. The objectives of this research were to elucidate the fate of bacteria in planta after inoculations in almond nursery plants and to determine patterns of insect vector population dynamics and temporal distribution of X. fastidiosa–infected plants relative to host plant assemblages in habitats surrounding commercial nurseries. In an experimental nursery, disease incidence was markedly affected by rootstock type. Prior to bud grafting, ‘Nemaguard’ rootstock seedlings were not susceptible to bacterial infection. After bud grafting with a susceptible scion (‘Sonora’), scions were susceptible to infection regardless of rootstock genotype. Surveys near commercial nurseries revealed that only habitats with permanent grass cover sustained vector populations throughout the season. A...
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whole genome sequences of two xylella fastidiosa strains m12 and m23 causing almond Leaf Scorch disease in california
Journal of Bacteriology, 2010Co-Authors: Jianchi Chen, Gary Xie, Shunsheng Han, Olga Chertkov, David Sims, Edwin L. CiveroloAbstract:Xylella fastidiosa is a Gram-negative plant-pathogenic bacterium causing many economically important diseases, including almond Leaf Scorch disease (ALSD) in California. Genome information greatly facilitates research on this nutritionally fastidious organism. Here we report the complete genome sequences of two ALSD strains of this bacterium, M12 and M23.
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Effects of Almond Leaf Scorch Disease on Almond Yield: Implications for Management
Plant disease, 2008Co-Authors: Mark S. Sisterson, Jianchi Chen, Edwin L. Civerolo, Mario Viveros, Craig A. Ledbetter, Russell L. GrovesAbstract:Almond Leaf Scorch (ALS) disease has been present in California's almond-growing regions for over 60 years. This disease is caused by the bacterium Xylella fastidiosa and the pathogen is vectored by xylem-feeding sharpshooters and spittlebugs. Currently, there are no effective management techniques that prevent trees from becoming infected. Within affected orchards throughout California's Central Valley, disease incidence and the risk of tree-to-tree spread appears to be low. Consequently, the decision to remove or keep infected trees depends on lost productivity. We compared yield and vitality between infected and uninfected almond for cvs. Sonora and Nonpareil. Sonora was examined at three sites over 3 years and Nonpareil was examined at one site over 2 years. Yields of ALS-affected trees were significantly lower for both cultivars, although yield losses of Sonora were proportionally greater than those of Nonpareil. Yields of infected trees did not decline incrementally over years; rather, they fluctuated similarly to those of uninfected trees. In addition, no infected trees died during the course of the study. These results are in direct contrast to previous anecdotal reports which suggest that yields of infected trees incrementally decline and infected trees eventually die. A simple economic model was developed to determine conditions under which rouging infected trees would increase returns. Based on the model, orchard age, yield loss due to infection, and the value of a maximally producing almond tree should be considered when deciding to remove ALS-affected trees.
Russell L. Groves - One of the best experts on this subject based on the ideXlab platform.
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Population Structure of Xylella fastidiosa Associated with Almond Leaf Scorch Disease in the San Joaquin Valley of California
Phytopathology, 2015Co-Authors: Hong Lin, Edwin L. Civerolo, Sajedul Islam, Juan C. Cabrera-la Rosa, Russell L. GrovesAbstract:Lin, H., Islam, M. S., Rosa, J. C. C.-L., Civerolo, E. L., and Groves, R. L. 2015. Population structure of Xylella fastidiosa associated with almond Leaf Scorch disease in the San Joaquin Valley of California. Phytopathology 105:825-832. Xylella fastidiosa causes disease in many commercial crops, including almond Leaf Scorch (ALS) disease in susceptible almond (Prunus dulcis). In this study, genetic diversity and population structure of X. fastidiosa associated with ALS disease were evaluated. Isolates obtained from two almond orchards in Fresno and Kern County in the San Joaquin Valley of California were analyzed for two successive years. Multilocus simple-sequence repeat (SSR) analysis revealed two major genetic clusters that were associated with two host cultivars, ‘Sonora’ and ‘Nonpareil’, respectively, regardless of the year of study or location of the orchard. These relationships suggest that host cultivar selection and adaptation are major driving forces shaping ALS X. fastidiosa population structure in the San Joaquin Valley. This finding will provide insight into understanding pathogen adaptation and host selection in the context of ALS disease dynamics. Additional keywords: annual variation.
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Population Structure of Xylella fastidiosa Associated with Almond Leaf Scorch Disease in the San Joaquin Valley of California
Phytopathology, 2015Co-Authors: Hong Lin, Edwin L. Civerolo, Sajedul Islam, Juan C. Cabrera-la Rosa, Russell L. GrovesAbstract:Xylella fastidiosa causes disease in many commercial crops, including almond Leaf Scorch (ALS) disease in susceptible almond (Prunus dulcis). In this study, genetic diversity and population structure of X. fastidiosa associated with ALS disease were evaluated. Isolates obtained from two almond orchards in Fresno and Kern County in the San Joaquin Valley of California were analyzed for two successive years. Multilocus simple-sequence repeat (SSR) analysis revealed two major genetic clusters that were associated with two host cultivars, ‘Sonora’ and ‘Nonpareil’, respectively, regardless of the year of study or location of the orchard. These relationships suggest that host cultivar selection and adaptation are major driving forces shaping ALS X. fastidiosa population structure in the San Joaquin Valley. This finding will provide insight into understanding pathogen adaptation and host selection in the context of ALS disease dynamics.
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Management of Almond Leaf Scorch Disease: Long-Term Data on Yield, Tree Vitality, and Disease Progress
Plant disease, 2012Co-Authors: Mark S. Sisterson, Jianchi Chen, Russell L. Groves, Craig A. Ledbetter, Bradley S. Higbee, Kent M. DaaneAbstract:Sisterson, M. S., Ledbetter, C. A., Chen, J., Higbee, B. S., Groves, R. L., and Daane, K. M. 2012. Management of almond Leaf Scorch disease: Long-term data on yield, tree vitality, and disease progress. Plant Dis. 96:1037-1044. Almond Leaf Scorch disease (ALSD) has been a chronic problem for California almond growers. This disease is caused by the bacterial pathogen Xylella fastidiosa and is transmitted by xylem-feeding insects. Previous research suggested that retaining, rather than roguing, ALSD-affected trees may be more economically beneficial because ALSD-affected trees produced a reasonable yield and did not die over a 3-year period. Because almond orchards are kept in production for approximately 25 years, longer-term data are needed to fully evaluate the merits of retaining ALSD-affected trees. Extension of yield evaluations from 3 to 5 years demonstrated that yield loss due to ALSD was consistent over 5 years, with yields of ALSD-affected trees reduced by 20 and 40% compared with unaffected trees for ‘Nonpareil’ and ‘Sonora’, respectively. To assess risk of ALSD-affected trees serving as a source of inocula for secondary (tree-to-tree) spread and to evaluate vitality of ALSD-affected trees, previous surveys of two orchards were extended from 3 to 6 or 7 years. The relationship between disease incidence (percentage of trees infected) and survey year was linear for all cultivars examined at both orchards. Furthermore, at each orchard, the spatial location of infections detected after the first survey was random with respect to the spatial location of infections identified during the first survey, suggesting that ALSD-affected trees retained in orchards did not serve as a source for secondary spread. Over the 6- to 7-year study period, death of ALSD-affected trees was rare, with only 9% of ALSD-affected trees dying. Because orchards used in this study had relatively high disease incidence, 61 orchards containing Sonora were surveyed to determine typical levels of ALSD incidence. ALSD was widespread, with at least one infected tree in 56% of orchards surveyed, but incidence was typically low (mean incidence = 0.47%). Collectively, the results suggest that retaining ALSD-affected trees may be economically beneficial in older orchards.
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Effects of Almond Leaf Scorch Disease on Almond Yield: Implications for Management
Plant disease, 2008Co-Authors: Mark S. Sisterson, Jianchi Chen, Edwin L. Civerolo, Mario Viveros, Craig A. Ledbetter, Russell L. GrovesAbstract:Almond Leaf Scorch (ALS) disease has been present in California's almond-growing regions for over 60 years. This disease is caused by the bacterium Xylella fastidiosa and the pathogen is vectored by xylem-feeding sharpshooters and spittlebugs. Currently, there are no effective management techniques that prevent trees from becoming infected. Within affected orchards throughout California's Central Valley, disease incidence and the risk of tree-to-tree spread appears to be low. Consequently, the decision to remove or keep infected trees depends on lost productivity. We compared yield and vitality between infected and uninfected almond for cvs. Sonora and Nonpareil. Sonora was examined at three sites over 3 years and Nonpareil was examined at one site over 2 years. Yields of ALS-affected trees were significantly lower for both cultivars, although yield losses of Sonora were proportionally greater than those of Nonpareil. Yields of infected trees did not decline incrementally over years; rather, they fluctuated similarly to those of uninfected trees. In addition, no infected trees died during the course of the study. These results are in direct contrast to previous anecdotal reports which suggest that yields of infected trees incrementally decline and infected trees eventually die. A simple economic model was developed to determine conditions under which rouging infected trees would increase returns. Based on the model, orchard age, yield loss due to infection, and the value of a maximally producing almond tree should be considered when deciding to remove ALS-affected trees.
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Colony morphology of Xylella fastidiosa almond Leaf Scorch strains
Canadian Journal of Plant Pathology, 2007Co-Authors: Jianchi Chen, Edwin L. Civerolo, Russell L. Groves, Yiwei Zheng, Mario Viveros, Mark FreemanAbstract:Xylella fastidiosa is the causal agent of almond Leaf Scorch disease (ALSD), which is currently reemerging in California as a potential threat to almond (Prunus dulcis) production. We previously reported the presence of different colony morphotypes of X. fastidiosa ALSD strains on periwinkle wilt medium solidified with Gelrite and their association with genotypes or pathotypes after a low number of serial transfers. The morphotypes could be differentiated by single nucleotide polymorphisms and were classified as A- and G-genotypes. The stability of colony morphology was not studied. Yet, it is an important issue in the bacterial characterization. In this project, we evaluated the variations of colony morphology through 14 subculture passages. The G-genotype strains were consistently (>99%) associated with smooth colony morphotypes. Similarly, A-genotype strains were consistently associated with rough colony morphotypes. Rough A-genotype strains reversed to smooth colony variants at a low frequency suggest...
Edwin L. Civerolo - One of the best experts on this subject based on the ideXlab platform.
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Population Structure of Xylella fastidiosa Associated with Almond Leaf Scorch Disease in the San Joaquin Valley of California
Phytopathology, 2015Co-Authors: Hong Lin, Edwin L. Civerolo, Sajedul Islam, Juan C. Cabrera-la Rosa, Russell L. GrovesAbstract:Lin, H., Islam, M. S., Rosa, J. C. C.-L., Civerolo, E. L., and Groves, R. L. 2015. Population structure of Xylella fastidiosa associated with almond Leaf Scorch disease in the San Joaquin Valley of California. Phytopathology 105:825-832. Xylella fastidiosa causes disease in many commercial crops, including almond Leaf Scorch (ALS) disease in susceptible almond (Prunus dulcis). In this study, genetic diversity and population structure of X. fastidiosa associated with ALS disease were evaluated. Isolates obtained from two almond orchards in Fresno and Kern County in the San Joaquin Valley of California were analyzed for two successive years. Multilocus simple-sequence repeat (SSR) analysis revealed two major genetic clusters that were associated with two host cultivars, ‘Sonora’ and ‘Nonpareil’, respectively, regardless of the year of study or location of the orchard. These relationships suggest that host cultivar selection and adaptation are major driving forces shaping ALS X. fastidiosa population structure in the San Joaquin Valley. This finding will provide insight into understanding pathogen adaptation and host selection in the context of ALS disease dynamics. Additional keywords: annual variation.
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Population Structure of Xylella fastidiosa Associated with Almond Leaf Scorch Disease in the San Joaquin Valley of California
Phytopathology, 2015Co-Authors: Hong Lin, Edwin L. Civerolo, Sajedul Islam, Juan C. Cabrera-la Rosa, Russell L. GrovesAbstract:Xylella fastidiosa causes disease in many commercial crops, including almond Leaf Scorch (ALS) disease in susceptible almond (Prunus dulcis). In this study, genetic diversity and population structure of X. fastidiosa associated with ALS disease were evaluated. Isolates obtained from two almond orchards in Fresno and Kern County in the San Joaquin Valley of California were analyzed for two successive years. Multilocus simple-sequence repeat (SSR) analysis revealed two major genetic clusters that were associated with two host cultivars, ‘Sonora’ and ‘Nonpareil’, respectively, regardless of the year of study or location of the orchard. These relationships suggest that host cultivar selection and adaptation are major driving forces shaping ALS X. fastidiosa population structure in the San Joaquin Valley. This finding will provide insight into understanding pathogen adaptation and host selection in the context of ALS disease dynamics.
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whole genome sequences of two xylella fastidiosa strains m12 and m23 causing almond Leaf Scorch disease in california
Journal of Bacteriology, 2010Co-Authors: Jianchi Chen, Gary Xie, Shunsheng Han, Olga Chertkov, David Sims, Edwin L. CiveroloAbstract:Xylella fastidiosa is a Gram-negative plant-pathogenic bacterium causing many economically important diseases, including almond Leaf Scorch disease (ALSD) in California. Genome information greatly facilitates research on this nutritionally fastidious organism. Here we report the complete genome sequences of two ALSD strains of this bacterium, M12 and M23.
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Effects of Almond Leaf Scorch Disease on Almond Yield: Implications for Management
Plant disease, 2008Co-Authors: Mark S. Sisterson, Jianchi Chen, Edwin L. Civerolo, Mario Viveros, Craig A. Ledbetter, Russell L. GrovesAbstract:Almond Leaf Scorch (ALS) disease has been present in California's almond-growing regions for over 60 years. This disease is caused by the bacterium Xylella fastidiosa and the pathogen is vectored by xylem-feeding sharpshooters and spittlebugs. Currently, there are no effective management techniques that prevent trees from becoming infected. Within affected orchards throughout California's Central Valley, disease incidence and the risk of tree-to-tree spread appears to be low. Consequently, the decision to remove or keep infected trees depends on lost productivity. We compared yield and vitality between infected and uninfected almond for cvs. Sonora and Nonpareil. Sonora was examined at three sites over 3 years and Nonpareil was examined at one site over 2 years. Yields of ALS-affected trees were significantly lower for both cultivars, although yield losses of Sonora were proportionally greater than those of Nonpareil. Yields of infected trees did not decline incrementally over years; rather, they fluctuated similarly to those of uninfected trees. In addition, no infected trees died during the course of the study. These results are in direct contrast to previous anecdotal reports which suggest that yields of infected trees incrementally decline and infected trees eventually die. A simple economic model was developed to determine conditions under which rouging infected trees would increase returns. Based on the model, orchard age, yield loss due to infection, and the value of a maximally producing almond tree should be considered when deciding to remove ALS-affected trees.
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Colony morphology of Xylella fastidiosa almond Leaf Scorch strains
Canadian Journal of Plant Pathology, 2007Co-Authors: Jianchi Chen, Edwin L. Civerolo, Russell L. Groves, Yiwei Zheng, Mario Viveros, Mark FreemanAbstract:Xylella fastidiosa is the causal agent of almond Leaf Scorch disease (ALSD), which is currently reemerging in California as a potential threat to almond (Prunus dulcis) production. We previously reported the presence of different colony morphotypes of X. fastidiosa ALSD strains on periwinkle wilt medium solidified with Gelrite and their association with genotypes or pathotypes after a low number of serial transfers. The morphotypes could be differentiated by single nucleotide polymorphisms and were classified as A- and G-genotypes. The stability of colony morphology was not studied. Yet, it is an important issue in the bacterial characterization. In this project, we evaluated the variations of colony morphology through 14 subculture passages. The G-genotype strains were consistently (>99%) associated with smooth colony morphotypes. Similarly, A-genotype strains were consistently associated with rough colony morphotypes. Rough A-genotype strains reversed to smooth colony variants at a low frequency suggest...
Qi Huang - One of the best experts on this subject based on the ideXlab platform.
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Genome Sequence of a Xylella fastidiosa Strain Causing Sycamore Leaf Scorch Disease in Virginia
Genome announcements, 2014Co-Authors: Wei Guan, Jonathan Shao, Robert E. Davis, Tingchang Zhao, Qi HuangAbstract:ABSTRACT Xylella fastidiosa causes bacterial Leaf Scorch in landscape trees including sycamore. We determined the draft genome of X. fastidiosa strain Sy-Va, isolated in Virginia from a sycamore tree displaying Leaf Scorch symptoms. The Sy-VA genome contains 2,477,829 bp, and has a G+C content of 51.64 mol%.
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Genome Sequence of a Xylella fastidiosa Strain Causing Mulberry Leaf Scorch Disease in Maryland
Genome announcements, 2014Co-Authors: Wei Guan, Jonathan Shao, Tingchang Zhao, Qi HuangAbstract:ABSTRACT Xylella fastidiosa causes bacterial Leaf Scorch in landscape trees, including mulberry. We determined the draft genome of the mulberry strain Mul-MD in order to gain a better understanding of the molecular basis of strain divergence, host specificity, nutrient requirements, and pathogenicity, as well as to develop genome-based specific detection methods.
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A TaqMan-based real time PCR assay for specific detection and quantification of Xylella fastidiosa strains causing bacterial Leaf Scorch in oleander.
Journal of microbiological methods, 2012Co-Authors: Wei Guan, Jonathan Shao, Robert E. Davis, Tingchang Zhao, Raghuwinder Singh, Qi HuangAbstract:Abstract A TaqMan-based real-time PCR assay was developed for specific detection of strains of X . fastidiosa causing oleander Leaf Scorch. The assay uses primers WG-OLS-F1 and WG-OLS-R1 and the fluorescent probe WG-OLS-P1, designed based on unique sequences found only in the genome of oleander strain Ann1. The assay is specific, allowing detection of only oleander-infecting strains, not other strains of X . fastidiosa nor other plant-associated bacteria tested. The assay is also sensitive, with a detection limit of 10.4 fg DNA of X . fastidiosa per reaction in vitro and in planta . The assay can also be applied to detect low numbers of X . fastidiosa in insect samples, or further developed into a multiplex real-time PCR assay to simultaneously detect and distinguish diverse strains of X . fastidiosa that may occupy the same hosts or insect vectors. Specific and sensitive detection and quantification of oleander strains of X . fastidiosa should be useful for disease diagnosis, epidemiological studies, management of oleander Leaf Scorch disease, and resistance screening for oleander shrubs.
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Specific Detection and Identification of Xylella fastidiosa Strains Causing Oleander Leaf Scorch Using Polymerase Chain Reaction
Current microbiology, 2008Co-Authors: Qi HuangAbstract:A pair of PCR primers, QH-OLS05/QH-OLS08 specific for strains of Xylella fastidiosa causing oleander Leaf Scorch was developed. The primers were designed according to a DNA sequence of a randomly amplified polymorphic DNA (RAPD)-polymerase chain reaction (PCR) product unique to oleander strains. The PCR assay using primer pair QH-OLS05/QH-OLS08 allowed quick and simple detection and identification of oleander strains in cultured bacterium and infected plant samples. The assay also can be applied to insect samples. Specific detection and identification of oleander strains of X. fastidiosa by PCR is useful for epidemiologic and etiologic studies of oleander Leaf Scorch by identifying what plants and insect vectors harbor or carry this particular strain of X. fastidiosa, especially in locations where mixed natural infections by oleander and other strains of X. fastidiosa occur.
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Association of Xylella fastidiosa with Leaf Scorch in Japanese beech bonsai
Canadian Journal of Plant Pathology, 2003Co-Authors: Qi Huang, John S. HartungAbstract:A disorder was recently observed in a 76-year-old Japanese beech (Fagus crenata) bonsai with symptoms including marginal Scorch of leaves bordered by a chlorotic halo, as well as a premature Leaf browning and defoliation. Leaf midrib extracts from the affected bonsai reacted with an antiserum specific to Xylella fastidiosa in an enzyme-linked immunosorbent assay. When the total DNA from the Leaf midribs of the affected bonsai was extracted and subjected to polymerase chain reaction (PCR) with primers specific to X. fastidiosa, a 472-bp PCR product was detected. The PCR product was confirmed to be the predicted X. fastidiosa product by sequencing and sequence comparison with the reported genomic sequence of X. fastidiosa. Enzyme-linked immunosorbent and PCR assays of Leaf midrib extracts of a symptomless Japanese beech tree were negative. This is the first report of X. fastidiosa associated with Leaf Scorch in high-valued bonsai and in beech.
P. H. Jerie - One of the best experts on this subject based on the ideXlab platform.
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Effect of intensity and duration of twospotted spider mite (Acari: Tetranychidae) infestation and water stress on Leaf Scorch damage of Bartlett' pear
Journal of Economic Entomology, 1994Co-Authors: S. C. Mcnab, D. G. Williams, P. H. JerieAbstract:A field experiment was conducted in 1990-1992 to investigate the relationship between the level and duration of twospotted spider mite, Tetranychus urticae Koch, infestation and the development of Leaf Scorch damage on ‘Bartlett’ (‘William Bon Chretien’) pear trees. The effect of water stress on the development of T. urticae Leaf Scorch damage was also investigated. The development of Leaf Scorch damage was strongly related to indices that combine the level and duration of mite infestation. Water stress was an important determinant of the severity of Leaf Scorch damage that developed. A strong correlation ( P < 0.001) occurred between the mean number of mites per Leaf and the proportion of leaves infested with mites. Mean mites per Leaf counts and the percentage of leaves infested were converted into cumulative mite days (CMD) and cumulative percentage Leaf infested days (CLID), respectively. The level of both CMD ( P < 0.01) and CLID ( P < 0.01) and the development of Leaf Scorch damage on individual ‘Bartlett’ pear trees were closely related. Water stress significantly increased the level of Leaf Scorch damage that developed at given levels of mite days ( P < 0.05) and Leaf infested days ( P < 0.01). In one season only, there was an slight increase ( P < 0.05) in mite populations on water stressed trees compared with well irrigated trees. A Simple damage threshold of 5-10% Scorched Leaf area would correspond to levels of ≍100-150 mite days or 1,500-2,500 Leaf infested days accumulated in a season.
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Flowering, fruit set, and yield response of 'Bartlett' pear to Leaf-Scorch damage by twospotted spider mite (Acari: Tetranychidae).
Journal of Economic Entomology, 1993Co-Authors: S. C. Mcnab, P. H. JerieAbstract:The effect of Leaf Scorch and defoliation caused by twos potted spider mite, Tetranychus urticae Koch, was investigated on flower production, fruit set, fruit yield, and mean fruit weight of ‘Bartlett’ pear. The level of Leaf Scorch and defoliation was estimated in autumn, and the number of flowers per flower cluster, fruit set, and fruit yield were determined in the following season. The number of flowers per flower cluster was significantly reduced ( P < 0.05) by Leaf Scorch and defoliation in the previous summer, but the response was only slight with flower clusters having approximately five flowers per flower cluster. Fruit set per flower cluster, gross fruit yield, and the yield of fruit suitable for canning were Significantly reduced ( P < 0.01) by Leaf Scorch and defoliation in the previous year. On trees with 80% Leaf Scorch and defoliation in the previous summer, gross yield and the yield of fruit suitable for canning were reduced to approximately a third of the level determined for trees that experienced no Leaf Scorch and defoliation in the previous year. Mean fruit weight increased only marginally as fruit density per square meter of planted area decreased, indicating that Leaf-Scorch damage from twos potted mite may affect fruit growth of ‘Bartlett’ pear in the following year. Fruit set was not responsive to Leaf-Scorch damage in the second and third years after Leaf damage had occurred. The effect of these results on a damage threshold is discussed.
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Leaf Scorch Responses of ‘Sensation’ and ‘Bartlett’ Pear to Two spotted Spider Mite (Acari: Tetranychidae)
Journal of Economic Entomology, 1991Co-Authors: S. C. Mcnab, P. H. JerieAbstract:The effect of 0,2,5, and 10 adult female two spotted spider mites, Tetranychw urticae Koch, per Leaf on the percentage of Leaf area affected by Leaf Scorch and Leaf stippling was investigated in two pear cultivars, ‘Bartlett’ (‘William Bon Chretien’) and ‘Sensation’, a red ‘Bartlett’ mutation. The percentage of Leaf area affected by stippling increased ( P 0.05) difference in the Leaf-stippling response of the two cultivars. The percentage of Leaf area affected by Scorch was found to significantly increase ( P < 0.01) on ‘Bartlett’ leaves with increasing mite density; virtually no Leaf Scorch was observed on ‘Sensation’ leaves. Mite densities were similar at each treatment level for ‘Bartlett’ and ‘Sensation’ leaves. This indicates a tolerance to Leaf Scorch resulting from two spotted spider mite feeding in the ‘Sensation’ variety.