scholarly journals Managing the Race Structure of Phytophthora parasitica var. nicotianae with Cultivar Rotation

Plant Disease ◽  
2005 ◽  
Vol 89 (12) ◽  
pp. 1285-1294 ◽  
Author(s):  
M. J. Sullivan ◽  
T. A. Melton ◽  
H. D. Shew
Keyword(s):  
Partial Resistance ◽  
Disease Incidence ◽  
Single Gene ◽  
Growing Season ◽  
Phytophthora Parasitica ◽  
Black Shank ◽  
Complete Resistance ◽  
Race 1 ◽  
High Level ◽  
Different Levels

Deployment of tobacco cultivars with single-gene, complete resistance to race 0 of the tobacco black shank pathogen, Phytophthora parasitica var. nicotianae, has resulted in a rapid increase in the occurrence of race 1 of the pathogen in North Carolina. Cultivar-rotation studies were conducted in three fields to assess how different levels and types of resistance affected the race structure and population dynamics of the pathogen when deployed in fields initially containing single or mixed races of the pathogen. In a field with both races present, a high level of partial resistance in cv. K 346 was most effective in reducing disease and decreasing the proportion of race 1 in the pathogen population. The deployment of complete resistance in cv. NC 71 resulted in intermediate levels of disease control and race 1 became the predominate race. The cv. K 326, with a low level of partial resistance, had the highest levels of disease, and race 0 was the dominant race recovered. In a field where no race 1 was detected initially, disease incidence was high with the use of partial resistance. Complete resistance was very effective in suppressing disease, but race 1 was recovered after only one growing season. By the end of the third growing season, race 1 was recovered from most treatments where single-gene resistance was deployed. A high level of partial resistance was most effective in suppressing disease in a field where race 1 initially was the predominant race. A rotation between cultivars with single-gene resistance and cultivars with a high level of partial resistance should provide the most effective approach to black shank management. This rotation will reduce disease incidence and minimize race shifts in the pathogen and, over time, should prolong the usefulness of the Ph gene for black shank control in commercial production of tobacco.

Adaptation of Phytophthora nicotianae to multiple sources of partial-resistance in tobacco.

Plant Disease ◽  
2021 ◽  
Author(s):  
Jing Jin ◽  
Kestrel Lannon McCorkle ◽  
Vicki Cornish ◽  
Ignazio Carbone ◽  
Ramsey Lewis ◽  
...  
Keyword(s):  
Partial Resistance ◽  
Single Gene ◽  
Field Studies ◽  
Phytophthora Nicotianae ◽  
Multiple Sources ◽  
Rapid Loss ◽  
Sources Of Resistance ◽  
Black Shank ◽  
Race 1

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.

scholarly journals Selection for Resistance to Verticillium Wilt Caused by Race 2 Isolates of Verticillium dahliae in Accessions of Lettuce (Lactuca sativa L.)

HortScience ◽  
2011 ◽  
Vol 46 (2) ◽  
pp. 201-206 ◽  
Author(s):  
Ryan J. Hayes ◽  
Karunakaran Maruthachalam ◽  
Gary E. Vallad ◽  
Steven J. Klosterman ◽  
Krishna V. Subbarao
Keyword(s):  
Genetic Variation ◽  
Verticillium Wilt ◽  
Verticillium Dahliae ◽  
Partial Resistance ◽  
Disease Incidence ◽  
Greenhouse Experiments ◽  
Complete Resistance ◽  
Race 1 ◽  
Selection For ◽  
Race 2

Verticillium wilt of lettuce caused by Verticillium dahliae can cause severe economic damage to lettuce producers. The pathogen exists as two races (Races 1 and 2) in lettuce, and complete resistance to Race 1 is known. Resistance to Race 2 isolates has not been reported, and production of Race 1-resistant cultivars will likely increase the frequency of Race 2 strains. The objective of this research was to select lettuce accessions for resistance to Race 2 isolates of V. dahliae. Two independent populations totaling 314 randomly sampled PIs were evaluated for Verticillium wilt disease incidence (DI) caused by V. dahliae isolate VdLs17 in one unreplicated and two replicated greenhouse experiments. Selection for PIs with reduced DI was conducted between each experiment and plant stems were plated on semiselective media to identify colonized plants that remained non-symptomatic. No accession with complete resistance was identified, although accessions with partial resistance were selected. Genetic variation for the frequency of V. dahliae-colonized plants that remain symptomless was detected. Four PIs (169511, 171674, 204707, and 226641) were selected for further testing in three replicated greenhouse experiments and demonstrated significantly lower disease incidence than the susceptible control cultivars. The results indicate that lettuce has genetic variation for partial resistance to a Race 2 isolate of V. dahliae. The resistant PIs selected in this research are morphologically diverse, and no dependence between rate of bolting and resistance was found. PIs with partial resistance may be useful for breeding lettuce cultivars with resistance to Race 2 isolates of V. dahliae.

Components of aggressiveness in Phytophthora nicotianae during adaptation to multiple sources of partial resistance in tobacco

Plant Disease ◽  
2020 ◽  
Author(s):  
Jing Jin ◽  
H. David Shew
Keyword(s):  
Partial Resistance ◽  
Single Gene ◽  
Phytophthora Nicotianae ◽  
Root Tip ◽  
Multiple Sources ◽  
Root Tips ◽  
Black Shank ◽  
Resistance Sources ◽  
Infected Root ◽  
Race 1

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 gene from Nicotiana rustica. An aggressive isolate of the two major races of P. nicotianae, race 0 and race 1, were 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 root tips, produced more sporangia per infected root tip, and caused larger lesions than their respective non-adapted isolates of the same race and from the same resistance source. Adapted isolates also produced more aggressive zoospore progeny than the non-adapted isolates. Adaptation to partial resistance involves multiple aggressiveness components that 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.

scholarly journals Resistance to Phytophthora nicotianae in Tobacco Breeding Lines Derived from Variety Beinhart 1000

Plant Disease ◽  
2013 ◽  
Vol 97 (2) ◽  
pp. 252-258 ◽  
Author(s):  
Kestrel McCorkle ◽  
Ramsey Lewis ◽  
David Shew
Keyword(s):  
Partial Resistance ◽  
Phytophthora Nicotianae ◽  
Sources Of Resistance ◽  
Black Shank ◽  
Breeding Lines ◽  
Stem Resistance ◽  
Race 1 ◽  
Low Levels ◽  
Dh Lines ◽  
Rapid Emergence

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 partial resistance from BH has not been used commercially and may provide an increase in level of partial resistance in future tobacco varieties.

scholarly journals Effects of Chemical Control, Cultivar Resistance, and Structure of Cultivar Root System on Black Shank Incidence of Tobacco

Plant Disease ◽  
2010 ◽  
Vol 94 (5) ◽  
pp. 613-620 ◽  
Author(s):  
Dimitrios F. Antonopoulos ◽  
Thomas Melton ◽  
Asimina L. Mila
Keyword(s):  
Partial Resistance ◽  
Adventitious Roots ◽  
Early Stage ◽  
Laboratory Studies ◽  
Critical Factors ◽  
Cultivar Resistance ◽  
Black Shank ◽  
Initial Application ◽  
Race 1 ◽  
Tobacco Growth

Black shank, caused by the hemibiotrophic oomycete Phytophthora parasitica var. nicotianae, is a major disease of tobacco (Nicotiana tabacum). The rise of race 1 in the late 1990s, after extensive cropping of cultivars possessing the Php gene, confirming immunity to race 0 of P. parasitica var. nicotianae, imposed new challenges to black shank management. The effects of tobacco cultivars and chemical controls with mefenoxam (Ridomil Gold) on black shank incidence were investigated in naturally infested fields. Twenty-five cultivars were tested and the highest resistance for races 0 and 1 of P. parasitica var. nicotianae was provided by RJR 75 and SP 227 based on field and laboratory studies. When race 1 was prevalent, mefenoxam was effective to control black shank. An initial application at an early stage of tobacco growth, such as a few days before or after transplant, was essential to successfully control the disease. In greenhouse experiments, cultivars carrying the Php gene produced fewer and shorter adventitious roots than cultivars possessing only partial resistance to all races of P. parasitica var. nicotianae. Strategies such as use of mefenoxam, especially at an early stage, when adventitious roots are emerging, and planting a cultivar with high partial resistance or possessing the Ph gene when race 1 or race 0, respectively, predominates are critical factors in reducing loss due to P. parasitica var. nicotianae.

scholarly journals Fitness of Races 0 and 1 of Phytophthora parasitica var. nicotianae

Plant Disease ◽  
2005 ◽  
Vol 89 (11) ◽  
pp. 1220-1228 ◽  
Author(s):  
M. J. Sullivan ◽  
T. A. Melton ◽  
H. D. Shew
Keyword(s):  
Partial Resistance ◽  
Minor Effect ◽  
Population Declines ◽  
Phytophthora Parasitica ◽  
Growing Seasons ◽  
Incubation Periods ◽  
Race 1 ◽  
Study Population ◽  
Overwintering Survival ◽  
Pathogen Populations

Deployment of tobacco (Nicotiana tabacum) varieties with complete resistance to race 0 of Phytophthora parasitica var. nicotianae has led to a rapid increase in the field populations of race 1 in North Carolina. In a field study, population levels of race 1 decreased relative to race 0 when cultivars with partial resistance to both races were planted, suggesting that race 1 isolates were less fit than race 0 isolates. Experiments were conducted to quantify differences in aggressiveness and survivability of the two races. Tobacco varieties with low, moderate, or high levels of partial resistance were inoculated with 60 pathogen isolates, and symptom development was monitored for 3 weeks. Race 0 isolates were more aggressive than race 1 isolates on cultivars with moderate or high levels of partial resistance; incubation periods were shorter and root rot severity was greater with race 0 isolates. Isolates of race 1, however, caused greater stunting of plants with moderate and high levels of partial resistance than race 0 isolates. Field microplots were infested with either a single race or an equal mixture of each race. Soil samples were collected at the end of two growing seasons and again the following spring. Pathogen populations declined from 40 to 80% during winter months, but population declines for race 0 were lower than for race 1 in each treatment over each winter. Race shifts from race 1 to race 0 that were observed in the presence of cultivars with partial resistance appear to be primarily the result of differences in aggressiveness of the races, with a possible minor effect of enhanced overwintering survival of race 0 compared with race 1.

scholarly journals Avena sterilis L. Genotypes as a Potential Source of Resistance to Oat Powdery Mildew

Plant Disease ◽  
2016 ◽  
Vol 100 (10) ◽  
pp. 2145-2151 ◽  
Author(s):  
Sylwia Okoń ◽  
Edyta Paczos-Grzęda ◽  
Tomasz Ociepa ◽  
Aneta Koroluk ◽  
Sylwia Sowa ◽  
...  
Keyword(s):  
Powdery Mildew ◽  
Single Gene ◽  
Screening Tests ◽  
Single Spore ◽  
Avena Sterilis ◽  
Breeding Programs ◽  
Host Pathogen ◽  
Pathogen Screening ◽  
High Level ◽  
Different Levels

The aim of the present study was to identify Avena sterilis genotypes demonstrating a high level of resistance against oat powdery mildew, using host-pathogen tests. The study was conducted on 350 A. sterilis genotypes from different parts of the world. Six single-spore isolates of Blumeria graminis (DC.) f. sp. avenae, which demonstrated different levels of virulence to control lines and cultivars, were used in host-pathogen screening tests. To confirm the resistant response of selected genotypes, 13 other isolates were used. Reactions to the isolates were grouped into three classes: resistant, intermediate, and susceptible. Susceptible cultivars Sam and Fuchs were used as controls to estimate the degree of infection. The results of the screening test showed that 10 genotypes were classified as resistant. The second test based on 13 other isolates revealed that only four of the 10 genotypes were a valuable source of resistance against powdery mildew. The identified genotypes may be used in oat breeding programs to increase the level of resistance against powdery mildew. First, however, further studies aimed at identifying whether this resistance is conditioned by a single gene or combinations of different genes are required.

scholarly journals Importance of the Secondary Genepool in Barley Genetics and Breeding II. Disease Resistance, Agronomic Performance and Quality

2011 ◽  
Vol 40 (No. 3) ◽  
pp. 79-85 ◽  
Author(s):  
R. Pickering ◽  
E. Niks R ◽  
A. Johnston P ◽  
C. Butler R
Keyword(s):  
Disease Resistance ◽  
Leaf Rust ◽  
Partial Resistance ◽  
Disease Development ◽  
Agronomic Performance ◽  
Yield And Quality ◽  
Complete Resistance ◽  
High Level ◽  
Yield Trials ◽  
Breeding Techniques

In this second paper on the use of secondary genepools in barley improvement, we describe the characterisation of leaf rust resistant recombinant lines (RLs) derived from Hordeum vulgare × H. bulbosum crosses. Twelve RLs were inoculated with leaf rust and the early stages of disease development were observed. Several RLs showed complete resistance to the pathogen, but others had a high level of partial resistance, which may be durable. Some of these RLs and others were tested in yield trials to determine the effects of introgressed chromatin from H. bulbosum on yield and quality. We conclude that there are no major adverse effects that cannot be overcome through normal breeding techniques.  

scholarly journals An Assessment of the Genetic Diversity in a Field Population of Phytophthora nicotianae with a Changing Race Structure

Plant Disease ◽  
2010 ◽  
Vol 94 (4) ◽  
pp. 455-460 ◽  
Author(s):  
M. J. Sullivan ◽  
E. J. Parks ◽  
M. A. Cubeta ◽  
C. A. Gallup ◽  
T. A. Melton ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Single Gene ◽  
Phytophthora Nicotianae ◽  
Bootstrap Support ◽  
Resistant Variety ◽  
Aflp Analysis ◽  
Pathogen Population ◽  
Independent Events ◽  
Race 1 ◽  
High Level

One hundred fifty-three isolates of Phytophthora nicotianae that were collected over a 4-year period from a single field were subjected to amplified fragment length polymorphism (AFLP) analysis to investigate the effect of different types of resistance in tobacco (Nicotiana tabacum) on genetic diversity in the pathogen population. No race 1 isolates were detected in the field prior to initiating the study, but the race was present in multiple plots by the end of the 4-year period. There were 102 race 0 isolates and 51 race 1 isolates characterized. Seventy-six of the 153 isolates had a unique AFLP profile, whereas the remaining 77 isolates were represented by 27 AFLP profiles shared by at least two isolates. Isolates of both races were found in both the unique and shared AFLP profile groups. Twenty-three of the AFLP profiles were detected in multiple years, indicating a clonal component to the pathogen population. Race 1 isolates that were detected over multiple years were always obtained from the same plot. No race 1 profile was found in more than one plot, confirming the hypothesis that the multiple occurrences of the race throughout the field were the result of independent events and not pathogen spread. Three identical race 0 AFLP profiles occurred in noncontiguous plots, and in each case, the plots contained the same partially resistant variety. Cluster analysis provided a high level of bootstrap support for 41 isolates in 19 clusters that grouped primarily by race and rotation treatment. Estimates of genetic diversity ranged from 0.365 to 0.831 and varied depending on tobacco cultivar planted and race. When averaged over all treatments, diversity in race 1 isolates was lower than in race 0 isolates at the end of each season. Deployment of single-gene resistance initially decreased genetic diversity of the population, but the diversity increased each year, indicating the pathogen was adapting to the host genotypes deployed in the field.

scholarly journals Relationship of Isolate Origin to Pathogenicity of Race 0 and 1 of Phytophthora parasitica var. nicotianae on Tobacco Cultivars

Plant Disease ◽  
2005 ◽  
Vol 89 (3) ◽  
pp. 332-337 ◽  
Author(s):  
A. S. Csinos
Keyword(s):  
Breeding Line ◽  
Phytophthora Parasitica ◽  
Black Shank ◽  
Inoculation Technique ◽  
Race 1 ◽  
Relationship Of ◽  
Similar Evaluation ◽  
Made In ◽  
Tobacco Black Shank ◽  
Tobacco Belt

Flue-cured tobacco cultivars were evaluated for their reaction to race 0 and race 1 of Phytophthora parasitica var. nicotianae, the incitant of the disease tobacco black shank. Seventeen commercial tobacco cultivars having resistance derived from Fla 301 or a combination of Fla 301 and Fla 105 were subjected to root or stem inoculation by 22 different isolates of P. parasitic var. nicotianae collected from across the Georgia tobacco-growing belt. An adapted stem inoculation technique using field-grown tobacco indicator cvs. K-326, NC-71, Coker 371 Gold, and the breeding line NC-1071 was used to determine races of P. parasitica var. nicotianae. Typically, in greenhouse evaluations, cultivars stem inoculated with race 1 of P. parasitica var. nicotianae were killed. Cultivars that had resistance from both Fla 301 and Fla 105 (Ph gene) were not killed, with few exceptions, when inoculated with race 0. Fifty-seven tobacco specimens having black shank symptoms from the Georgia and Florida tobacco belt were evaluated for P. parasitica var. nicotianae race using the adapted stem inoculation technique. Of the samples evaluated from commercial tobacco fields, 83% yielded race 1 compared with a similar evaluation made in 1994, where only 16% of the samples yielded race 1. The increase in race 1 incidence may be related to the increase in use of cultivars which have the Ph gene for resistance. The use of rotations and metalaxyl or mefenoxam may be required where race 1 is found.

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