Analysis of internal transcribed spacer (ITS) region of Phytophthora tropicalis causing quick wilt disease of black pepper in Vietnam

Phytophthora quick wilt is a devastating disease of black peppers in Vietnam. The internal transcribed spacer (ITS) region of the ribosomal DNA of four Phytophthora samples isolated from the diseased vines in Daknong province of the central highland part of Vietnam was Polymerase chain reaction-amplified, cloned, sequenced and characterised. Database search have showed that they are most closely related to an isolate of Phytophthora tropicalis from Taiwan. Sequence comparisons and phylogenetic analyses based on the ITS region of the four Vietnamese and other GenBank isolates of P. tropicalis and a closely related species, P. capsici, provide strong evidences that the Vietnamese isolates are all different isolates of P. tropicalis.     

Characterization and pathogenicity of three Phytophthora spp. recovered from rivers in Bulgaria

Many Phytophthora species are pathogens on fruit trees and may cause destructive diseases. In the current study, we examined six Phytophthora isolates recovered from rivers in Bulgaria, representatives of the following three species: Phytophthora chlamydospora, P. pseudocryptogea and P. syringae. Morphological traits, cardinal temperatures and growth rates of the isolates were described. We found considerable variation in the size of sporangia and significant difference in the mycelial growth rates of the two P. pseudocryptogea isolates, along with multiple polymorphic sites in the ITS region of one of them. In the cases of the other two Phytophthora species, no such differences were found between the isolates. Both P. chlamydospora isolates had a lower optimum growth temperature compared with the reported in the literature for this species. In pathogenicity tests against leaves and fruits of apple, pear, cherry, apricot and plum, the isolates proved to be capable of causing infections with varying severity. P. chlamydospora showed to be the most aggressive towards the leaves, while P. pseudocryptogea isolates induced the highest percentage of decay on the fruits of all tested tree species, which may suggest partial organ or tissue specificity. The demonstrated infection capacity of the described isolates points out the investigated Phytophthora species as a potential threat for the orchards in Bulgaria, if favourable conditions are available.     

Development of a PCR Assay for the Molecular Detection of Phytophthora boehmeriae in Infected Cotton

Cotton blight, caused by the oomycete Phytophthora boehmeriae, is a serious disease of cotton in China. In wet weather conditions, P. boehmeriae is usually the primary pathogen, followed by many saprophytic fungi and pathogens such as Pythium spp., Fusarium spp., Rhizoctonia and others. As P. boehmeriae grows much slower than other pathogens, it is difficult to isolate and identify. A rapid and accurate method for its specific identification is necessary for the detection of blight in infected cotton tissue. The internal transcribed spacer (ITS) regions of ribosomal DNA (rDNA) from three isolates of P. boehmeriae were amplified using the polymerase chain reaction (PCR) with the universal primers DC6 and ITS4. PCR products were cloned and sequenced. The sequences were aligned with those published of 50 other Phytophthora species, and a region specific to P. boehmeriae was used to construct the specific PCR primers PB1 and PB2. Over 106 isolates of 14 Phytophthora species and at least 20 other fungal species were used to check the specificity of the primers. PCR amplification with primers PB1 and PB2 resulted in the amplification of a product of approximately 750 bp only from isolates of P. boehmeriae. Using primers PB1 and PB2, detection sensitivity was approximately 10 fg DNA/μl. In inoculated plant material, P. boehmeriae could be detected in tissue 1 day after inoculation, prior to the appearance of symptoms. The PB primer‐based PCR assay provides an accurate and sensitive method for detecting P. boehmeriae in cotton tissue.     

CONSPECIFICITY AND INDO-PACIFIC DISTRIBUTION OF SYMBIODINIUM GENOTYPES (DINOPHYCEAE) FROM GIANT CLAMS

We previously reported the occurrence of genetically‐diverse symbiotic dinoflagellates (zooxanthellae) within and between 7 giant clam species (Tridacnidae) from the Philippines based on the algal isolates' allozyme and random amplified polymorphic DNA (RAPD) patterns. We also reported that these isolates all belong to clade A of the Symbiodinium phylogeny with identical 18S rDNA sequences. Here we extend the genetic characterization of Symbiodinium isolates from giant clams and propose that they are conspecific. We used the combined DNA sequences of the internal transcribed spacer (ITS)1, 5.8S rDNA, and ITS2 regions (rDNA‐ITS region) because the ITS1 and ITS2 regions evolve faster than 18S rDNA and have been shown to be useful in distinguishing strains of other dinoflagellates. DGGE of the most variable segment of the rDNA‐ITS region, ITS1, from clonal representatives of clades A, B, and C showed minimal intragenomic variation. The rDNA‐ITS region shows similar phylogenetic relationships between Symbiodinium isolates from symbiotic bivalves and some cnidarians as does 18S rDNA, and that there are not many different clade A species or strains among cultured zooxanthellae (CZ) from giant clams. The CZ from giant clams had virtually identical sequences, with only a single nucleotide difference in the ITS2 region separating two groups of isolates. These data suggest that there is one CZ species and perhaps two CZ strains, each CZ strain containing individuals that have diverse allozyme and RAPD genotypes. The CZ isolated from giant clams from different areas in the Philippines (21 isolates, 7 clam species), the Australian Great Barrier Reef (1 isolate, 1 clam species), Palau (8 isolates, 7 clam species), and Okinawa, Japan (1 isolate, 1 clam species) shared the same rDNA‐ITS sequences. Furthermore, analysis of fresh isolates from giant clams collected from these geographical areas shows that these bivalves also host indistinguishable clade C symbionts. These data demonstrate that conspecific Symbiodinium genotypes, particularly clade A symbionts, are distributed in giant clams throughout the Indo‐Pacific.     

Genotypic Diversity among Brazilian Isolates of Sclerotium rolfsii

Thirty isolates of Sclerotium rolfsii Sacc. from different hosts and regions of Brazil were studied in relation to morphology, mycelial compatibility, analysis of genomic DNA through random amplified polymorphic DNA (RAPD), variation within the nuclear rDNA [internal transcribed spacers (ITS)] and sequencing of ITS fragments. There was considerable variability among isolates in relation to the number, size and location of sclerotia on the medium surface. Thirteen mycelial compatibility groups (MCG) were identified among 23 isolates. Seven isolates were only self‐compatible. With the exception of group 3, where all the isolates came from soybean, there was no apparent correlation between group and isolate origin. On the basis of RAPD profiles, 11 haplotypes (A to K) were identified. There was an association between the RAPD groups and MCG. Haplotypes A, B, D, G, I and K belonged to MCG groups 1, 2, 3, 4, 5 and 6, respectively. All other RAPD haplotypes contained incompatible isolates. Polymerase chain reaction (PCR) amplification with primers 4R and 5F amplified two fragments containing ITS1, ITS2 and 5.8 S rDNA sequences, that were present in all isolates, with molecular sizes of 739 and 715 bp. Restriction analysis of PCR products showed that the two fragments had sequence divergency which is referred to as ‘ITS types’. Four arbitrarily chosen soybean isolates (2, 6, 7 and 23) and two non‐soybean isolates (11 and 22) were used to investigate the variation within the ITS sequence and its role in the phylogeny. The strict consensus of nine most‐parsimonious trees inferred from the data set which included six isolates of S. rolfsii, four of which have two different ‘ITS types’, showed three well‐supported groupings. The neighbour‐joining tree inferred from the data set also showed three major clades as did the parsimony tree. The major difference was that in the neighbour‐joining tree the ‘ITS type’ 11 was resolved and grouped in one clade. These results show that the ‘ITS types’ within isolates are almost always phylogenetically distinct. There was no clear correlation between ITS‐based phylogeny and isolate origin.     

Electrophoretic protein patterns of three species ofPhytophthora associated with black pod disease of cocoa (Theobroma cacao L.)

When electrophoretic profiles of native proteins from vegetative mycelia ofPhytophthora palmivora, Phytophthora capsici and Phytophthora citrophthora causing black pod disease of cocoa in India were compared on a single Polyacrylamide gel, the isolates of same species were readily distinguished both qualitatively by visual similarity in banding patterns and quantitatively by calculating similarity coefficients. Similarity coefficients were generally much higher between isolates within a species than between isolates of different species. The dendrograms obtained after unweighted pair grouping with arithmetic averaging cluster analysis, revealed that all the isolates ofPhytophthora capsici were highly homogenous and formed a single cluster. The isolates ofPhytophthora citrophthora were resolved into two electrophoretic types which were clustered into two distinct sub groups.Phytophthora palmivora formed a separate group. Thus, the results reveal that polyacrylamide gel electrophoresis can be used successfully in distinguishing species and sub groups within a species ofPhytophthora encountered on cocoa. CPCRl contribution No. 914.     

Phytophthora chrysanthemi sp. nov., a new species causing root rot of chrysanthemum in Japan

A new species of Phytophthora was isolated from stem and root rot of chrysanthemum in the Gifu and Toyama prefectures of Japan. The species differs from other Phytophthora species morphologically, and is characterized by nonpapillate, noncaducous sporangia with internal proliferation, formation of both hyphal swellings and chlamydospores, homothallic nature, distinctive intercalary antheridia, and funnel-shaped oogonia. The new species can grow even at 35°C, with an optimum growth temperature of 30°C in V8 juice agar medium. In phylogenetic analyses based on five nuclear regions (LSU rDNA; genes for translation elongation factor 1α, β-tubulin, 60 S ribosomal protein L10, and heat shock protein 90), the isolates formed a monophyletic clade. Although the rDNA ITS region shows a high resolution and has proven particularly useful for the separation of Phytophthora species, it was difficult to align the sequences for phylogenetic analysis. Therefore, ITS region analysis using related species as defined by the multigene phylogeny was performed, and the topology of the resulting tree also revealed a monophyletic clade formed by the isolates of the species. The morphological characteristics and phylogenetic relationships indicate that the isolates represent a new species, Phytophthora chrysanthemi sp. nov. In pathogenicity tests, chrysanthemum plants inoculated with the isolates developed lesions on stems and roots within 3 days, and the symptoms resembled the ones originally observed. Finally, the pathogen’s identity was confirmed by re-isolation from lesions of infected plants.     

Phytophthora captiosa sp. nov. and P. fallax sp. nov. causing crown dieback of Eucalyptus in New Zealand

A locally severe crown disease of exotic plantation Eucalyptus trees has been recorded periodically in New Zealand since 1986. Symptoms include leaf spots, petiole infection and twig and small branch lesions. Outbreaks of disease are episodic and individual trees may show marked variation in crown symptoms ranging from unaffected to total defoliation. Two previously unknown species of Phytophthora are associated with the disease. These are described and formally designated here as P. captiosa, from Eucalyptus botryoides and E. saligna; and P. fallax, from E. delegatensis, E. fastigata, E. nitens and E. regnans. Both P. captiosa and P. fallax have non-papillate, non-caducous sporangia and both are self-fertile. Phylogenetic analysis on the basis of ITS rDNA sequence data indicates they are closely related to each other but evolutionarily distant from the majority of described Phytophthora taxa. They share a common ancestor with another assemblage of Phytophthora lineages that includes P. insolita, P. macrochlamydospora and P. richardiae. Sporulation of P. captiosa and P. fallax has not been observed in the field. The mode of infection and spread of these non-caducous Phytophthora species in the eucalypt tree canopy remains unknown. This issue, and the possible geographic origins of these two Phytophthora species are discussed.     

Are the polygenic architectures of resistance to <Emphasis Type="Italic">Phytophthora capsici</Emphasis> and <Emphasis Type="Italic">P. parasitica</Emphasis> independent in pepper?

The pepper accession Criollo de Morelos 334 is the most efficient source of resistance currently known to Phytophthora capsici and P. parasitica. To investigate whether genetic controls of resistance to two Phytophthora species are independent, we compared the genetic architecture of resistance of CM334 to both Phytophthora species. The RIL population F5YC used to construct the high-resolution genetic linkage map of pepper was assessed for resistance to one isolate of each Phytophthora species. Inheritance of the P. capsici and P. parasitica resistance was polygenic. Twelve additive QTLs involved in the P. capsici resistance and 14 additive QTLs involved in the P. parasitica resistance were detected. The QTLs identified in this progeny were specific to these Phytophthora species. Comparative mapping analysis with literature data identified three colocations between resistance QTLs to P. parasitica and P. capsici in pepper. Whereas this result suggests presence of common resistance factors to the two Phytophthora species in pepper, which possibly derive from common ancestral genes, calculation of the colocation probability indicates that these colocations could occur by chance.     

A Species-Specific Polymerase Chain Reaction Assay for Rapid and Sensitive Detection of <Emphasis Type="Italic">Colletotrichum</Emphasis><Emphasis Type="Italic">capsici</Emphasis>

Colletotrichum capsici is an important fungal species that causes anthracnose in many genera of plants causing severe economic losses worldwide. A primer set was designed based on the sequences of the ribosomal internal transcribed spacer (ITS1 and ITS2) regions for use in a conventional PCR assay. The primer set (CcapF/CcapR) amplified a single product of 394 bp with DNA extracted from 20 Mexican isolates of C. capsici. The specificity of primers was confirmed by the absence of amplified product with DNA of four other Colletotrichum species and eleven different fungal genera. This primer set is capable of amplifying only C. capsici from different contaminated tissues or fungal structures, thereby facilitating rapid diagnoses as there is no need to isolate and cultivate the fungus in order to identify it. The sensitivity of detection with this PCR method was 10 pg of genomic DNA from the pathogen. This is the first report of a C. capsici-specific primer set. It allows rapid pathogen detection and provides growers with a powerful tool for a rational selection of fungicides to control anthracnose in different crops and in the post-harvest stage.     

Aggressiveness and diversity of Phytophthora capsici on vegetable crops in Georgia

Phytophthora blight induced by Phytophthora capsici causes significant yield loss in a number of vegetable crops. It is imperative to understand the diversity and aggressiveness of the pathogen to design more efficient disease management programs. A collection of P. capsici strains isolated from different vegetable crops in Georgia, USA, were characterised in this study. Of the 49 isolates tested, 24 were A1 and 25 were A2 mating type, respectively, with both mating types found in the same fields. Variability of the isolates was assessed in terms of their aggressiveness on six pepper genotypes. The isolates differed in their aggressiveness on different pepper cultivars with 10 pathotypes identified. No correlation between aggressiveness of the isolates and their host origin or geographical location of isolation was observed. Randomly amplified polymorphic DNA (RAPD) analysis was used to evaluate genetic variability among P. capsici populations. RAPD analysis using 15 random primers resulted in 133 reproducible bands and cluster analysis separated the isolates into 5 groups. Analysis of molecular variance showed that there was moderate genetic differentiation associated with host origin and geographical location of the isolates. No correlation was found between RAPD groups and pathotypes or mating types. These results indicate that P. capsici populations infecting vegetable crops in Georgia were genetically diverse, which should be taken into account in developing resistant cultivars or other disease management programmes.     

Screening Study of Potential Lead Compounds for Natural Product-based Fungicides Against Phytophthora Species

Phytophthora spp. is one of the phytopathogenic Oomycete responsible for many important crop losses. Relevant species are P. infestans (causing potato late blight) and P. capsici (causing blight in pepper). In recent years, the use of conventional fungicides has favoured the appearance of different resistant strains. This study analyses the effect of various compounds on these two Phytophthora species. Those compounds were designed on the basis of known structures of natural compounds to obtain a rational control of these fungal‐like species. All the analysed products showed a fungistatic activity against both strains, one of them reduced mycelial growth by over 46% at 100 p.p.m.     

Survival and recovery of Phytophthora capsici and oomycetes in tailwater and soil from vegetable fields in Florida

A current trend in Florida agriculture to conserve water is to irrigate with surface runoff water (tailwater) recovered in retention ponds and canals. Water filtration and lemon leaf baiting recovered Phytophthora capsici and other plant pathogenic Oomycetes in runoff water from ponds and canals. A total of 196 isolates of Phytophthora spp. and 471 isolates of Pythium spp. were recovered. Phytophthora spp. included P. capsici, P. cinnamomi, P. lateralis, P. nicotianae, P. citricola, P. cryptogea and P. erythroseptica. Species of Pythium were P. aphanidermatum, P. catenulatum, P. helicoides, P. irregulare, P. myriotylum, and Pythium‘group F’. Isolates of P. aphanidermatum, P. irregulare, P. myriotylum, and Pythium‘group F’ were pathogenic on pepper and tomato. Recovery of P. capsici propagules was related to soil moisture‐holding capacity and time interval but not temperature. Recovery of P. capsici propagules at 100% soil moisture‐holding capacity and 30° C was 57 days. In tailwater, recovery of propagules of P. capsici was 63 days at 24°C to 25°C. The potential exists to reintroduce and disseminate species of Phytophthora and Pythium when using tailwater for irrigation or other practices.     

An investigation of biological attributes that may contribute to the importance of Phytophthora capsici as a vegetable pathogen in Florida

During the 1999–2000 and 2000–2001 seasons, 19 commercial squash fields in the vicinity of Homestead, Florida (USA) were examined for diseases caused by Phytophthora capsici. In each of the six fields in which two or more isolates of P. capsici were recovered, both the Al and A2 mating types were present, and both mating types were recovered from the same plant five times. Insensitivity to mefenoxam was common among isolates, with EC50s ranging from 5 μg mefenoxam ml^?1 to more than 60 μg ml^?1. Of 15 weed species that were examined as possible alternative hosts of the pathogen, only common purslane, Portulaca oleracea, was infected by P. capsici. Few or no oospores of the pathogen formed in a glasshouse (c. 28°C) when artificially inoculated pepper plants were covered with plastic bags or kept under continuous mist. In studies in the laboratory (c. 22°C) with detached pepper leaves, no oospores were formed on wire screens over water reservoirs. Consistent production of oospores occurred only when leaves were in constant contact with water. Maximum production occurred at 18°C, and production also occurred at 14°C, 20°C, 24°C and 26°C, but not at 6°C, 12°C, 30°C and 32°C.     

First Report of Phytophthora Foliar Blight on Florida Hopbush (Dodonaea viscosa) in Italy

During 2010, a new foliar blight was detected on potted Dodonaea viscosa cv. Purpurea plants in two nurseries in Catania (Italy). On the basis of morphological and cultural features, the pathogen was identified as Phytophthora palmivora. The internal transcribed spacer (ITS)‐rDNA sequence of a representative Phytophthora isolate from hopbush showed 99% identity with other ITS sequences of different P. palmivora isolates available in GenBank, thus confirming the morpho‐cultural identification. Koch’s postulates were fulfilled by pathogenicity tests on potted D. viscosa cv. Purpurea seedlings. To our knowledge, this is the first report of P. palmivora foliar blight disease on D. viscosa.     

Outbreak of Phytophthora cinnamomi causing severe decline of avocado trees in southern Turkey

Since the summer 2017, severe decline symptoms have been observed on 10- to 25-year-old avocado trees in almost all commercial orchards planted in the Mediterranean coastal region of Turkey. Young, newly planted trees in infected orchards were also affected by the disease. Affected trees showed wilting, leaf discoloration, defoliation and severe dieback. Some trees were completely desiccated. Although fine roots of symptomatic trees usually were decayed, reddish brown cankers also occurred on taproots and lateral roots of heavily infected trees. The pathogens were isolated from necrotic root and soil samples of symptomatic trees, using selective medium and soil baiting, and were identified based on morphological features and DNA sequences of the internal transcribed spacer (ITS) region. One isolate each of Phytophthora cryptogea and P. palmivora was identified, while all other isolates were P. cinnamomi. In addition, a subcortical fan-shaped mycelium, characteristic of Armillaria spp., was observed in the stem base of a symptomatic tree and identified as Armillaria gallica by DNA sequences of the internal transcribed spacer (ITS) and the translational elongation factor 1-α (EF 1-α) gene regions. Pathogenicity of Phytophthora isolates was tested by stem inoculation on one-year-old avocado seedlings. Two months after inoculation, canker lesions developed on stems of seedlings inoculated by any of the three Phytophthora spp. In contrast, collenchyma callus formed over the wound points on control plants over the same time period. This is the first report of P. cinnamomi, P. cryptogea, P. palmivora and A. gallica causing root rot of avocado trees in Turkey. In addition, P. cryptogea and A. gallica are reported for the first time associated with disease on this host. Due to the severe symptoms and widespread occurrence, P. cinnamomi should be considered a potential threat to avocado cultivation and natural ecosystems of this region of Turkey.     

Phytophthora melonis Associated with Fruit and Vine Rot Disease of Pointed Gourd in India as Revealed by RFLP and Sequencing of ITS Region

Pointed gourd is an important tropical high value vegetable crop, which is mainly affected by fruit and vine rot disease in field conditions. Causal organism of this devastating disease is Phytophthora melonis as revealed through morphological criteria as well as by molecular tools based on the restriction fragment length polymorphism (RFLP) of non‐coding Internal Transcriber Spacer (ITS) region and ITS sequencing. Sequencing of ITS region of our Ph. melonis isolate has 100% similarity with the five isolates of GenBank including a Ph. sinensis. The pathogen, Ph. melonis, is a new report from India and as regards host ranges a possible new report globally.     

Trichoderma from Aceh Sumatra reduce Phytophthora lesions on pods and cacao seedlings

The cocoa tree, Theobroma cacao L., suffers large yield losses in Aceh Indonesia due to the disease black pod rot, caused by Phytophthora spp. Despite having the largest area under cacao production in Sumatra, farmers in the Aceh region have low overall production because of losses to insect pests and black pod rot. Trichoderma spp. were isolated from the roots and leaves of cacao trees and screened as potential biological control agents. Isolates used in the study were Trichoderma asperellum isolates T2 and T4, Trichoderma longibrachiatum isolates T15 and T16, and Trichoderma virens isolates T1 and Tv. T1, T2, T4, and Tv completely colonized and destroyed Phytophthora tropicalis and Phytophthora palmivora mycelium in precolonized plate assays. All six isolates reduced P. tropicalis, but none reduced the growth of P. palmivora in dual plate assays. Phytophthora growth was suppressed on MIN media amended with sterile heat inactivated Trichoderma culture filtrates, with Tv best suppressing growth of both Phytophthora spp. T. virens isolate Tv was the only isolate observed coiling around P. tropicalis mycelium and disrupted the formation of P. palmivora sporangia. Of all six isolates, only Tv reduced P. palmivora lesion expansion in a detached pod assay, reducing severity by 71%. Tv also reduced P. palmivora infection on seedlings when applied aerially at 1 × 10⁶ and 1 × 10⁸ conidia/ml, by 19% and 59%, respectively. T. virens isolate Tv is a mycoparasite, antagonizes Phytophthora in a dual plate assay, and shows antibiosis against Phytophthora spp., suggesting that multiple modes of action contribute to its ability to limit Phytophthora lesion expansion on cacao pods and seedlings.     

Characterization of Alder Phytophthora Isolates from Wallonia and Development of SCAR Primers for their Specific Detection

Isolates of alder Phytophthora were collected in the southern part of Belgium on riverbanks planted with Alnus glutinosa and A. incana. They were compared with strains isolated in other European countries in terms of maximum temperature for growth, oogonia shape, pathogenicity on Alnus seedlings and genetic traits. Using both molecular techniques [random amplified polymorphic DNA (RAPD) and random amplified microsatellite (RAMS)], two groups of isolates were identified, the first group being further divided into two subgroups, Ia and Ib, using RAPD. Most of the Walloon alder Phytophthora isolates as well as the standard type from UK (formally designated P. alni subsp. alni) fell into group Ia. One isolate was classified in group Ib with the German and Dutch variants (P. alni subsp. multiformis), while three isolates were placed with the Swedish variant (P. alni subsp. uniformis) in group II. In terms of morphological properties, isolates from groups Ia and Ib developed colonies with a felt‐like appearance and usually produced numerous oogonia, varying from wavy to warty after 1 week (group Ia) or 2–3 weeks (Ib) in darkness. In contrast, colonies from group II isolates were generally irregular, and smooth oogonia were produced in low quantities after approximately 1 month in culture. A polymerase chain reaction (PCR) using sequence‐characterized amplification region (SCAR) primers derived from a polymorphic amplification product generated with a RAPD primer was developed for the specific detection of alder Phytophthora. The specificity and sensitivity of this test are discussed here.     

Rapid detection of Phytophthora nicotianae by simple DNA extraction and real‐time loop‐mediated isothermal amplification assay

Phytophthora nicotianae is a phytopathogenic oomycete with a wide host range and worldwide distribution. Rapid detection and diagnosis at the early stages of disease development are important for the effective control of P. nicotianae. In this study, we designed a simple and rapid loop‐mediated isothermal amplification (LAMP)‐based detection method for P. nicotianae. We tested three DNA extraction methods and selected the Kaneka Easy DNA Extraction Kit version 2, which is rapid and robust for LAMP‐based detection. The designed primers were tested using mycelial DNA from 35 species (81 isolates) of Phytophthora, 12 species (12 isolates) of Pythium, one isolate of Phytopythium and one isolate each from seven other soil‐borne pathogens. All of the 42 P. nicotianae isolates were detected by these primers, and no other isolates gave positive results. Three isolates were tested for the sensitivity of the reaction, and the lowest amounts of template DNA that could be detected were 10 fg for two isolates and 1 fg for the third. The target was detected within 25 min in all tested samples, including DNA extracted from both inoculated and naturally infected plants. In contrast, PCR assays with P. nicotianae‐specific primers failed or showed weakened detection in several samples. Thus, we found that the rapid DNA extraction and LAMP assay methods developed in this study can be used to detect P. nicotianae with high sensitivity, specificity and stability.