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

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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Mefenoxam Sensitivity in US-8 and US-23 Phytophthora infestans from Wisconsin

Plant Health Progress ◽

10.1094/php-02-21-0044-fi ◽

2021 ◽

Author(s):

Eric R. Larson ◽

Lukas E. Migliano ◽

Yu Chen ◽

Amanda J. Gevens

Keyword(s):

Phytophthora Infestans ◽

Mating Type ◽

Systemic Fungicide ◽

Clonal Lineage ◽

Best Management ◽

Growing Seasons ◽

The Us ◽

Management Approaches ◽

The One ◽

Ongoing Monitoring

The contemporary dominant clonal lineage of heterothallic Phytophthora infestans in Wisconsin, US-23, is classified as sensitive to the systemic fungicide mefenoxam and is of the A1 mating type. With the sporadic appearance of clonal lineage US-8, classified as resistant to mefenoxam and of the A2 mating type, there is a need for ongoing monitoring and characterization. Isolates of P. infestans collected from Wisconsin during the 2017 and 2018 growing seasons were tested for sensitivity to mefenoxam with discriminatory dose of 100 ppm. In 2017, both US-23 and US-8 were isolated. On average, isolates of US-23 were significantly more sensitive to mefenoxam than were US-8 isolates (P = 8e-04). There were significant differences in the sensitivity levels among the US-8 isolates (P = 2.02e-06), with a single isolate testing sensitive at 100 ppm of mefenoxam based on the one-way ANOVA. There were significant differences in the sensitivity levels among US-23 isolates (P = 3.75e-09), with two isolates showing resistance. In 2018 only US-23 was found, and isolates were tested for mefenoxam response at 0, 0.1, 1, 10, and 100 ppm. At 0.1 ppm, isolates showed significantly different levels of sensitivity (P = 2.1e-09), and a single isolate showed complete resistance. Isolates from both clonal lineages and years that exhibited moderate levels of resistance had greater variability among replicates. The phenotype of this multigenic trait comes through in the variability seen in isolates that are showing more resistance. Continued screening of P. infestans for mefenoxam sensitivity will help track the development and mechanism of resistance, as well as aid in development of best management approaches.

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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 Haplotype I-b of Phytophthora infestans in Central Mexico

Plant Disease ◽

10.1094/pdis-91-7-0909b ◽

2007 ◽

Vol 91 (7) ◽

pp. 909-909 ◽

Cited By ~ 3

Author(s):

E. Garay-Serrano ◽

S. P. Fernández-Pavía ◽

G. Rodríguez-Alvarado ◽

W. G. Flier ◽

H. Lozoya-Saldaña ◽

...

Keyword(s):

Phytophthora Infestans ◽

Mating Type ◽

Central Mexico ◽

Phenotypic Characteristics ◽

First Report ◽

Extensive Search ◽

The Us ◽

Reference Strains ◽

Single Lesion ◽

Mtdna Haplotype

Central Mexico is considered a center of genetic diversity for Phytophthora infestans on the basis of a range of genotypic and phenotypic characteristics (3). Surprisingly, while mitochondrial DNA (mtDNA) haplotypes I-a, II-a, and II-b have been reported from central Mexico, haplotype I-b has not been found in central Mexico (1). Therefore, a more extensive search for haplotypes was conducted in areas where sexual reproduction occurs. During the summer of 2003, leaflets of cvs. Rosita and Tollocan with a single lesion of late blight were collected in the area of Villarreal, located in Terrenate County in Tlaxcala, Mexico (170 km northeast of Mexico City). Fourteen P. infestans isolates were characterized for mtDNA haplotype, isozyme genotype (glucose 6- phosphate isomerase [Gpi] and peptidase [Pep]), and mating type. Isolation, mating type, and isozyme genotype were characterized following reported protocols (1,4). MtDNA haplotype was determined by amplifying and digesting the P2 and P4 regions and comparing amplicons to those of reference strains of known haplotype (1,2). Twelve isolates were mtDNA haplotype I-a and two were I-b. While the mtDNA I-b has been associated with the US-1 lineage (mating type: A1, Gpi: 86/100, Pep: 92/100), the genotypes for the Mexican isolates were A2, 86/100 Gpi, 100/100 Pep from cv. Rosita and A2, 86/100 Gpi, 92/100 Pep from cv. Tollocan. To our knowledge, this is the first report of the I-b mtDNA haplotype of P. infestans from central Mexico and it is now clear that all four haplotypes exist in Mexico. This finding therefore, stresses the importance of including a representative regional sampling of Mexican and Andean isolates in studies inferring the origin of this species. References: (1) W. G. Flier et al. Phytopathology 93:382, 2003. (2) G. W. Griffith and D. S. Shaw. Appl. Environ. Microbiol. 64:4007, 1998. (3) N. J. Grünwald and W. G. Flier. Ann. Rev. Phytopathol. 43:171, 2005. (4) N. J. Grünwald et al. Phytopathology 91:882, 2001.

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First Report of Late Blight Caused by Phytophthora infestans Clonal Lineage US-22 on Tomato and Potato in Wisconsin

Plant Disease ◽

10.1094/pdis-08-12-0807-pdn ◽

2013 ◽

Vol 97 (3) ◽

pp. 423-423 ◽

Cited By ~ 1

Author(s):

A. J. Gevens ◽

A. C. Seidl

Keyword(s):

Late Blight ◽

Phytophthora Infestans ◽

Average Length ◽

The State ◽

Width Ratio ◽

Clonal Lineage ◽

First Report ◽

Hyphal Diameter ◽

Epidemiological Characteristics

Tomato (Solanum lycopersicum) and potato (S. tuberosum) crops are grown on over 67,000 acres (27,114 hectares) in the state of Wisconsin each year. Late blight, caused by Phytophthora infestans (Mont.) deBary, is a potentially devastating oomycete pathogen that sporadically affects tomato and potato crops in the state. Prevention of this disease through prophylactic application of oomycete-specific fungicides can cost producers millions of dollars per year in additional chemical, fuel, and labor expenses. In 2009, late blight was observed on tomato and potato in over 25 Wisconsin counties. The epidemic initiated on tomato in southern WI in early August and progressed northward in the state with additional reports on tomato primarily from home gardens and small farms. Potato late blight was also identified but with limited incidence in central WI, likely due to routine fungicide programs in commercial production. Clonal lineages of P. infestans documented in Wisconsin in previous epidemics included US-1 in the 1970s and US-8 in the mid-1990s. Populations of P. infestans in the U.S. have recently undergone significant genetic changes, resulting in isolates with unique clonal lineages and epidemiological characteristics (1). Symptoms of late blight observed on tomato and potato included water-soaked to dark brown circular lesions with pale green haloes accompanied by signs of pathogen sporulation typically on leaf undersides during periods of high humidity. Isolates of P. infestans were generated from field infected tomato and potato foliar tissues. Axenic, single zoospore derived cultures were generated 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 or ovoid, semi- to fully papillate, caducous, had short pedicels, and were 29.6 (h) × 16.8 μm (w) (n = 50). The average length/width ratio was 1.76. Allozyme banding patterns at the glucose-6-phosphate isomerase (Gpi) locus indicated a 100/122 profile, consistent with the US-22 clonal lineage (3). Mating type assays confirmed the isolates to be A2 and in vitro mefenoxam sensitivity was observed (4). Restriction fragment length polymorphic analysis of a representative isolate from Wisconsin with the multilocus RG57 sequence and EcoRI produced the DNA pattern indicative of US-22 (2). The P. infestans clonal lineage US-22 was predominant in U.S. epidemics on tomato in 2009. To our knowledge, this is the first report of P. infestans clonal lineage US-22 causing late blight on tomato and potato in Wisconsin, USA. References: (1) K. Deahl. (Abstr.) Phytopathology 100(suppl.):S161, 2010. (2) S. B. Goodwin et al. Curr. Genet. 22:107, 1992. (3) C. H. Hu et al. Plant Dis. 96:1323, 2012. (4) A. C. Seidl et al. Phytopathology 101(suppl.):S246, 2011.

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First Report of Late Blight Caused by Phytophthora infestans Clonal Lineage US-23 on Tomato and Potato in Atlantic Canada

Plant Disease ◽

10.1094/pdis-08-13-0807-pdn ◽

2014 ◽

Vol 98 (3) ◽

pp. 426-426 ◽

Cited By ~ 3

Author(s):

C. P. Wijekoon ◽

R. D. Peters ◽

K. I. Al-Mughrabi ◽

L. M. Kawchuk

Keyword(s):

United States ◽

Late Blight ◽

New Brunswick ◽

Phytophthora Infestans ◽

Mating Type ◽

Prince Edward Island ◽

The United States ◽

Clonal Lineage ◽

Eastern Canada ◽

The Us

Phytophthora infestans (Mont.) de Bary has produced significant losses in potato and tomato yield and quality during recent late blight epidemics in North America. During the 1990s, more aggressive and genetically diverse P. infestans genotypes migrated to Canada and the United States (2). For example, US-8 became predominant and was found to be more aggressive in potato than previous clonal lineages of P. infestans. Recent P. infestans genotypes in potato and tomato plants from the United States and Canada include US-22, US-23, and US-24 representing clonal lineages with unique epidemiological characteristics (2,3,4). Characteristic phenotypic traits have been described for P. infestans clonal lineages US-8, US-22, US-23, and US-24 based on the mating type, mefenoxam sensitivity, pathogenicity, and rate of germination suggesting an association between phenotypic variations and the genotype (1,4). Analysis of P. infestans isolates collected in Canada during 2010 revealed the presence of the US-23 clonal lineage in four different areas of western Canada but not in eastern Canada (4). Isolates of P. infestans collected from eastern Canada for several years prior to 2011 were all US-8 A2 mating type. Isolation and analysis of 98 P. infestans isolates in 2011 from New Brunswick and Prince Edward Island followed standard procedures (2,3,4). Results confirmed the presence of the US-23 clonal lineage in Atlantic Canada on potato and tomato leaves with late blight symptoms, increasing the genetic complexity of P. infestans in eastern Canada. Allozyme banding patterns at the glucose-6-phosphate isomerase (Gpi) locus showed a 100/100 profile in 10 P. infestans isolates, consistent with the US-23 clonal lineage (2,3,4). Furthermore, in vitro mefenoxam sensitivity was observed in all 10 P. infestans US-23 isolates from New Brunswick and Prince Edward Island. Mating type assays confirmed the isolates were of the A1 mating type. RFLP analysis of EcoR1-digested genomic DNA using the multilocus RG57 sequence as a probe produced the DNA pattern 1, 2, 5, 6, 10, 13, 14, 17, 20, 21, 24, 24a, 25, indicative of US-23 (2,4). Microsatellite analysis using polymorphic markers on New Brunswick and Prince Edward Island P. infestans isolates produced the Pi4B 213/217 bp, D13 134 bp, and PiG11 140/155 bp profile of P. infestans US-23 (1). These results show the presence of the P. infestans A1 and A2 mating types in New Brunswick and Prince Edward Island, which increases the probability of sexual recombination. To our knowledge, this is the first report of P. infestans clonal lineage US-23 causing late blight in New Brunswick and Prince Edward Island, increasing the genetic diversity from previous years in eastern Canada and underscoring the annual fluctuation occurring in the population composition. References: (1) G. Danies et al. Plant Dis. 97:873, 2013. (2) S. B. Goodwin et al. Phytopathology 84:553, 1994. (3) C. H. Hu et al. Plant Dis. 96:1323, 2012. (4) M. L. Kalischuk et al. Plant Dis. 96:1729, 2012.

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Fungicide Sensitivity of U.S. Genotypes of Phytophthora infestans to Six Oomycete-Targeted Compounds

Plant Disease ◽

10.1094/pdis-05-14-0452-re ◽

2015 ◽

Vol 99 (5) ◽

pp. 659-666 ◽

Cited By ~ 35

Author(s):

Amanda Saville ◽

Kim Graham ◽

Niklaus J. Grünwald ◽

Kevin Myers ◽

William E. Fry ◽

...

Keyword(s):

United States ◽

Phytophthora Infestans ◽

The United States ◽

Effective Concentration ◽

Response Curves ◽

Baseline Sensitivity ◽

Fungicide Sensitivity ◽

The Past ◽

The Us

Phytophthora infestans causes potato late blight, an important and costly disease of potato and tomato crops. Seven clonal lineages of P. infestans identified recently in the United States were tested for baseline sensitivity to six oomycete-targeted fungicides. A subset of the dominant lineages (n = 45) collected between 2004 and 2012 was tested in vitro on media amended with a range of concentrations of either azoxystrobin, cyazofamid, cymoxanil, fluopicolide, mandipropamid, or mefenoxam. Dose-response curves and values for the effective concentration at which 50% of growth was suppressed were calculated for each isolate. The US-8 and US-11 clonal lineages were insensitive to mefenoxam while the US-20, US-21, US-22, US-23, and US-24 clonal lineages were sensitive to mefenoxam. Insensitivity to azoxystrobin, cyazofamid, cymoxanil, fluopicolide, or mandipropamid was not detected within any lineage. Thus, current U.S. populations of P. infestans remained sensitive to mefenoxam during the displacement of the US-22 lineage by US-23 over the past 5 years.

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Occurrence and distribution of mating types A1 and A2 of Phytophthora infestans (Mont.) de Bary in the Czech Republic

Plant Protection Science ◽

10.17221/2697-pps ◽

2010 ◽

Vol 42 (No. 2) ◽

pp. 41-48 ◽

Cited By ~ 7

Author(s):

J. Mazáková ◽

V. Táborský ◽

M. Zouhar ◽

P. Ryšánek ◽

E. Hausvater ◽

...

Keyword(s):

Czech Republic ◽

Phytophthora Infestans ◽

Mating Type ◽

Mating Types ◽

Pcr Markers ◽

The Czech Republic ◽

First Report

A total of 199 <i>Phytophthora infestans</i> isolates were obtained from leaves, tubers and fruits of infected crops of potato and tomato in different regions of the Czech Republic in 2003, 2004 and 2005. They were analysed for mating type using the conventional pairing assay and PCR markers; 107 isolates were of A1 and 92 of A2 mating type. No self-fertile isolate was found. Our study is the first report of the presence and distribution of the A2 mating type of <i>P. infestans</i> in the Czech Republic. The co-existence of the two mating types may enable the pathogen to reproduce sexually, thus enhancing the diversity of its population countrywide.

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

Phytopathology ◽

10.1094/phyto.2002.92.11.1189 ◽

2002 ◽

Vol 92 (11) ◽

pp. 1189-1195 ◽

Cited By ~ 19

Author(s):

T. Wangsomboondee ◽

C. Trout Groves ◽

P. B. Shoemaker ◽

M. A. Cubeta ◽

J. B. Ristaino

Keyword(s):

North Carolina ◽

Phytophthora Infestans ◽

Mitochondrial Haplotype ◽

Banding Patterns ◽

Tuber Blight ◽

Genetic Diversity And Structure ◽

The Us ◽

Unique Restriction ◽

Single Field ◽

Allozyme Genotype

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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Host Specificity of Phytophthora infestans on Tomato and Potato in Ecuador

Phytopathology ◽

10.1094/phyto.1998.88.3.265 ◽

1998 ◽

Vol 88 (3) ◽

pp. 265-271 ◽

Cited By ~ 69

Author(s):

P. J. Oyarzun ◽

A. Pozo ◽

M. E. Ordoñez ◽

K. Doucett ◽

G. A. Forbes

Keyword(s):

Phytophthora Infestans ◽

Mating Type ◽

Clonal Lineage ◽

Avirulence Genes ◽

Mitochondrial Dna Haplotype ◽

Different Populations ◽

Tomato Cultivars ◽

Globally Distributed ◽

Allozyme Genotype ◽

Specific Virulence

Sixty Ecuadorian isolates of Phytophthora infestans from potato and 60 isolates from tomato were compared for dilocus allozyme genotype, mitochondrial DNA haplotype, mating type, and specific virulence on 11 potato R-gene differential plants and four tomato cultivars, two of which contained different Ph genes. Restriction fragment length polymorphism (RFLP) fingerprints of subsamples of isolates from each host were compared by using RG57 as the probe. All potato isolates had the allozyme genotype, haplotype, and mating type of the clonal lineage EC-1, which had been previously described in Ecuador. With the same markers, only one isolate from tomato was classified as EC-1; all others belonged to the globally distributed US-1 clonal lineage. RFLP fingerprints of isolate subsets corroborated this clonal lineage classification. Specific virulence on potato differentials was broadest among potato isolates, while specific virulence on tomato cultivars was broadest among tomato isolates. Some tomato isolates infected all tomato differentials but no potato differentials, indicating that specific virulence for the two hosts is probably controlled by different avirulence genes in P. infestans. In two separate experiments, the diameters of lesions caused by nine isolates from potato and 10 from tomato were compared on three tomato and three potato cultivars. All isolates produced larger lesions on the host from which they were isolated. No isolates were found that were highly aggressive on both tomato and potato. We conclude that there are two different populations of P. infestans in Ecuador and that they are separated by host.

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