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Ramsey S. Lewis - One of the best experts on this subject based on the ideXlab platform.
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adaptation of Phytophthora nicotianae to multiple sources of partial resistance in tobacco
Plant Disease, 2021Co-Authors: Jing Jin, Ramsey S. Lewis, Kestrel Lannon Mccorkle, Vicki Cornish, Ignazio Carbone, David H ShewAbstract:Host resistance is an important tool in the management of black shank disease of tobacco. While race development leads to rapid loss of single-gene resistance, the adaptation by Phytophthora nicotianae to sources of partial resistance from Beinhart 1000, Florida 301, and the Wz gene region introgressed from Nicotiana rustica is poorly characterized. In greenhouse environments, host genotypes with QTLs conferring resistance from multiple sources were initially inoculated with an aggressive isolate of race 0 or race 1 of P. nicotianae. The most aggressive isolate was selected after each of six host generations to inoculate the next generation of plants. The race 0 isolate demonstrated a continuous gradual increase in disease severity and percent root rot on all sources of resistance except the genotype K 326 Wz/--, where a large increase in both was observed between generations two and three. Adaptation by the race 0 isolate on Beinhart 1000 represents the first report of adaptation to this genotype by P. nicotianae. The race 1 isolate did not exhibit significant increases in aggressiveness over generations, but also exhibited a large increase in aggressiveness on K 326 Wz/-- between generations 3 and 4. Molecular characterization of isolates recovered during selection was completed using ddRADseq, but no polymorphisms were associated with the observed changes in aggressiveness. The rapid adaptation to Wz resistance and the gradual adaptation to other QTLs highlights the need to study the nature of Wz resistance and for conducting field studies on efficacy of resistance-gene rotation for disease management.
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evaluating diverse systems of tobacco genetic resistance to Phytophthora nicotianae in yunnan china
Plant Pathology, 2019Co-Authors: Jianmin Zeng, Jessica M Nifong, Dunhuang Fang, Yong Liu, Changjun Huang, Ramsey S. LewisAbstract:Black shank, caused by the soilborne pathogen Phytophthora nicotianae, is one of the most devastating diseases affecting tobacco production in China. The most effective strategy for reducing economic loss from this pathogen is development and use of resistant tobacco varieties. Multiple sources and systems of resistance have been developed in the Western Hemisphere; however, populations of P. nicotianae are variable around the world, including the predominance of different races. Different P. nicotianae isolates may react differently on tobacco plants with different systems of resistance, a possibility that could complicate the breeding of cultivars with resistance that is effective in different tobacco production regions worldwide. The objective of this research was to evaluate an array of tobacco germplasm possessing different systems of genetic resistance to black shank disease in tobacco‐growing regions of Yunnan, China. Resistance types included simply inherited resistance mechanisms introgressed from wild Nicotiana relatives and polygenic partial resistance systems of N. tabacum origin. The loci of Wz exhibited high level resistance to black shank in the five diverse disease environments in Yunnan, China. K326 Php/−Wz/− genotype and Beinhart 1000 exhibited the greatest levels of resistance in both 2015 and 2016. Field observed results for 13 tobacco genotypes were highly correlated with those tested in growth chamber evaluation. These findings suggest that both Wz− and Beinhart 1000‐mediated resistance have important commercial value in flue‐cured tobacco breeding programmes in China. Cultivars developed for black shank resistance in China may also have utility in other tobacco‐growing areas.
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identification and validation of snp markers associated with wz mediated Phytophthora nicotianae resistance in nicotiana tabacum l
Molecular Breeding, 2019Co-Authors: Rui Shi, Hannah Hubert, Abigail Dexterboone, Jianmin Zeng, Sheri P Kernodle, Ramsey S. LewisAbstract:A chromosome segment designated as Wz found to positively affect resistance of to black shank disease caused by Phytophthora nicotianae was previously introgressed from Nicotiana rustica into cultivated tobacco (N. tabacum). DNA markers associated with this region can aid in efforts to pyramid multiple mechanisms of black shank resistance into single new tobacco cultivars. In order to identify DNA markers associated with Wz, we generated RNA-seq data from roots of nearly isogenic lines (NILs) differing for the presence/absence of the alien genomic region. Analysis of SNPs, INDELs, and differentially expressed genes that distinguished the NILs suggested that the N. rustica Wz introgression replaced an approximately 65 Mb region of N. tabacum chromosome 19. The utility of a subset of derived Kompetitive Allele Specific PCR (KASP) and Cleaved Amplified Polymorphic Sequence (CAPS) markers for predicting the presence of Wz was verified using segregating populations and F3:4 families that were evaluated for field black shank resistance. The new markers are useful for overall efforts to develop tobacco cultivars containing novel gene combinations affecting soil-borne pathogen resistance.
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genetic analysis of phn7 1 a major qtl conferring partial resistance to Phytophthora nicotianae in nicotiana tabacum
Molecular Breeding, 2019Co-Authors: Justin M, Jessica M Nifong, Crystal Heim, Matt Humphry, Ramsey S. LewisAbstract:The oomycete Phytophthora nicotianae is one of the most economically important pathogens affecting tobacco (Nicotiana tabacum L.). Genetic resistance is a preferred means of managing damage caused by Phytophthora, and genes conferring partial resistance are likely to be more durable over time than those controlling immunity. Characterization of specific genetic variability controlling partial disease resistance may aid the development of long-term strategies for minimizing crop plant disease loss. Previous mapping studies identified a quantitative trait locus (QTL) designated as Phn7.1 controlling partial P. nicotianae resistance. Favorable alleles at this QTL have been identified in cigar tobacco cultivars ‘Beinhart 1000’ and ‘Florida 301,’ and were thought to also be present in most modern elite US flue-cured tobacco germplasm. To gain increased insight of the location and effect of Phn7.1, this QTL was mapped using an increased number of molecular markers (SNPs) in the genomic region of interest. A series of near isogenic lines (NILs) and sub-NILs carrying the Phn7.1-associated genomic region introgressed from Beinhart 1000 in the genetic background of susceptible variety Hicks were developed and evaluated. The region was found to have an additive effect on resistance and the corresponding QTL was localized to within a genetic interval of approximately 3 cM. Genotyping of historical materials with Phn7.1-associated SNP markers strongly suggests that the favorable Phn7.1 allele(s) is present in most modern US flue-cured cultivars and absent in early predecessor germplasm. Information from this study may be useful in marker-assisted selection and for identification of Phn7.1 candidate genes in future investigations.
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characterization of Phytophthora nicotianae resistance conferred by the introgressed nicotiana rustica region wz in flue cured tobacco
Plant Disease, 2017Co-Authors: Kestrel Lannon Mccorkle, Ramsey S. Lewis, Katherine E Drakestowe, David H ShewAbstract:Black shank, caused by Phytophthora nicotianae, is one of the most important diseases affecting tobacco worldwide and is primarily managed through use of host resistance. An additional source of re...
David H Shew - One of the best experts on this subject based on the ideXlab platform.
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adaptation of Phytophthora nicotianae to multiple sources of partial resistance in tobacco
Plant Disease, 2021Co-Authors: Jing Jin, Ramsey S. Lewis, Kestrel Lannon Mccorkle, Vicki Cornish, Ignazio Carbone, David H ShewAbstract:Host resistance is an important tool in the management of black shank disease of tobacco. While race development leads to rapid loss of single-gene resistance, the adaptation by Phytophthora nicotianae to sources of partial resistance from Beinhart 1000, Florida 301, and the Wz gene region introgressed from Nicotiana rustica is poorly characterized. In greenhouse environments, host genotypes with QTLs conferring resistance from multiple sources were initially inoculated with an aggressive isolate of race 0 or race 1 of P. nicotianae. The most aggressive isolate was selected after each of six host generations to inoculate the next generation of plants. The race 0 isolate demonstrated a continuous gradual increase in disease severity and percent root rot on all sources of resistance except the genotype K 326 Wz/--, where a large increase in both was observed between generations two and three. Adaptation by the race 0 isolate on Beinhart 1000 represents the first report of adaptation to this genotype by P. nicotianae. The race 1 isolate did not exhibit significant increases in aggressiveness over generations, but also exhibited a large increase in aggressiveness on K 326 Wz/-- between generations 3 and 4. Molecular characterization of isolates recovered during selection was completed using ddRADseq, but no polymorphisms were associated with the observed changes in aggressiveness. The rapid adaptation to Wz resistance and the gradual adaptation to other QTLs highlights the need to study the nature of Wz resistance and for conducting field studies on efficacy of resistance-gene rotation for disease management.
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components of aggressiveness in Phytophthora nicotianae during adaptation to multiple sources of partial resistance in tobacco
Plant Disease, 2021Co-Authors: Jing Jin, David H ShewAbstract:Black shank is a devastating disease of tobacco caused by Phytophthora nicotianae. Host resistance has been an integral part of black shank management but after the loss of Php single-gene resistance following its widespread deployment in the 1990s, growers have relied on varieties with varying levels of partial resistance. Partial resistance is effective in suppressing disease, but continued exposure can result in an increase in pathogen aggressiveness that threatens durability of the resistance to P. nicotianae. Aggressiveness components in P. nicotianae were characterized following adaptation on two sources of partial resistance, Fla 301 and the Wz genomic region from Nicotiana rustica. An aggressive isolate of the two major races of P. nicotianae, race 0 and race 1, was adapted for either one/two or five/six generations on the two resistance sources, giving four sets of isolates based on race, number of generations of adaptation, and source of resistance. Across the four sets of isolates, adapted isolates infected higher proportions of tobacco root tips, produced more sporangia per infected root tip, and caused larger lesions than their respective nonadapted isolates of the same race and from the same resistance source. Adapted isolates also produced more aggressive zoospore progeny than the nonadapted isolates. Adaptation to partial resistance involves multiple aggressiveness components and results in the increased aggressiveness observed for P. nicotianae. These results improve our knowledge on the nature of P. nicotianae adaptation to partial resistance in tobacco and indicate that different resistance sources are likely to select for similar aggressiveness components in the pathogen.
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characterization of the black shank pathogen Phytophthora nicotianae across north carolina tobacco production areas
Plant Disease, 2017Co-Authors: Courtney Gallup, Kestrel Lannon Mccorkle, Kelly L Ivors, David H ShewAbstract:Black shank disease of tobacco, caused by the oomycete Phytophthora nicotianae, is a major threat to production in the United States and tobacco-producing areas worldwide. In a statewide survey of North Carolina, the rapid shift from race 0 to race 1 was documented. Collected pathogen isolates were characterized phenotypically for mating type and mefenoxam sensitivity, and genotypically by comparing sequences from three cytoplasmic and two nuclear regions. Both the A1 and A2 mating types were found throughout the state. When both mating types were recovered from the same field, pairings of isolates yielded viable oospores, indicating for the first time the potential for sexual sporulation by P. nicotianae in natural populations. Because the loss of complete resistance required a renewed use of the fungicide mefenoxam, a subset of the survey isolates was screened for sensitivity to the fungicide. All isolates were sensitive, with a mean effective concentration to inhibit 50% of hyphal growth of 0.4 μg/ml that was similar across mating types and races. Molecular characterization of 226 isolates revealed that the pathogen exists as multiple clonal types within the state. Genetic diversity among the pathogen population and the potential for sexual recombination may help explain the ability of the pathogen to rapidly adapt to host resistance genes.
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characterization of Phytophthora nicotianae resistance conferred by the introgressed nicotiana rustica region wz in flue cured tobacco
Plant Disease, 2017Co-Authors: Kestrel Lannon Mccorkle, Ramsey S. Lewis, Katherine E Drakestowe, David H ShewAbstract:Black shank, caused by Phytophthora nicotianae, is one of the most important diseases affecting tobacco worldwide and is primarily managed through use of host resistance. An additional source of re...
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characterization of Phytophthora nicotianae resistance conferred by the introgressed nicotiana rustica region wz in flue cured tobacco
Plant Disease, 2017Co-Authors: Kestrel Mccorkle, Ramsey S. Lewis, Katherine E Drakestowe, David H ShewAbstract:Black shank, caused by Phytophthora nicotianae, is one of the most important diseases affecting tobacco worldwide and is primarily managed through use of host resistance. An additional source of resistance to P. nicotianae, designated as Wz, has been introgressed into Nicotiana tabacum from N. rustica. The Wz gene region confers high levels of resistance to all races, but has not been characterized. Our study found Wz-mediated resistance is most highly expressed in the roots, with only a slight reduction in stem-lesion size in Wz genotypes compared with susceptible controls. No substantial relationships were observed between initial inoculum levels and disease development on Wz genotypes, which is generally consistent with qualitative or complete resistance. Isolates of P. nicotianae adapted for five host generations on plants with the Wz gene caused higher disease severity than isolates adapted on Wz plants for only one host generation. Wz-adapted isolates did not exhibit increased aggressiveness on geno...
Kestrel Lannon Mccorkle - One of the best experts on this subject based on the ideXlab platform.
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adaptation of Phytophthora nicotianae to multiple sources of partial resistance in tobacco
Plant Disease, 2021Co-Authors: Jing Jin, Ramsey S. Lewis, Kestrel Lannon Mccorkle, Vicki Cornish, Ignazio Carbone, David H ShewAbstract:Host resistance is an important tool in the management of black shank disease of tobacco. While race development leads to rapid loss of single-gene resistance, the adaptation by Phytophthora nicotianae to sources of partial resistance from Beinhart 1000, Florida 301, and the Wz gene region introgressed from Nicotiana rustica is poorly characterized. In greenhouse environments, host genotypes with QTLs conferring resistance from multiple sources were initially inoculated with an aggressive isolate of race 0 or race 1 of P. nicotianae. The most aggressive isolate was selected after each of six host generations to inoculate the next generation of plants. The race 0 isolate demonstrated a continuous gradual increase in disease severity and percent root rot on all sources of resistance except the genotype K 326 Wz/--, where a large increase in both was observed between generations two and three. Adaptation by the race 0 isolate on Beinhart 1000 represents the first report of adaptation to this genotype by P. nicotianae. The race 1 isolate did not exhibit significant increases in aggressiveness over generations, but also exhibited a large increase in aggressiveness on K 326 Wz/-- between generations 3 and 4. Molecular characterization of isolates recovered during selection was completed using ddRADseq, but no polymorphisms were associated with the observed changes in aggressiveness. The rapid adaptation to Wz resistance and the gradual adaptation to other QTLs highlights the need to study the nature of Wz resistance and for conducting field studies on efficacy of resistance-gene rotation for disease management.
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characterization of the black shank pathogen Phytophthora nicotianae across north carolina tobacco production areas
Plant Disease, 2017Co-Authors: Courtney Gallup, Kestrel Lannon Mccorkle, Kelly L Ivors, David H ShewAbstract:Black shank disease of tobacco, caused by the oomycete Phytophthora nicotianae, is a major threat to production in the United States and tobacco-producing areas worldwide. In a statewide survey of North Carolina, the rapid shift from race 0 to race 1 was documented. Collected pathogen isolates were characterized phenotypically for mating type and mefenoxam sensitivity, and genotypically by comparing sequences from three cytoplasmic and two nuclear regions. Both the A1 and A2 mating types were found throughout the state. When both mating types were recovered from the same field, pairings of isolates yielded viable oospores, indicating for the first time the potential for sexual sporulation by P. nicotianae in natural populations. Because the loss of complete resistance required a renewed use of the fungicide mefenoxam, a subset of the survey isolates was screened for sensitivity to the fungicide. All isolates were sensitive, with a mean effective concentration to inhibit 50% of hyphal growth of 0.4 μg/ml that was similar across mating types and races. Molecular characterization of 226 isolates revealed that the pathogen exists as multiple clonal types within the state. Genetic diversity among the pathogen population and the potential for sexual recombination may help explain the ability of the pathogen to rapidly adapt to host resistance genes.
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characterization of Phytophthora nicotianae resistance conferred by the introgressed nicotiana rustica region wz in flue cured tobacco
Plant Disease, 2017Co-Authors: Kestrel Lannon Mccorkle, Ramsey S. Lewis, Katherine E Drakestowe, David H ShewAbstract:Black shank, caused by Phytophthora nicotianae, is one of the most important diseases affecting tobacco worldwide and is primarily managed through use of host resistance. An additional source of re...
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resistance to Phytophthora nicotianae in tobacco breeding lines derived from variety beinhart 1000
Plant Disease, 2013Co-Authors: Kestrel Lannon Mccorkle, Ramsey S. Lewis, David ShewAbstract:Abstract Black shank, caused by Phytophthora nicotianae, is managed primarily by host resistance. The rapid emergence of race 1 eliminated the usefulness of available complete resistance, leading breeders to search for new sources of resistance. Cigar tobacco ‘Beinhart 1000’ (BH) is highly resistant to all races of P. nicotianae. Doubled-haploid (DH) lines from a cross of BH and the susceptible ‘Hicks’ were evaluated for black shank resistance, and quantitative trait loci (QTL) on linkage groups (LGs) 4 and 8 accounted for >43% of the phenotypic variation in resistance. Forty-three DH lines and parents were evaluated, and genotypes with one or both QTL from BH on LGs 4 and 8 had increased incubation periods and decreased root rot but higher final inoculum levels than genotypes with neither QTL. A low level of stem resistance was observed in BH and DH lines with the QTL from BH on LG 4 but not LG 8. Low levels of leaf resistance were seen for Hicks, BH, and DH lines with both QTL from BH on LG 4 and 8. The...
Chuanxue Hong - One of the best experts on this subject based on the ideXlab platform.
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population structure mating type and mefenoxam sensitivity of Phytophthora nicotianae in virginia tobacco fields
Plant Disease, 2010Co-Authors: Venkatesan Parkunan, Charles S Johnson, Brian C Bowman, Chuanxue HongAbstract:ABSTRACT Black shank is an important disease of tobacco (Nicotiana tabacum) caused by the fungus-like organism, Phytophthora nicotianae. Three physiological races (0, 1, and 3) have been documented in the United States. Shifts in the pathogen population structure have become a concern due to the widespread use of cultivars possessing resistance to race 0 arising from a single gene (Php or Phl). A comprehensive statewide survey conducted throughout major tobacco-growing areas during summer 2006 and supplemented by additional isolates in 2007 and 2008 yielded 217 isolates from flue-cured, burley, and dark fire-cured tobacco fields. After determining species identity using a single-strand conformational polymorphism fingerprinting technique, the race identity of isolates was assessed via greenhouse tests using three differential cultivars (Hicks, L8, and NC1071). Approximately 76% of the isolates belonged to race 1, 21% to race 0, and the remaining 3% were race 3. This race structure was comparable with thos...
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mefenoxam sensitivity and fitness analysis of Phytophthora nicotianae isolates from nurseries in virginia usa
Plant Pathology, 2008Co-Authors: Chuanxue Hong, Erik L. Stromberg, Gary W. MoormanAbstract:Mefenoxam is one of the most commonly used fungicides for managing diseases caused by Phytophthora spp. on ornamentals. The objectives of this study were to determine whether Phytophthora nicotianae, a destructive pathogen of numerous herbaceous annual and perennial plant species in nurseries, has developed resistance to mefenoxam, and to evaluate the fitness of mefenoxam-resistant isolates. Ninety-five isolates of P. nicotianae were screened for sensitivity to mefenoxam on 20% clarified V8 agar at 100 a.i. µg mL−1. Twenty-five isolates were highly resistant to this compound with EC50 values ranging from 235·2 to 466·3 µg mL−1 and four were intermediately resistant with EC50 values ranging from 1·6 to 2·9 µg mL−1. Sixty-six isolates were sensitive with EC50 values less than 0·04 µg mL−1. Nine resistant and seven sensitive isolates were tested for mefenoxam sensitivity on Pelargonium × hortorum cv. White Orbit. Mefenoxam provided good protection of pelargonium seedlings from colonization by sensitive isolates, but not by any resistant isolates. Four resistant and four sensitive isolates were compared for fitness components and their relative competitive ability on Lupinus Russell Hybrids in the absence of mefenoxam. Resistant isolates outcompeted sensitive ones within 3 to 6 sporulation cycles on lupin seedlings, regardless of their initial proportions in mixed zoospore inoculum. Resistant isolates exhibited greater infection rate and higher sporulation ability than sensitive ones when they were applied separately onto lupins. These results suggest that fungicide resistance may pose a serious challenge to the continued effectiveness of mefenoxam as a control option for nursery growers.
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A simple in-vitro 'wet-plate' method for mass production of Phytophthora nicotianae zoospores and factors influencing zoospore production.
Journal of microbiological methods, 2007Co-Authors: M O Ahonsi, Thomas J Banko, Chuanxue HongAbstract:A simple in-vitro ‘wet-plate’ method for mass-producing Phytophthora nicotianae zoospores at ≥1.0×10 6 zoospores/ml is described. Temperature critically affected zoospore production; 22 °C was optimum, while 36 °C was completely inhibitory. Zoospores being the most important propagule of P. nicotianae, temperature of recycled irrigation water may be manipulated to reduce diseases in irrigated nursery crops. © 2007 Elsevier B.V. All rights reserved.
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effects of propamocarb hydrochloride on mycelial growth sporulation and infection by Phytophthora nicotianae isolates from virginia nurseries
Plant Disease, 2007Co-Authors: Jiahuai Hu, Chuanxue Hong, Erik L. Stromberg, Gary W. MoormanAbstract:ABSTRACT Propamocarb hydrochloride is a systemic fungicide commonly used for control of Phytophthora diseases of nursery crops. Here we report on the effect of this compound on different growth stages of Phytophthora nicotianae, a major pathogen of numerous herbaceous and some woody ornamental plants. A total of 71 isolates were assayed for sensitivity to propamocarb at two concentrations of 1.8 mg/ml (label rate) and 10 mg/ml using clarified V8 agar as a base medium. All isolates grew at 10 mg/ml with the most sensitive isolate having 34.8% relative growth compared with growth on nonamended medium. Nine isolates were selected and further tested for mycelial growth at 0, 1, 10, 25, 50, and 100 mg/ml, and for sporangium production, zoospore motility, and germination at 0, 5, 50, 500, 5,000, and 50,000 μg/ml. EC50 values ranged from 2.2 to 90.1 mg/ml for mycelial growth, 133.8 to 481.3 μg/ml for sporangium production, 88.1 to 249.8 μg/ml for zoospore motility, and 1.9 to 184.6 μg/ml for zoospore germination...
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Effects of propamocarb hydrochloride on mycelial growth, sporulation, and infection by Phytophthora nicotianae isolates from virginia nurseries
Plant disease, 2007Co-Authors: Chuanxue Hong, Erik L. Stromberg, Gary W. MoormanAbstract:Propamocarb hydrochloride is a systemic fungicide commonly used for control of Phytophthora diseases of nursery crops. Here we report on the effect of this compound on different growth stages of Phytophthora nicotianae, a major pathogen of numerous herbaceous and some woody ornamental plants. A total of 71 isolates were assayed for sensitivity to propamocarb at two concentrations of 1.8 mg/ml (label rate) and 10 mg/ml using clarified V8 agar as a base medium. All isolates grew at 10 mg/ml with the most sensitive isolate having 34.8% relative growth compared with growth on nonamended medium. Nine isolates were selected and further tested for mycelial growth at 0, 1, 10, 25, 50, and 100 mg/ml, and for sporangium production, zoospore motility, and germination at 0, 5, 50, 500, 5,000, and 50,000 μg/ml. EC50 values ranged from 2.2 to 90.1 mg/ml for mycelial growth, 133.8 to 481.3 μg/ml for sporangium production, 88.1 to 249.8 μg/ml for zoospore motility, and 1.9 to 184.6 μg/ml for zoospore germination, respectively. In addition, 17 selected isolates were evaluated for propamocarb sensitivity on Pelargonium × hortorum cv. White Orbit. Two days after seedlings were treated with propamocarb at 3.6 mg/ml, they were inoculated by either inverting one 5-mm-diameter plug of a 3-day-old culture or applying a 10-μl drop containing 20 zoospores onto each cotyledon. Propamocarb hydrochloride provided good protection of geranium seedlings from zoospore infections but not from mycelial infections. These results suggest that this fungicide must be used preventively for Phytophthora disease management and that mycelial growth may not be the most reliable measurement to determine the development of fungicide resistance to this compound in Phytophthora species at production facilities and in the landscape.
Katherine E Drakestowe - One of the best experts on this subject based on the ideXlab platform.
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characterization of Phytophthora nicotianae resistance conferred by the introgressed nicotiana rustica region wz in flue cured tobacco
Plant Disease, 2017Co-Authors: Kestrel Lannon Mccorkle, Ramsey S. Lewis, Katherine E Drakestowe, David H ShewAbstract:Black shank, caused by Phytophthora nicotianae, is one of the most important diseases affecting tobacco worldwide and is primarily managed through use of host resistance. An additional source of re...
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characterization of Phytophthora nicotianae resistance conferred by the introgressed nicotiana rustica region wz in flue cured tobacco
Plant Disease, 2017Co-Authors: Kestrel Mccorkle, Ramsey S. Lewis, Katherine E Drakestowe, David H ShewAbstract:Black shank, caused by Phytophthora nicotianae, is one of the most important diseases affecting tobacco worldwide and is primarily managed through use of host resistance. An additional source of resistance to P. nicotianae, designated as Wz, has been introgressed into Nicotiana tabacum from N. rustica. The Wz gene region confers high levels of resistance to all races, but has not been characterized. Our study found Wz-mediated resistance is most highly expressed in the roots, with only a slight reduction in stem-lesion size in Wz genotypes compared with susceptible controls. No substantial relationships were observed between initial inoculum levels and disease development on Wz genotypes, which is generally consistent with qualitative or complete resistance. Isolates of P. nicotianae adapted for five host generations on plants with the Wz gene caused higher disease severity than isolates adapted on Wz plants for only one host generation. Wz-adapted isolates did not exhibit increased aggressiveness on geno...
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the tobacco trichome exudate z abienol and its relationship with plant resistance to Phytophthora nicotianae
Plant Disease, 2017Co-Authors: William T Steede, Katherine E Drakestowe, David H Shew, Sheri P Kernodle, Justin M, David P Eickholt, David A Danehower, Ramsey S. LewisAbstract:In previous research, we discovered a favorable quantitative trait locus (QTL) in cigar tobacco cultivar 'Beinhart 1000' designated as Phn15.1, which provides a high level of partial resistance to the black shank disease caused by Phytophthora nicotianae. A very close genetic association was also found between Phn15.1 and the ability to biosynthesize Z-abienol, a labdanoid diterpene exuded by the trichomes onto above-ground plant parts, and that imparts flavor and aroma characteristics to Oriental and some cigar tobacco types. Because accumulation of Z-abienol is considered to be undesirable for cultivars of other tobacco types, we herein describe a series of experiments to gain insight on whether this close association is due to genetic linkage or pleiotropy. First, in an in vitro bioassay, we observed Z-abienol and related diterpenes to inhibit hyphal growth of P. nicotianae at concentrations between 0.01 and 100 ppm. Secondly, we field-tested transgenic versions of Beinhart 1000 carrying RNAi constructs for downregulating NtCPS2 or NtABS, two genes involved in the biosynthesis of Z-abienol. Thirdly, we also field tested a recombinant inbred line population segregating for a truncation mutation in NtCPS2 leading to an interrupted Z-abienol pathway. We observed no correlation between field resistance to P. nicotianae and the ability to accumulate Z-abienol in either the transgenic materials or the mapping population. Results suggest that, although Z-abienol may affect P. nicotianae when applied at high concentrations in in vitro assays, the compound has little effect on black shank disease development under natural field conditions. Thus, it should be possible to disassociate Phn15.1-mediated black shank resistance identified in cigar tobacco cultivar Beinhart 1000 from the ability to accumulate Z-abienol, an undesirable secondary metabolite for burley and flue-cured tobacco cultivars.