Characterization of South African Isolates of Phytophthora infestans

Severe late blight epidemics in South Africa in 1995 and 1996 prompted an investigation into the mating type, genotype, and metalaxyl sensitivity of populations of Phytophthora infestans. A country-wide survey was conducted from 1996 to 1998 in which isolates were collected from 101 potato fields (656 isolates) and 16 tomato fields (57 isolates). Six hundred and fifty-seven isolates (600 potato and 57 tomato) were analyzed for mating type, while subsets of isolates were analyzed for genotype at the Glucose-6-phosphate isomerase locus (n = 148), DNA fingerprinting with probe RG-57 (n = 61) and mitochondrial DNA haplotype (n = 20). All isolates tested had the characteristics typical of the pre-1980 population (A1 mating type, 86/100 Gpi genotype, US-1 fingerprint pattern, and mtDNA haplotype I-b) previously found worldwide. Metalaxyl sensitivity testing of 656 potato isolates by the in vitro leaf disk method showed that the frequency of highly resistant isolates (50% effective concentration [EC50] > 200 μg a.i./ml) in potato production regions increased from 35% in 1996 to 51% in 1997. The high frequency of resistant isolates was confined to the southern coastal regions in 1996 and 1997, as well as the western Free State in 1997. Although phenylamides were withdrawn from the southern coastal region in December 1996, screening tests carried out in 1998 indicated that resistance levels remained high (≥83%). Sensitive isolates (EC50 < 40 μg a.i./ml) predominated in the remaining six potato production regions. Screening of 45 isolates collected from tomatoes indicated that no resistant strains were present in the sample tested.

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Biocontrol Activity of Three Pseudomonas in a Newly Assembled Collection of Phytophthora infestans Isolates

Phytopathology ◽

10.1094/phyto-12-18-0487-r ◽

2019 ◽

Vol 109 (9) ◽

pp. 1555-1565 ◽

Cited By ~ 4

Author(s):

Mout De Vrieze ◽

Ramona Gloor ◽

Josep Massana Codina ◽

Stefano Torriani ◽

Katia Gindro ◽

...

Keyword(s):

Phytophthora Infestans ◽

Leaf Disc ◽

Potato Production ◽

Biocontrol Activity ◽

General Demand ◽

Resistant Genotypes ◽

Highly Virulent ◽

Alternative Control Methods ◽

Open Access Article

Late blight caused by the oomycete Phytophthora infestans constitutes the greatest threat to potato production worldwide. Considering the increasing concerns regarding the emergence of novel fungicide-resistant genotypes and the general demand for reducing inputs of synthetic and copper-based fungicides, the need for alternative control methods is acute. Several bacterial antagonists have shown anti-Phytophthora effects during in vitro and greenhouse experiments. We report the effects of three Pseudomonas strains recovered from field-grown potatoes against a collection of P. infestans isolates assembled for this study. The collection comprised 19 P. infestans isolates of mating types A1 and A2 greatly varying in fungicide resistance and virulence profiles as deduced from leaf disc experiments on Black’s differential set. The mycelial growth of all P. infestans isolates was fully inhibited when co-cultivated with the most active Pseudomonas strain (R47). Moreover, the isolates reacted differently to exposure to the less active Pseudomonas strains (S19 and R76). Leaf disc infection experiments with six selected P. infestans isolates showed that four of them, including highly virulent and fungicide-resistant ones, could be efficiently controlled by different potato-associated Pseudomonas strains. [Formula: see text] Copyright © 2019 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

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Nuclear DNA content, mating type and metalaxyl sensitivity of eighty-three isolates of Phytophthora infestans from The Netherlands

Mycological Research ◽

10.1016/s0953-7562(89)80002-4 ◽

1989 ◽

Vol 92 (2) ◽

pp. 140-146 ◽

Cited By ~ 25

Author(s):

C. Dale Therrien ◽

Donna L. Ritch ◽

Leen C. Davidse ◽

Ad B.K. Jespers ◽

Linda J. Spielman

Keyword(s):

The Netherlands ◽

Phytophthora Infestans ◽

Mating Type ◽

Dna Content ◽

Nuclear Dna ◽

Nuclear Dna Content ◽

Metalaxyl Sensitivity

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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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Population Genetic Structure of Phytophthora infestans in Ecuador

Phytopathology ◽

10.1094/phyto.1997.87.4.375 ◽

1997 ◽

Vol 87 (4) ◽

pp. 375-380 ◽

Cited By ~ 80

Author(s):

Gregory A. Forbes ◽

Ximena C. Escobar ◽

Catalina C. Ayala ◽

Jorge Revelo ◽

Maria E. Ordoñez ◽

...

Keyword(s):

Genetic Structure ◽

Phytophthora Infestans ◽

Mating Type ◽

Population Genetic Structure ◽

Population Genetic ◽

Nuclear Dna ◽

Dna Fingerprint ◽

Clonal Lineage ◽

Metalaxyl Sensitivity ◽

Neutral Markers

The population genetic structure of Phytophthora infestans in Ecuador was assessed from 101 isolates collected from 1990 to 1992 and 111 isolates collected in 1993. All isolates were analyzed for mating type and allozyme genotype. Both samples were dominated (>95%) by a clonal lineage (EC-1) defined from neutral markers: 90/100 genotype for glucose-6-phosphate isomerase, 96/100 genotype for peptidase, A1 mating type, and a previously unreported nuclear DNA fingerprint. The remaining isolates belonged to the US-1 clonal lineage, which has a worldwide distribution. Isolates in the 1993 sample were analyzed for virulence and metalaxyl sensitivity. All representatives of EC-1 had complex patho-types, with three pathotypes representing >60% of the collection. There was variation for metalaxyl sensitivity. There was no evidence for geographical substructuring on the basis of neutral markers, but there was evidence for limited substructuring based on metalaxyl sensitivity and specific virulence. We hypothesize that EC-1 has been recently introduced to Ecuador.

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Infection of Potatoes by Oospores of Phytophthora infestans in Soil

Plant Disease ◽

10.1094/pdis.1999.83.9.876c ◽

1999 ◽

Vol 83 (9) ◽

pp. 876-876 ◽

Cited By ~ 11

Author(s):

A. Strömberg ◽

L. Persson ◽

M. Wikström

Keyword(s):

Late Blight ◽

Phytophthora Infestans ◽

Mating Type ◽

Potato Crop ◽

Selective Medium ◽

Day Length ◽

Talcum Powder ◽

Soil P ◽

Nodal Cuttings

Phytophthora infestans (Mont.) de Bary, causing late blight on potatoes and considered to be a typical airborne disease, was found to be infective also by oospores in the soil. P. infestans is heterothallic, and is known to reproduce asexually in Sweden since only one mating type, A1, was present until 1986. Since the 1970s, the other mating type, A2, of P. infestans has migrated to most parts of the world from its original location in central Mexico (2). When A1 and A2 meet, they may form oospores, which are thick-walled, resting structures, giving the pathogen a possibility to recombine as well as survive without its host, for instance in the soil. The soil stages of the pathogen are now therefore under intense investigation. Oospores of P. infestans were produced from two Scandinavian A1 and A2 isolates in Rye A broth mixed with talcum powder and dried for 7 weeks. The inoculum was mixed with sterile, standardized soil in concentrations of 10, 150, 250, and 400 oospores per ml of soil. Cv. Bintje plants cultivated in vitro from nodal cuttings on Murashige and Skoog medium were transplanted to the soil after rooting. Brown discolorations were obtained on the underground stems and tubers on potato plants grown in the two highest concentrations of oospores for 1 month at 15°C and 16-h day length. After 3 days of incubation on P. infestans-selective medium (3), sporangia covered the tissue from plants grown in 250 and 400 oospores per ml of soil and the pathogen was reisolated. This shows that germinating oospores of P. infestans can infect underground stems and tubers of potatoes in soil and further explains the early attack of late blight as observed in a potato crop in Sweden 1996 and 1997 (1). References: (1) B. Andersson et al. Potato Res. 41:305, 1998. (2) D. Andrivon. Phytopathology 85:1053, 1995. (3) G. W. Griffith et al. Mycologist 9:87, 1995.

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Environmental and Genetic Factors Influencing Self-Fertility in Phytophthora infestans

Phytopathology ◽

10.1094/phyto.2000.90.9.987 ◽

2000 ◽

Vol 90 (9) ◽

pp. 987-994 ◽

Cited By ~ 11

Author(s):

C. D. Smart ◽

H. Mayton ◽

E. S. G. Mizubuti ◽

M. R. Willmann ◽

W. E. Fry

Keyword(s):

Phytophthora Infestans ◽

Mating Type ◽

Leaf Tissue ◽

Single Individual ◽

Oatmeal Agar ◽

Physical Proximity ◽

Type Isolate ◽

In Vivo Tests

Phytophthora infestans is generally regarded as heterothallic-requiring physical proximity of two individuals of different mating type (A1 and A2) for oosporogenesis. Recent reports of limited selfing in young cultures of this oomycete stimulated us to investigate factors contributing to the phenomenon. The ability to produce oospores rapidly (within 2 weeks) in pure, single individual cultures (self-fertility) was tested in 116 individual isolates. The 116 isolates were from geographically diverse locations (16 countries) and were genetically diverse. Mating type and growth medium were the most prominent factors in determining if an isolate would be self-fertile. The majority of A2 isolates (45 of 47 tested) produced oospores when grown on a 50:50 mixture of V8 and rye B medium. In contrast, the majority of A1 isolates (65 of 69 tested) did not produce oospores on this medium. None of the 116 isolates produced oospores when grown on rye B medium (with no V8 juice). Further tests on representative A1 and A2 isolates revealed that oatmeal agar, tomato juice agar, and V8-juice agar all induced the A2 mating type isolate to produce oospores but did not induce the A1 mating type isolate to produce oospores. Calcium carbonate and pH did not alter the self-fertile oospore production in either A1 or A2 mating type isolates. For in vivo tests, the application of fungicide to potato or tomato leaf tissue either before or after inoculation did not stimulate any individual isolate (one A2 and one A1 isolate) to produce oospores in infected tissue. However, in all of the controls for all experiments (in vivo and in vitro), many oospores were produced rapidly if both strains grew in physical proximity.

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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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Commercial Fungicide Formulations Induce In Vitro Oospore Formation and Phenotypic Change in Mating Type in Phytophthora infestans

Phytopathology ◽

10.1094/phyto.2000.90.11.1201 ◽

2000 ◽

Vol 90 (11) ◽

pp. 1201-1208 ◽

Cited By ~ 30

Author(s):

Carol Trout Groves ◽

Jean Beagle Ristaino

Keyword(s):

Late Blight ◽

Phytophthora Infestans ◽

Mating Type ◽

Petri Dish ◽

Phenotypic Change ◽

Tomato Production ◽

Wide Range ◽

Oospore Formation ◽

Commercial Fungicide

A wide range of commercially formulated fungicides cause in vitro effects on mating behavior in specific isolates of Phytophthora infestans, the causal agent of late blight of potato and tomato. Four isolates of P. infestans representing each of the four common US genotypes, US-1, US-6, US-7, and US-8 and varying in their sensitivity to metalaxyl, were exposed to a variety of fungicides used to control late blight in petri dish assays at concentrations ranging from 1 to 100 μg a.i./ml. Exposure of each of these normally heterothallic single mating type isolates of P. infestans to 9 of the 11 commercial fungicide formulations tested resulted in the formation of oospores after 2 to 4 weeks. The highest numbers of oospores were formed on media amended with Ridomil 2E (metalaxyl) and Ridomil Gold EC (mefenoxam) at 0.1 to 10 μg a.i./ml, averaging as many as 471 and 450 oospores per petri dish, respectively. Several other fungicides including Maneb, Manzate (Mancozeb), Curzate (cymoxanil + mancozeb), and Acrobat MZ (dimethomorph + mancozeb) also induced oospore formation, producing from 0 to 200 oospores per plate at fungicide concentrations from 0.1 to 10 μg a.i./ml. The metalaxyl resistant isolates formed oospores in response to the fungicides more often than the metalaxyl sensitive isolates. No oospores were formed on media amended with Bravo (chlorothalonil) or Tattoo C (chlorothalonil + propamocarb HCl) and these compounds completely suppressed growth of the isolates at 0.1 and 1 μg a.i./ml. Three metalaxyl resistant A2 isolates mated with both A1 and A2 isolates after exposure to the fungicides Ridomil 2E and Ridomil Gold EC. Alterations in mating type expression were also observed in a metalaxyl sensitive A1 isolate after exposure to Benlate (benomyl). Copious amounts of chemicals are applied annually to potato and tomato production areas to control late blight. Our results indicate that a wide range of chemically diverse fungicides can induce normally heterothallic metalaxyl resistant isolates of P. infestans to form oospores in vitro after short exposures to the fungicides.

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The Potency of Unassociated Trichoderma spp and the Fungicides Antagonistic of the Late Blight of Potato by Phytophthora infestans (Mont.) De-Bary

International Journal of Plant & Soil Science ◽

10.9734/ijpss/2021/v33i1630542 ◽

2021 ◽

pp. 246-253

Author(s):

Anuj Bansal ◽

S. K. Biswas ◽

Deepak Baboo ◽

Vikram Singh

Keyword(s):

Late Blight ◽

Phytophthora Infestans ◽

Radial Growth ◽

Potato Production ◽

Dual Culture ◽

Vegetable Crops ◽

Culture Methods ◽

Trichoderma Spp ◽

Late Blight Of Potato

The potato (Solanum tuberosum) is one of the most important vegetable crops in the world, belonging to the family Solanaceae and is an important starchy food crop in both sub-tropical and temperate regions. Potato plants are subjected to attack by numerous diseases wherever the crop is grown. Among them, late blight of potato caused by Phytophthora infestans (Mont.) de-Bary is of major cause of concern in potato production at present. An experiment was conducted in the Department of Plant Pathology, College of Agriculture, Chandra Shekhar Azad University of Agriculture and Technology, Kanpur. The antifungal activity of different fungicides was evaluated in-vitro through the food poison technique. The experimental finding showed that radial growth of mycelium of Phytophthora infestans was inhibited by fungicides over control. At 100 ppm, the minimum radial growth of mycelium was found in Equation Pro treatment as 5.3, 8.2, 11.4, 14.2, 16.2, 18.4 and 22.6 mm over control against 12.3, 19.1, 26.1, 35.9, 42.5, 51.4 and 64.8 mm at 1, 2, 3, 4, 5, 6 and 7 days after inoculation respectively. Similarly, at 500 and 1000 ppm the minimum radial growth of mycelium was found in Equation Pro treatment. Efficacy of bio-control agents on the radial growth of Phytophthora infestans was evaluated using Dual Culture Methods. Among the different concentrations, 1000 ppm was found most effective than 100 and 500 ppm. Among the different bio-agents, Trichoderma harzianum able to reduced maximum radial mycelial growth of fungus showing 4.6, 8.8, 10.1, 13.2, 15.6, 19.3 and 23.5 mm against 12.3, 19.1, 26.1, 35.9, 42.5, 51.4 and 64.8 mm at 1, 2, 3, 4, 5, 6 and 7 days after inoculation, respectively.

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Mutagenesis of Phytophthora infestans for Resistance Against Carboxylic Acid Amide and Phenylamide Fungicides

Plant Disease ◽

10.1094/pdis-92-5-0675 ◽

2008 ◽

Vol 92 (5) ◽

pp. 675-683 ◽

Cited By ~ 20

Author(s):

Avia (Evgenia) Rubin ◽

Dror Gotlieb ◽

Ulrich Gisi ◽

Yigal Cohen

Keyword(s):

Carboxylic Acid ◽

Phytophthora Infestans ◽

Mating Type ◽

Uv Light ◽

Acid Amide ◽

Late Blight Resistance ◽

Plasmopara Viticola ◽

Carboxylic Acid Amide ◽

In Planta

The carboxylic acid amide (CAA) fungicides mandipropamid, dimethomorph, iprovalicarb, and the phenylamide fungicide mefenoxam (MFX, the active enantiomer of metalaxyl) are anti-oomycete fungicides effective against downy mildews and late blight. Resistance against MFX was reported in nature in several oomycetes including Phytophthora infestans and Plasmopara viticola, whereas resistance against CAAs was reported in P. viticola but not in P. infestans. In this study the mutability of P. infestans for resistance against CAAs and MFX (as a control) was explored under laboratory conditions. UV light or chemical mutagens (e.g., ethyl methan sulfonate [EMS]) were applied to sporangia, and the emergence of mutants resistant to CAAs or MFX, or with altered mating type, was followed. Many mutants resistant to CAAs developed at generation 0 after mutagenesis, but all showed erratic, instable resistance in planta, diminishing after 1 to 8 asexual infection cycles, and failed to grow on CAA-amended medium. In contrast, 19 mutants resistant to MFX were obtained: 6 with UV irradiation (in isolates 28 or 96) and 13 with EMS (in isolates 408, 409, and 410). In three experiments, a shift in mating type, from A1 to A2, was detected. To elucidate whether or not resistance to CAAs is recessive and therefore might emerge only after sexual recombination, A1 and A2 mutants were crossed and the F1 and F2 progeny isolates were tested for resistance. Offspring isolates segregated for resistance to MFX, with resistant isolates maintaining stable resistance in vitro and in planta, whereas all progeny isolates failed to show stable resistance to CAAs in planta or in vitro. The data suggest that P. infestans could be artificially mutated for resistance against MFX, but not against CAAs.

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