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Article: Impacts of Continued Exposure to a Susceptible Host Genotype on Aggressiveness of

Jin, Jing / Shew, H David

2022 Volume 106, Issue 2, Page(s) 373–381

Abstract: Pathogen adaptation can threaten the durability of partial resistance. Mixed plantings of susceptible and partially resistant varieties may prolong the effectiveness of partial resistance, but little is known about how continued exposure to a susceptible ...

Abstract	Pathogen adaptation can threaten the durability of partial resistance. Mixed plantings of susceptible and partially resistant varieties may prolong the effectiveness of partial resistance, but little is known about how continued exposure to a susceptible genotype can change the aggressiveness of pathogen isolates adapted to a source of partial resistance. The objective of this study was to examine the effects of continued exposure to a highly susceptible tobacco genotype on isolates of
MeSH term(s)	Genotype ; Phytophthora/genetics ; Nicotiana/genetics ; Virulence
Language	English
Publishing date	2022-02-09
Publishing country	United States
Document type	Journal Article
ZDB-ID	754182-x
ISSN	0191-2917
ISSN	0191-2917
DOI	10.1094/PDIS-09-20-1972-RE
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Article: Impacts of Continued Exposure to a Susceptible Host Genotype on Aggressiveness of Phytophthora nicotianae Isolates Adapted to Multiple Sources of Partial Resistance

Jin, Jing / Shew, H. David

Plant disease. 2022 Feb. 28, v. 106, no. 2

2022

Abstract	Pathogen adaptation can threaten the durability of partial resistance. Mixed plantings of susceptible and partially resistant varieties may prolong the effectiveness of partial resistance, but little is known about how continued exposure to a susceptible genotype can change the aggressiveness of pathogen isolates adapted to a source of partial resistance. The objective of this study was to examine the effects of continued exposure to a highly susceptible tobacco genotype on isolates of Phytophthora nicotianae that had been adapted to partial resistance. Isolates of P. nicotianae previously adapted to two sources of partial resistance were continually exposed to either the original host of adaptation or a susceptible host. After six generations of host exposure, isolates obtained from the partially resistant and the susceptible hosts were compared for their aggressiveness on the resistant host and for differences in expression of genes associated with pathogenicity and aggressiveness. Results suggested that exposure to the susceptible tobacco genotype reduced aggressiveness of isolates adapted to partial resistance in K 326 Wz/– but not of isolates adapted to partial resistance in Fla 301. Quantification of pathogenicity-associated gene expression using qRT-PCR suggested the rapid change in aggressiveness of isolates adapted to Wz-sourced partial resistance may have resulted from modification in gene expression in multiple genes.
Keywords	Phytophthora nicotianae ; durability ; gene expression ; genotype ; pathogenicity ; pathogens ; tobacco
Language	English
Dates of publication	2022-0228
Size	p. 373-381.
Publishing place	The American Phytopathological Society
Document type	Article
ZDB-ID	754182-x
ISSN	0191-2917
ISSN	0191-2917
DOI	10.1094/PDIS-09-20-1972-RE
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Article: Components of Aggressiveness in

Jin, Jing / Shew, H David

Plant disease

2021 Volume 105, Issue 7, Page(s) 1960–1966

Abstract: Black shank is a devastating disease of tobacco caused ... ...

Abstract	Black shank is a devastating disease of tobacco caused by
MeSH term(s)	Phytophthora/genetics ; Plant Diseases ; Nicotiana
Language	English
Publishing date	2021-08-04
Publishing country	United States
Document type	Journal Article
ZDB-ID	754182-x
ISSN	0191-2917
ISSN	0191-2917
DOI	10.1094/PDIS-09-20-1929-RE
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Article: Components of Aggressiveness in Phytophthora nicotianae During Adaptation to Multiple Sources of Partial Resistance in Tobacco

Jin, Jing / Shew, H. David

Plant disease. 2021 July 19, v. 105, no. 7

2021

Abstract: 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, ... ...

Abstract	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.
Keywords	Nicotiana rustica ; Phytophthora nicotianae ; durability ; genomics ; pathogens ; progeny ; root tips ; sporangia ; tobacco ; zoospores
Language	English
Dates of publication	2021-0719
Size	p. 1960-1966.
Publishing place	The American Phytopathological Society
Document type	Article
ZDB-ID	754182-x
ISSN	0191-2917
ISSN	0191-2917
DOI	10.1094/PDIS-09-20-1929-RE
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Article ; Online: Seasonal dynamics and fungicide sensitivity of organisms causing brown patch of tall fescue in North Carolina.

Koehler, Alyssa M / Shew, H David

Mycologia

2017 Volume 109, Issue 4, Page(s) 667–675

Abstract: Brown patch, caused by multiple species of Rhizoctonia and Rhizoctonia-like fungi, is the most severe summer disease of tall fescue in home lawns across the southeastern United States. Home lawns were surveyed in central North Carolina from 2013 to 2015 ... ...

Abstract	Brown patch, caused by multiple species of Rhizoctonia and Rhizoctonia-like fungi, is the most severe summer disease of tall fescue in home lawns across the southeastern United States. Home lawns were surveyed in central North Carolina from 2013 to 2015 to determine the organisms present during typical epidemics of brown patch in tall fescue. Isolates of Rhizoctonia and Rhizoctonia-like fungi were obtained by sampling 147 locations in July 2013 and May and July 2014. In addition, 11 sites were sampled once a week for 12 consecutive weeks from late May to the end of July 2015. All isolates were identified to species and anastomosis group with nuc rDNA internal transcribed spacer (ITS) sequence analysis. Isolations from brown patch lesions in May 2014 predominately yielded Ceratobasidium cereale (77% of the organisms recovered), whereas the organisms recovered in July 2013 and 2014 were R. solani AG 2-2-IIIB (44%), R. solani AG 1-IB (37%), and R. zeae (14%). In 2015, Ceratobasidium cereale was isolated from all 11 locations in May but was replaced by Rhizoctonia species in June and July. Sensitivity of the May 2014 isolates to multiple concentrations of the fungicides azoxystrobin, flutolanil, fluxapyroxad, and propiconazole was compared with sensitivity of isolates collected in 2003, to determine whether multiple years of exposure to fungicides applied for brown patch control had altered fungicide sensitivity. Historical isolates of R. solani, which had never been exposed to fungicide applications for brown patch control, were also included for comparison. Mean EC
MeSH term(s)	Basidiomycota/classification ; Basidiomycota/drug effects ; Basidiomycota/isolation & purification ; DNA, Fungal/genetics ; DNA, Ribosomal Spacer/genetics ; Festuca/microbiology ; Fungicides, Industrial/pharmacology ; Microbial Sensitivity Tests ; North Carolina ; Plant Diseases/microbiology ; Rhizoctonia/classification ; Rhizoctonia/drug effects ; Rhizoctonia/genetics ; Rhizoctonia/isolation & purification ; Seasons
Chemical Substances	DNA, Fungal ; DNA, Ribosomal Spacer ; Fungicides, Industrial
Language	English
Publishing date	2017-10-11
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	281335-x
ISSN	1557-2536 ; 0027-5514
ISSN (online)	1557-2536
ISSN	0027-5514
DOI	10.1080/00275514.2017.1377587
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Article: Validation of Standard Area Diagrams to Estimate the Severity of Septoria Leaf Spot on Stevia in Paraguay, Mexico, and the United States.

Sanabria-Velazquez, Andres D / Enciso-Maldonado, Guillermo A / Maidana-Ojeda, Marco / Diaz-Najera, Jose F / Thiessen, Lindsey D / Shew, H David

Plant disease

2023 Volume 107, Issue 6, Page(s) 1829–1838

Abstract: Septoria leaf spot (SLS) affects stevia leaves, reducing their quality. Estimates of SLS severity on different genotypes are made to identify resistance and as a basis to compare management approaches. The use of standard area diagrams (SADs) can improve ...

Abstract	Septoria leaf spot (SLS) affects stevia leaves, reducing their quality. Estimates of SLS severity on different genotypes are made to identify resistance and as a basis to compare management approaches. The use of standard area diagrams (SADs) can improve the accuracy and reliability of severity estimates. In this study, we developed new SADs with six illustrations (0.5, 1, 10, 25, 40, and 75% severity). The SADs were validated by raters with and without experience in estimating SLS. Raters evaluated 40 leaf photos with SLS severities ranging from 0 to 100% without and with the SADs. Agreement (ρ
MeSH term(s)	United States ; Stevia ; Mexico ; Reproducibility of Results ; Paraguay ; Ascomycota/genetics
Language	English
Publishing date	2023-06-13
Publishing country	United States
Document type	Journal Article
ZDB-ID	754182-x
ISSN	0191-2917
ISSN	0191-2917
DOI	10.1094/PDIS-07-22-1609-RE
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article: Adaptation of Phytophthora nicotianae to Multiple Sources of Partial Resistance in Tobacco

Jin, Jing / McCorkle, Kestrel L. / Cornish, Vicki / Carbone, Ignazio / Lewis, Ramsey S. / Shew, H. David

Plant disease. 2022 Mar. 28, v. 106, no. 3

2022

Abstract: Host resistance is an important tool in the management of black shank disease of tobacco. Race development leads to rapid loss of single-gene resistance, but the adaptation by Phytophthora nicotianae to sources of partial resistance from Beinhart 1000, ... ...

Abstract	Host resistance is an important tool in the management of black shank disease of tobacco. Race development leads to rapid loss of single-gene resistance, but 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 quantitative trait loci (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 percentage root rot on all sources of resistance except the genotype K 326 Wz/–, where a large increase in both was observed between generations 2 and 3. 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 exhibited a large increase in aggressiveness on K 326 Wz/– between generations 3 and 4. Molecular characterization of isolates recovered during selection was completed via double digest restriction-site associated DNA sequencing, 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 to conduct field studies on the efficacy of resistance gene rotation for disease management.
Keywords	DNA ; Nicotiana rustica ; Phytophthora nicotianae ; black shank disease ; disease control ; disease severity ; genotype ; greenhouses ; quantitative traits ; resistance genes ; root rot ; tobacco
Language	English
Dates of publication	2022-0328
Size	p. 906-917.
Publishing place	The American Phytopathological Society
Document type	Article
ZDB-ID	754182-x
ISSN	0191-2917
ISSN	0191-2917
DOI	10.1094/PDIS-06-21-1241-RE
Database	NAL-Catalogue (AGRICOLA)

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Article ; Online: Validation of Standard Area Diagrams to Estimate the Severity of Septoria Leaf Spot on Stevia in Paraguay, Mexico, and the United States

Sanabria-Velazquez, Andres D. / Enciso-Maldonado, Guillermo A. / Maidana-Ojeda, Marco / Diaz-Najera, Jose F. / Thiessen, Lindsey D. / Shew, H. David

Plant Disease. 2023 June 01, v. 107, no. 6 p.1829-1838

2023

Abstract	Septoria leaf spot (SLS) affects stevia leaves, reducing their quality. Estimates of SLS severity on different genotypes are made to identify resistance and as a basis to compare management approaches. The use of standard area diagrams (SADs) can improve the accuracy and reliability of severity estimates. In this study, we developed new SADs with six illustrations (0.5, 1, 10, 25, 40, and 75% severity). The SADs were validated by raters with and without experience in estimating SLS. Raters evaluated 40 leaf photos with SLS severities ranging from 0 to 100% without and with the SADs. Agreement (ρc), bias (Cb), precision (r), and intracluster correlation (ρ) coefficients were significantly closer to “true” severity values when the SADs was used by inexperienced (ρc = 0.89; Cb = 0.97; r = 0.90, ρ = 0.81) and experienced (ρc = 0.94; Cb = 0.99; r = 0.95, ρ = 0.91) raters. The SADs were tested under field conditions in Paraguay, Mexico, and the United States, with inexperienced raters assigned to two groups, one SADs trained and the other not trained, that estimated SLS severity three times: first, all raters without SADs and no time limit for the estimates; second, only the SADs-trained group used SADs and no time limit; and third, only the SADs-trained group used SADs, with a time limit of 10 s imposed per specimen assessment. Agreement and reliability of SLS severity estimates significantly improved when raters used the SADs without a time limit. The use of the new SADs improved the accuracy, precision, and reliability of SLS severity estimates, enhancing the uniformity in assessment across different stevia programs.
Keywords	Septoria ; Stevia ; leaf spot ; leaves ; Mexico ; Paraguay ; disease severity ; phytopathometry ; Septoria steviae ; Stevia rebaudiana
Language	English
Dates of publication	2023-0601
Size	p. 1829-1838.
Publishing place	The American Phytopathological Society
Document type	Article ; Online
ZDB-ID	754182-x
ISSN	0191-2917
ISSN	0191-2917
DOI	10.1094/PDIS-07-22-1609-RE
Database	NAL-Catalogue (AGRICOLA)

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Article: Adaptation of

Jin, Jing / McCorkle, Kestrel L / Cornish, Vicki / Carbone, Ignazio / Lewis, Ramsey S / Shew, H David

Plant disease

2022 Volume 106, Issue 3, Page(s) 906–917

Abstract: Host resistance is an important tool in the management of black shank disease of tobacco. Race development leads to rapid loss of single-gene resistance, but the adaptation ... ...

Abstract	Host resistance is an important tool in the management of black shank disease of tobacco. Race development leads to rapid loss of single-gene resistance, but the adaptation by
MeSH term(s)	Genotype ; Phytophthora/genetics ; Plant Diseases/genetics ; Quantitative Trait Loci/genetics ; Nicotiana/genetics
Language	English
Publishing date	2022-03-10
Publishing country	United States
Document type	Journal Article
ZDB-ID	754182-x
ISSN	0191-2917
ISSN	0191-2917
DOI	10.1094/PDIS-06-21-1241-RE
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article: Seasonal dynamics and fungicide sensitivity of organisms causing brown patch of tall fescue in North Carolina

Koehler, Alyssa M / Shew, H. David

Mycologia. 2017 July 4, v. 109, no. 4

2017

Abstract	Brown patch, caused by multiple species of Rhizoctonia and Rhizoctonia-like fungi, is the most severe summer disease of tall fescue in home lawns across the southeastern United States. Home lawns were surveyed in central North Carolina from 2013 to 2015 to determine the organisms present during typical epidemics of brown patch in tall fescue. Isolates of Rhizoctonia and Rhizoctonia-like fungi were obtained by sampling 147 locations in July 2013 and May and July 2014. In addition, 11 sites were sampled once a week for 12 consecutive weeks from late May to the end of July 2015. All isolates were identified to species and anastomosis group with nuc rDNA internal transcribed spacer (ITS) sequence analysis. Isolations from brown patch lesions in May 2014 predominately yielded Ceratobasidium cereale (77% of the organisms recovered), whereas the organisms recovered in July 2013 and 2014 were R. solani AG 2-2-IIIB (44%), R. solani AG 1-IB (37%), and R. zeae (14%). In 2015, Ceratobasidium cereale was isolated from all 11 locations in May but was replaced by Rhizoctonia species in June and July. Sensitivity of the May 2014 isolates to multiple concentrations of the fungicides azoxystrobin, flutolanil, fluxapyroxad, and propiconazole was compared with sensitivity of isolates collected in 2003, to determine whether multiple years of exposure to fungicides applied for brown patch control had altered fungicide sensitivity. Historical isolates of R. solani, which had never been exposed to fungicide applications for brown patch control, were also included for comparison. Mean EC₅₀ values (concentration of fungicide needed to inhibit mycelial growth by 50%) varied across fungicides and species, but no resistance was observed, and there was no apparent shift in sensitivity over the years. An additional 94 isolates from 2015 were screened against azoxystrobin, flutolanil, fluxapyroxad, and propiconazole, and fungicide insensitivity was not observed.
Keywords	Ceratobasidium ; Festuca arundinacea ; Rhizoctonia ; azoxystrobin ; flutolanil ; internal transcribed spacers ; mycelium ; propiconazole ; sequence analysis ; summer ; North Carolina
Language	English
Dates of publication	2017-0704
Size	p. 667-675.
Publishing place	Taylor & Francis
Document type	Article
Note	NAL-AP-2-clean
ZDB-ID	281335-x
ISSN	1557-2536 ; 0027-5514
ISSN (online)	1557-2536
ISSN	0027-5514
DOI	10.1080/00275514.2017.1377587
Database	NAL-Catalogue (AGRICOLA)

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