Phytophthora infestans Populations from Tomato and Potato in North Carolina Differ in Genetic Diversity and Structure

Phytophthora infestans causes a destructive disease on tomato and potato. In North Carolina (NC) potatoes are mostly grown in the east, whereas tomatoes are grown in the mountainous areas in the western part of the state. Five genotypes of P. infestans were identified from 93 and 157 isolates collected from tomato and potato over a 5 year period between 1993 and 1998. All isolates collected from potato in eastern NC were the US-8 genotype, whereas only a single isolate was the US-1 genotype. Tuber blight was found on immature daughter tubers in a single field in 1997, however infection on mature tubers was not observed. Within potato fields, a range of sensitivity to metalaxyl was observed among isolates but all were either intermediate or highly resistant to the fungicide. In contrast, isolates from tomatoes included previously reported US-7 and US-8 genotypes and two new genotypes called US-18 and US-19 (A2 mating type, allozyme genotype Gpi 100/100 and Pep 92/100). These genotypes had unique restriction fragment length polymorphism banding patterns, were sensitive to metalaxyl, and have not been reported elsewhere. All genotypes, with the exception of the US-1, were the Ia mitochondrial haplotype. Thus, isolates of P. infestans from tomato were more genetically diverse over time in NC than those from potato and include two new genotypes that are sensitive to metalaxyl.

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Characterization of Isolates of Phytophthora infestans from Tomato and Potato in North Carolina from 1993 to 1995

Plant Disease ◽

10.1094/pdis.1999.83.7.633 ◽

1999 ◽

Vol 83 (7) ◽

pp. 633-638 ◽

Cited By ~ 26

Author(s):

Dawn E. Fraser ◽

Paul B. Shoemaker ◽

Jean B. Ristaino

Keyword(s):

North Carolina ◽

South Carolina ◽

Phytophthora Infestans ◽

Mating Type ◽

The United States ◽

Western North Carolina ◽

New Genotype ◽

The Us ◽

Eastern North Carolina ◽

Allozyme Genotype

Eighty-five isolates of Phytophthora infestans from 33 tomato and 8 potato fields in North Carolina, South Carolina, and Tennessee were collected from 1993 to 1995 and tested for mating type, sensitivity to metalaxyl, and allozyme genotype at glucose-6-phosphate isomerase (Gpi) and peptidase (Pep) loci. One isolate collected from potato in eastern North Carolina in 1994 was the A1 mating type, whereas all other isolates from potato and tomato were the A2 mating type. Six isolates were sensitive to metalaxyl (<40% growth at 1.0 μg of metalaxyl per ml), nineteen isolates were intermediate in sensitivity to metalaxyl (>40% growth at 1.0 μg of metalaxyl per ml and <40% growth at 100 μg of metalaxyl per ml), and sixty isolates were resistant to metalaxyl (<40% growth at 1.0 and 100 μg of metalaxyl per ml). Four different allozyme genotypes at the Gpi and Pep loci were identified. The single A1 isolate found on potato in eastern North Carolina had the dilocus allozyme genotype Gpi 86/100, Pep 92/100 and was identified as the US-1 genotype. Fifty-five isolates had the dilocus allozyme genotype Gpi 100/111, Pep 100/100 and were classified as the US-7 genotype, whereas twenty-four isolates were Gpi 100/111/122, Pep 100/100 and were classified as the US-8 genotype. Two isolates that were sensitive to meta-laxyl and seventeen isolates that were intermediate in sensitivity to metalaxyl were found among the US-7 and US-8 genotypes. In addition, five isolates had the allozyme genotype Gpi 100/100, Pep 92/100 (similar to the previously reported US-6 genotype), but they were the A2 mating type and either sensitive or intermediate in response to metalaxyl. These isolates composed a new genotype not previously reported in the United States and were designated as US-18. The US-7 genotype was more frequent on tomato in western North Carolina and the US-8 genotype was present on potato in eastern North Carolina, indicating that different inoculum sources are responsible for epidemics on the two crops in different regions of the state.

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Classifying the Relative Host Reaction in Potato Cultivars and Breeding Lines to the US-8 Strain of Phytophthora infestans in Minnesota

Plant Disease ◽

10.1094/pdis.2003.87.8.983 ◽

2003 ◽

Vol 87 (8) ◽

pp. 983-990 ◽

Cited By ~ 8

Author(s):

J. C. Jenkins ◽

R. K. Jones

Keyword(s):

Late Blight ◽

Phytophthora Infestans ◽

Rank Correlation ◽

The United States ◽

Spearman Rank Correlation ◽

Breeding Lines ◽

Spearman Rank ◽

Progress Curve ◽

Tuber Blight ◽

The Us

A total of 32 commercial cultivars grown in the United States and 15 potato breeding lines and non-U.S. cultivars were evaluated at Rosemount, MN for their reaction to the US-8 strain of Phytophthora infestans. Commercial red-, russet-, and white-skinned cultivars tested in the commercial cultivar trial (COMC) in 1996 and 1997 were susceptible (S) to moderately susceptible (MS) to this organism, except for Elba, which ranked as moderately resistant (MR). Yellow-fleshed cvs. Hertha, Santé, and Agria were screened in the late blight nursery (LB1) in 1997 and 1998 and classified as S to MS while Island Sunshine, Brador, and Aziza were classified as MR. The Scottish breeding line G6582-3 and U.S. breeding lines A90586-11, AWN86514-2, AWN85624-5, B0692-4, B0718-3, and B0767-2 were classified as resistant (R). Comparison among entries was based on the area under the disease progress curve (AUDPC). Spearman rank correlation for AUDPC in the 1996 and 1997 COMC trials at 14 to 18 days after inoculation (r = 0.65, P < 0.01) was greater than any other interval tested. The Spearman rank correlation for AUDPC in the 1997 and 1998 LB1 trials at 14 to 18 days after inoculation was r = 0.87, P < 0.01 and increased only slightly in successive assessment dates, suggesting that, in Minnesota, effective evaluation of the foliar infection of late blight can occur at 18 days after inoculation or later. The average tuber blight incidence for the COMC trials at harvest was 10.0% in 1996 and 9.7% in 1997. The average tuber blight incidence for the LB1 trials at harvest was 4.3% in 1997 and 14.6% in 1998. Pearson correlations between tuber blight incidence and foliar disease for the COMC trials was very low; however, for the LBl trials, it was significant in both 1997 (r = 0.53, P < 0.01) and 1998 (r = 0.53, P < 0.01). Asymptomatic tubers harvested from the COMC trials developed additional tuber blight when stored 28 days at ambient temperatures and still more when stored for another 5 months at 5°C. Surviving tubers of nine entries were planted in field trials during 1997 and 1998 to determine if plants that develop from tubers exposed to P. infestans could manifest late blight in the subsequent season. Late blight failed to develop throughout the trials in either year.

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Recent Genotypes of Phytophthora infestans in the Eastern United States Reveal Clonal Populations and Reappearance of Mefenoxam Sensitivity

Plant Disease ◽

10.1094/pdis-03-11-0156-re ◽

2012 ◽

Vol 96 (9) ◽

pp. 1323-1330 ◽

Cited By ~ 71

Author(s):

Chia-Hui Hu ◽

Frances G. Perez ◽

Ryan Donahoo ◽

Adele McLeod ◽

Kevin Myers ◽

...

Keyword(s):

United States ◽

New York ◽

North Carolina ◽

Phytophthora Infestans ◽

Eastern United States ◽

Ras Gene ◽

Eastern Canada ◽

Commercial Potato ◽

Close Proximity ◽

The Us

Isolates of Phytophthora infestans (n = 178) were collected in 2002 to 2009 from the eastern United States, Midwestern United States, and eastern Canada. Multilocus genotypes were defined using allozyme genotyping, and DNA fingerprinting with the RG-57 probe. Several previously described and three new mulitilocus genotypes were detected. The US-8 genotype was found commonly on commercial potato crops but not on tomato. US-20 was found on tomato in North Carolina from 2002 through 2007 and in Florida in 2005. US-21 was found on tomato in North Carolina in 2005 and Florida in 2006 and 2007. US-22 was detected on tomato in 2007 in Tennessee and New York and became widespread in 2009. US-22 was found in 12 states on tomato and potato and was spread on tomato transplants. This genotype accounted for about 60% of all the isolates genotyped. The US-23 genotype was found in Maryland, Virginia, Pennsylvania, and Delaware on both tomato and potato in 2009. The US-24 genotype was found only in North Dakota in 2009. A1 and A2 mating types were found in close proximity on potato and tomato crops in Pennsylvania and Virginia; therefore, the possibility of sexual reproduction should be monitored. Whereas most individuals of US-8 and US-20 were resistant to mefenoxam, US-21 appeared to be intermediately sensitive, and isolates of US-22, US-23, and US-24 were largely sensitive to mefenoxam. On the basis of sequence analysis of the ras gene, these latter three genotypes appear to have been derived from a common ancestor. Further field and laboratory studies are underway using simple sequence repeat genotyping to monitor current changes in the population structure of P. infestans causing late blight in North America.

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First Report of Late Blight Caused by Phytophthora infestans Clonal Lineage US-24 on Potato (Solanum tuberosum) in Wisconsin

Plant Disease ◽

10.1094/pdis-09-12-0825-pdn ◽

2013 ◽

Vol 97 (1) ◽

pp. 152-152 ◽

Cited By ~ 6

Author(s):

A. J. Gevens ◽

A. C. Seidl

Keyword(s):

Solanum Tuberosum ◽

Late Blight ◽

Phytophthora Infestans ◽

Weather Conditions ◽

Clonal Lineage ◽

Banding Patterns ◽

First Report ◽

The Us ◽

Epidemiological Characteristics ◽

The U.S

Potato (Solanum tuberosum) crops are grown on over 25,090 ha in Wisconsin annually. Late blight, caused by Phytophthora infestans (Mont.) deBary, is a potentially devastating disease that affects tomato and potato crops in Wisconsin every few years when inoculum is introduced and weather conditions favor disease. Incidence and severity of late blight are highly variable in these few years due to differences in pathogen clonal lineages, their timing and means of introduction, and weather conditions. Prevention of this disease through prophylactic fungicide application can cost producers millions of dollars annually in additional chemical, fuel, and labor expenses. Populations of P. infestans in the U.S. have recently undergone significant genetic change, resulting in isolates with unique clonal lineages and epidemiological characteristics (1). In 2010, late blight epidemics were of low severity in discrete portions of a few fields and were seen exclusively on potato in two counties of central Wisconsin. Symptoms included water-soaked to dark brown circular lesions with pale green haloes accompanied by white fuzzy pathogen sporulation typically on leaf undersides in high humidity conditions. Infected plants were collected by professional crop consultants and submitted to the authors at the University of Wisconsin Vegetable Pathology Laboratory in Madison, Wisconsin. Eight isolates of P. infestans were generated from individual leaf samples, representing separate fields, by removing sporangia from sporulating lesions and placing onto Rye A agar amended with rifampicin and ampicillin. Axenic, single zoospore-derived cultures of isolates were generated from parent cultures and maintained on Rye A agar for further characterization. Mycelium was coenocytic with hyphal diameter of 5 to 8 μm (n = 50). Sporangia were limoniform to ovoid, semi- to fully papillate, caducous, had short pedicels, and were 36.22 × 19.11 μm (height × width; n = 50). The average length-width ratio was 1.91. Allozyme banding patterns at the glucose-6-phosphate isomerase (Gpi) locus indicated a 100/100/111 profile, consistent with the US-24 clonal lineage (3,4). Mating type assays confirmed the isolates to be A1 and intermediate insensitivity to mefenoxam was observed in vitro (4). Genomic DNA was extracted with a phenol:chloroform:isoamyl alcohol solution and restriction fragment length polymorphism (RFLP) analysis was performed using the RG-57 probe on a representative isolate and resulted in banding patterns consistent with US-24 (2,3). Clonal lineages of P. infestans documented in Wisconsin in previous epidemics included US-8 in the mid-1990s and US-1 in the 1970s. The US-24 (A1) clonal lineage was very widespread in the U.S. in 2010 and its presence in Wisconsin in the same year as identification of US-22 (A2) posed great concern for potential sexual recombination, oospore production, and soil persistence. Fortunately, the opposite mating types were separated spatiotemporally. To the best of our knowledge, this is the first report of the P. infestans clonal lineage US-24 causing late blight on potato in Wisconsin. References: (1) K. Deahl. (Abstr.) Phytopathology 100:S161, 2010. (2) S. B. Goodwin et al. Curr. Genet. 22:107, 1992. (3) Hu et al. Plant Dis. 96:1323, 2012. (4) A. C. Seidl and A. J. Gevens. (Abstr.) Phytopathology 101:S162, 2011.

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First Report of the A2 Mating Type of Phytophthora infestans on Tomato Crops in Taiwan, Republic of China

Plant Disease ◽

10.1094/pdis-92-6-0978a ◽

2008 ◽

Vol 92 (6) ◽

pp. 978-978 ◽

Cited By ~ 3

Author(s):

K. L. Deahl ◽

R. W. Jones ◽

L. L. Black ◽

T. C. Wang ◽

L. R. Cooke

Keyword(s):

Phytophthora Infestans ◽

Mating Type ◽

Morphological Characters ◽

Mitochondrial Haplotype ◽

Clonal Lineage ◽

First Report ◽

Test Isolate ◽

The Us ◽

Differential Hosts

In a study of the Phytophthora infestans population in Taiwan, samples with symptoms typical of late blight were collected from field crops in an important potato- (Solanum tuberosum) and tomato-(Lycopersicon esculentum) production area in the central highlands region. Isolates were obtained by surface disinfecting leaf sections and plating them onto antibiotic-amended rye A agar (1). After subculturing, the pathogen was confirmed as P. infestans on the basis of morphological characters (2). Mating type was determined by co-inoculating unamended rye agar plates with mycelial plugs of the test isolate and a reference P. infestans isolate of either the A1 or A2 mating type (four plates per test isolate, two with different A1, and two with different A2 reference isolates). After incubation (15°C darkness, 7 to 14 days), plates were examined microscopically for the presence of oospores where the colonies interacted. In 2004, one isolate of 200 tested, and in 2006, one isolate of 102 tested, produced oospores only with A1 reference isolates and were concluded to be A2 mating type. In vitro testing showed the two A2 isolates were metalaxyl-resistant (ED50 values >100 mg of metalaxyl per liter on rye grain agar), which is typical of recent P. infestans isolates from potato and tomato in this area (2). Twenty-one single-sporangial isolates from each of the two A2 strains were tested for mating type against two different A1 isolates of P. infestans and confirmed as A2. These isolates were characterized using the techniques described by Deahl et al. (1) and had the allozyme genotype 100/100/111, 100/100 at the loci coding for glucose-6-phosphate isomerase and peptidase, respectively, and were mitochondrial haplotype IIb. This multi-locus genotype is characteristic of recent P. infestans isolates from tomato and potato in Taiwan, but all previous such isolates were A1 mating type and attributed to the US-11 clonal lineage (1). When evaluated on differential hosts, both A2 isolates were tomato race PH-1 and complex potato race R 0,1,2,3,4,7,9,11. RG57 fingerprinting showed that the A2 isolates had fingerprints identical to each other and to A1 P. infestans isolates of the US-11 clonal lineage from tomato in Taiwan (101 011 100 100 110 101 011 001 1). Koch's postulates were completed and the two A2 isolates were found to be highly aggressive on cultivars of potato and tomato. To our knowledge, this is the first report of A2 mating type strains of P. infestans in the field in Taiwan, but currently, their incidence is very low (<1%). One crop from which an A2 isolate was obtained also yielded an A1 isolate, while A1 isolates were obtained from crops in the vicinity of the other. The concurrent presence of the two mating types of P. infestans poses a risk of sexual reproduction and oospore formation in tomato or potato in Taiwan. References: (1) K. L. Deahl et al. Pest Manag. Sci. 58:951, 2002. (2). D. C. Erwin and O. K. Ribeiro, Page 346 in: Phytophthora Diseases Worldwide. The American Phytopathological Society. St. Paul, MN, 1996.

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Implications of Sexual Reproduction for Phytophthora infestans in the United States: Generation of an Aggressive Lineage

Plant Disease ◽

10.1094/pdis.2000.84.7.731 ◽

2000 ◽

Vol 84 (7) ◽

pp. 731-735 ◽

Cited By ~ 95

Author(s):

P. D. Gavino ◽

C. D. Smart ◽

R. W. Sandrock ◽

J. S. Miller ◽

P. B. Hamm ◽

...

Keyword(s):

United States ◽

Phytophthora Infestans ◽

The United States ◽

Mitochondrial Haplotype ◽

Columbia Basin ◽

Clonal Lineage ◽

Large Area ◽

The Us ◽

Sexual Progeny

Phytophthora infestans isolates (n = 26) collected in the Columbia Basin of Oregon and Washington in 1993, which had been characterized previously for mating type, metalaxyl sensitivity, and alleles at the glucose-6-phosphate isomerase locus, were analyzed for nuclear restriction fragment length polymorphism (RFLP) bands detected by probe RG57 and mitochondrial haplotype. Analyses involving the larger set of markers indicated that this group of isolates satisfied expectations of a sexual progeny: they contained much greater genetic diversity than has been reported for most other epidemic populations of P. infestans in the United States and Canada (16 unique multilocus genotypes); both mating types were present in proximity; all possible combinations of alleles occurred at many pairs of polymorphic loci; and two distinct mitochondrial haplotypes were distributed among the isolates. An in vitro laboratory cross involving the putative parents (US-6 and US-7) as parental strains produced progeny with the same general characteristics as the field isolates. Among the field progeny were two genotypes, US-11 and US-16, that had been described previously but from subsequent and largely clonal collections. Isolates obtained from tomatoes (n = 40) and potatoes (n = 7) in 24 counties in California in 1998 were analyzed as described above, and all except one US-8 isolate from potatoes were of the US-11 clonal lineage, consistent with the hypothesis that the US-11 lineage is an especially fit clonal lineage that has survived over time and can dominate pathogen populations over a large area. We conclude that the 1993 Columbia Basin collection represents a sexual progeny that generated the US-11 lineage, and that this lineage is particularly fit when tomatoes are part of the agroecosystem.

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Characterization of Phytophthora infestans Populations in Western Washington

Plant Disease ◽

10.1094/pdis.1999.83.5.423 ◽

1999 ◽

Vol 83 (5) ◽

pp. 423-428 ◽

Cited By ~ 29

Author(s):

A. E. Dorrance ◽

D. A. Inglis ◽

M. L. Derie ◽

C. R. Brown ◽

S. B. Goodwin ◽

...

Keyword(s):

Phytophthora Infestans ◽

Mating Type ◽

The United States ◽

Dna Fingerprint ◽

Multilocus Genotype ◽

Sexual Recombination ◽

The Us ◽

Western Washington ◽

Single Field

The first detection in the United States of isolates of Phytophthora infestans having metalaxyl insensitivity and complex pathotypes occurred in western Washington during the early 1990s. To determine the genetic structure of the current population in western Washington, a total of 115 isolates of P. infestans were obtained during 1996 from infected tubers or foliage of potato, tomato, nightshade, and bittersweet throughout the region. An additional 45 isolates were collected from a single field. Based on mating type, metalaxyl-insensitivity, and molecular markers (allozymes of glucose-6-phosphate isomerase, peptidase, and RG57 DNA fingerprint), all of the isolates were A1 mating type and had the US-11 multilocus genotype. Analyses of an additional 120 isolates collected during 1997 from potato, tomato, and nightshade were performed. As in 1996, US-11 was the predominant genotype detected on all three hosts. However, three additional A2 mating type genotypes were also detected: US-7, US-8, and US-14. These three genotypes represent the first A2 mating type isolates detected in western Washington. Most of a subset of 60 isolates infected 4 to 7 of the 10 potato differentials tested. This included 90% of the isolates collected in 1996 (all US-11), plus 72% of the US-11 and 100% of the US-8 and US-14 isolates collected during 1997. Virulence phenotypes in this region are complex even without the selection pressure of R-genes in the local commercial cultivars. The apparent increase in genetic variation observed in populations of P. infestans in western Washington from 1996 to 1997 most likely occurred by migration rather than by sexual recombination.

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Stability in Population of Phytophthora infestans Attacking Tomato in Ecuador Demonstrated by Cellulose Acetate Assessment of Glucose-6-Phosphate Isomerase

Plant Disease ◽

10.1094/pdis.2000.84.3.325 ◽

2000 ◽

Vol 84 (3) ◽

pp. 325-327 ◽

Cited By ~ 3

Author(s):

Lynn J. Erselius ◽

Miguel E. Vega-Sánchez ◽

Gregory A. Forbes

Keyword(s):

Phytophthora Infestans ◽

Cellulose Acetate ◽

Potato Field ◽

Clonal Lineage ◽

Cellulose Acetate Electrophoresis ◽

Banding Patterns ◽

Close Proximity ◽

The Us ◽

Exhaustive Study ◽

Relative Migration

Cellulose acetate electrophoresis was used to examine glucose-6-phosphate (Gpi) isomerase banding patterns of the population of Phytophthora infestans attacking tomato in Ecuador. All but two of 160 sporulating lesions from tomato leaflets collected from 25 tomato fields between January 1998 and March 1999 produced the 86/100 Gpi isozyme electromorph. This isozyme type is characteristic of the US-1 clonal lineage, indicating that no change in the population of P. infestans attacking tomato in Ecuador has occurred since a more exhaustive study was done using isolates collected between 1993 and 1995. The two lesions that produced a different Gpi electromorph in the current study came from a field that was located approximately 80 m from a potato field that had been severely affected by late blight. These two isolates produced a single large band for Gpi with a relative migration distance of 100. This electromorph is characteristic of the clonal lineage EC-1, which was shown previously to be the predominant clonal lineage attacking potato in Ecuador. Therefore, we assume that the two tomato lesions with the EC-1 phenotype were caused by inoculum originating from the potato field. During the current study, 34 infected potato leaflets were collected from five potato fields found in close proximity to blighted tomato fields. All of the potato leaflets produced banding patterns characteristic of EC-1. Our data are consistent with earlier studies indicating that, in Ecuador, tomato and potato are attacked by separate populations of P. infestans, which belong to two different clonal lineages.

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