Chamomile Floricolous Downy Mildew Caused by Peronospora radii.

Floricolous downy mildews (Peronospora, oomycetes) are a small, monophyletic group of mostly inconspicuous plant pathogens that induce symptoms exclusively on flowers. Characterization of this group of pathogens, and information about their biology, is particularly sparse. The recurrent presence of a disease causing flower malformation which, in turn, leads to high production losses of the medicinal herb Matricaria chamomilla in Serbia has enabled continuous experiments focusing on the pathogen and its biology. Peronospora radii was identified as the causal agent of the disease, and morphologically and molecularly characterized. Diseased chamomile flowers showed severe malformations of the disc and ray florets, including phyllody and secondary inflorescence formation, followed by the onset of downy mildew. Phylogeny, based on internal transcribed spacer and cox2, indicates clustering of the Serbian P. radii with other P. radii from chamomile although, in cox2 analyses, they formed a separate subcluster. Evidence pointing to systemic infection was provided through histological and molecular analyses, with related experiments validating the impact of soilborne and blossom infections. This study provides new findings in the biology of P. radii on chamomile, thus enabling the reconstruction of this floricolous Peronospora species' life cycle.

A secreted WY-domain-containing protein present in European isolates of the oomycete Plasmopara viticola induces cell death in grapevine and tobacco species.

Plasmopara viticola is a biotrophic oomycete pathogen causing grapevine downy mildew. We characterized the repertoire of P. viticola effector proteins which may be translocated into plants to support the disease. We found several secreted proteins that contain canonical dEER motifs and conserved WY-domains but lack the characteristic RXLR motif reported previously from oomycete effectors. We cloned four candidates and showed that one of them, Pv33, induces plant cell death in grapevine and Nicotiana species. This activity is dependent on the nuclear localization of the protein. Sequence similar effectors were present in seven European, but in none of the tested American isolates. Together our work contributes a new type of conserved P. viticola effector candidates.

Advances in Diagnostics of Downy Mildews: Lessons Learned from Other Oomycetes and Future Challenges.

Downy mildews are plant pathogens that damage crop quality and yield worldwide. Among the most severe and notorious crop epidemics of downy mildew occurred on grapes in the mid-1880s, which almost destroyed the wine industry in France. Since then, there have been multiple outbreaks on sorghum and millet in Africa, tobacco in Europe, and recent widespread epidemics on lettuce, basil, cucurbits, and spinach throughout North America. In the mid-1970s, loss of corn to downy mildew in the Philippines was estimated at US$23 million. Today, crops that are susceptible to downy mildews are worth at least $7.5 billion of the United States' economy. Although downy mildews cause devastating economic losses in the United States and globally, this pathogen group remains understudied because they are difficult to culture and accurately identify. Early detection of downy mildews in the environment is critical to establish pathogen presence and identity, determine fungicide resistance, and understand how pathogen populations disperse. Knowing when and where pathogens emerge is also important for identifying critical control points to restrict movement and to contain populations. Reducing the spread of pathogens also decreases the likelihood of sexual recombination events and discourages the emergence of novel virulent strains. A major challenge in detecting downy mildews is that they are obligate pathogens and thus cannot be cultured in artificial media to identify and maintain specimens. However, advances in molecular detection techniques hold promise for rapid and in some cases, relatively inexpensive diagnosis. In this article, we discuss recent advances in diagnostic tools that can be used to detect downy mildews. First, we briefly describe downy mildew taxonomy and genetic loci used for detection. Next, we review issues encountered when identifying loci and compare various traditional and novel platforms for diagnostics. We discuss diagnosis of downy mildew traits and issues to consider when detecting this group of organisms in different environments. We conclude with challenges and future directions for successful downy mildew detection.

Multiple gene genealogy reveals high genetic diversity and evidence for multiple origins of Chinese Plasmopara viticola population.

Downy mildew caused by Plasmopara viticola is one of the most devastating diseases of grapevines worldwide. So far, the genetic diversity and origin of the Chinese P. viticola population are unclear. In the present study, 103 P. viticola isolates were sequenced at four gene regions: internal transcribed spacer one (ITS), large subunit of ribosomal RNA (LSU), actin gene (ACT) and beta-tubulin (TUB). The sequences were analyzed to obtain polymorphism and diversity information of the Chinese population as well as to infer the relationships between Chinese and American isolates. High genetic diversity was observed for the Chinese population, with evidence of sub-structuring based on climate. Phylogenetic analysis and haplotype networks showed evidence of close relationships between some American and Chinese isolates, consistent with recent introduction from America to China via planting materials. However, there is also evidence for endemic Chinese P. viticola isolates. Our results suggest that the current Chinese Plasmopara viticola population is an admixture of endemic and introduced isolates.

First report of Leptolegnia chapmanii (Peronosporomycetes: Saprolegniales) affecting mosquitoes in central Brazil.

Numerous isolates of an oomycete 'fungus', Leptolegnia chapmanii, are reported from Brazil for the first time. This aquatic pathogen was baited with Aedes aegypti sentinel larvae from stagnant, temporary bodies of water in selected locations under secondary tropical forest in and near the central Brazilian city of Goiânia and from more distant sites in the western and northern regions of the state of Goiás. Isolates were identified based on their morphological and developmental characters, comparative sequence data for the ITS and TEF loci, as well as their rapid activity against A. aegypti larvae. Taxonomic issues affecting the application of the name L. chapmanii and its typification are rectified. This study contributes to a better understanding of the presence and distribution of this oomycete in Brazil, its sequence-based identification, and of its potential as a biological agent against mosquito vectors.

Genome Sequence and Architecture of the Tobacco Downy Mildew Pathogen Peronospora tabacina.

Peronospora tabacina is an obligate biotrophic oomycete that causes blue mold or downy mildew on tobacco (Nicotiana tabacum). It is an economically important disease occurring frequently in tobacco-growing regions worldwide. We sequenced and characterized the genomes of two P. tabacina isolates and mined them for pathogenicity-related proteins and effector-encoding genes. De novo assembly of the genomes using Illumina reads resulted in 4,016 (63.1 Mb, N50 = 79 kb) and 3,245 (55.3 Mb, N50 = 61 kb) scaffolds for isolates 968-J2 and 968-S26, respectively, with an estimated genome size of 68 Mb. The mitochondrial genome has a similar size (approximately 43 kb) and structure to those of other oomycetes, plus several minor unique features. Repetitive elements, primarily retrotransposons, make up approximately 24% of the nuclear genome. Approximately 18,000 protein-coding gene models were predicted. Mining the secretome revealed approximately 120 candidate RxLR, six CRN (candidate effectors that elicit crinkling and necrosis), and 61 WY domain-containing proteins. Candidate RxLR effectors were shown to be predominantly undergoing diversifying selection, with approximately 57% located in variable gene-sparse regions of the genome. Aligning the P. tabacina genome to Hyaloperonospora arabidopsidis and Phytophthora spp. revealed a high level of synteny. Blocks of synteny show gene inversions and instances of expansion in intergenic regions. Extensive rearrangements of the gene-rich genomic regions do not appear to have occurred during the evolution of these highly variable pathogens. These assemblies provide the basis for studies of virulence in this and other downy mildew pathogens.

Multi-locus tree and species tree approaches toward resolving a complex clade of downy mildews (Straminipila, Oomycota), including pathogens of beet and spinach.

Accurate species determination of plant pathogens is a prerequisite for their control and quarantine, and further for assessing their potential threat to crops. The family Peronosporaceae (Straminipila; Oomycota) consists of obligate biotrophic pathogens that cause downy mildew disease on angiosperms, including a large number of cultivated plants. In the largest downy mildew genus Peronospora, a phylogenetically complex clade includes the economically important downy mildew pathogens of spinach and beet, as well as the type species of the genus Peronospora. To resolve this complex clade at the species level and to infer evolutionary relationships among them, we used multi-locus phylogenetic analysis and species tree estimation. Both approaches discriminated all nine currently accepted species and revealed four previously unrecognized lineages, which are specific to a host genus or species. This is in line with a narrow species concept, i.e. that a downy mildew species is associated with only a particular host plant genus or species. Instead of applying the dubious name Peronospora farinosa, which has been proposed for formal rejection, our results provide strong evidence that Peronospora schachtii is an independent species from lineages on Atriplex and apparently occurs exclusively on Beta vulgaris. The members of the clade investigated, the Peronospora rumicis clade, associate with three different host plant families, Amaranthaceae, Caryophyllaceae, and Polygonaceae, suggesting that they may have speciated following at least two recent inter-family host shifts, rather than contemporary cospeciation with the host plants.

Coupling Spore Traps and Quantitative PCR Assays for Detection of the Downy Mildew Pathogens of Spinach (Peronospora effusa) and Beet (P. schachtii).

Downy mildew of spinach (Spinacia oleracea), caused by Peronospora effusa, is a production constraint on production worldwide, including in California, where the majority of U.S. spinach is grown. The aim of this study was to develop a real-time quantitative polymerase chain reaction (qPCR) assay for detection of airborne inoculum of P. effusa in California. Among oomycete ribosomal DNA (rDNA) sequences examined for assay development, the highest nucleotide sequence identity was observed between rDNA sequences of P. effusa and P. schachtii, the cause of downy mildew on sugar beet and Swiss chard in the leaf beet group (Beta vulgaris subsp. vulgaris). Single-nucleotide polymorphisms were detected between P. effusa and P. schachtii in the 18S rDNA regions for design of P. effusa- and P. schachtii-specific TaqMan probes and reverse primers. An allele-specific probe and primer amplification method was applied to determine the frequency of both P. effusa and P. schachtii rDNA target sequences in pooled DNA samples, enabling quantification of rDNA of P. effusa from impaction spore trap samples collected from spinach production fields. The rDNA copy numbers of P. effusa were, on average, ≈3,300-fold higher from trap samples collected near an infected field compared with those levels recorded at a site without a nearby spinach field. In combination with disease-conducive weather forecasting, application of the assays may be helpful to time fungicide applications for disease management.

Geographic distribution of cryptic species of Plasmopara viticola causing downy mildew on wild and cultivated grape in eastern North America.

The putative center of origin of Plasmopara viticola, the causal agent of grape downy mildew, is eastern North America, where it has been described on several members of the family Vitaceae (e.g., Vitis spp., Parthenocissus spp., and Ampelopsis spp.). We have completed the first large-scale sampling of P. viticola isolates across a range of wild and cultivated host species distributed throughout the above region. Sequencing results of four partial genes indicated the presence of a new P. viticola species on Vitis vulpina in Virginia, adding to the four cryptic species of P. viticola recently recorded. The phylogenetic analysis also indicated that the P. viticola species found on Parthenocissus quinquefolia in North America is identical to Plasmopara muralis in Europe. The geographic distribution and host range of five pathogen species was determined through analysis of the internal transcribed spacer polymorphism of 896 isolates of P. viticola. Among three P. viticola species found on cultivated grape, one was restricted to Vitis interspecific hybrids within the northern part of eastern North America. A second species was recovered from V. vinifera and V. labrusca, and was distributed across most of the sampled region. A third species, although less abundant, was distributed across a larger geographical range, including the southern part of eastern North America. P. viticola clade aestivalis predominated (83% of isolates) in vineyards of the European winegrape V. vinifera within the sampled area, indicating that a single pathogen species may represent the primary threat to the European host species within eastern North America.

Disentangling Peronospora on Papaver: phylogenetics, taxonomy, nomenclature and host range of downy mildew of opium poppy (Papaver somniferum) and related species.

Based on sequence data from ITS rDNA, cox1 and cox2, six Peronospora species are recognised as phylogenetically distinct on various Papaver species. The host ranges of the four already described species P. arborescens, P. argemones, P. cristata and P. meconopsidis are clarified. Based on sequence data and morphology, two new species, P. apula and P. somniferi, are described from Papaver apulum and P. somniferum, respectively. The second Peronospora species parasitizing Papaver somniferum, that was only recently recorded as Peronospora cristata from Tasmania, is shown to represent a distinct taxon, P. meconopsidis, originally described from Meconopsis cambrica. It is shown that P. meconopsidis on Papaver somniferum is also present and widespread in Europe and Asia, but has been overlooked due to confusion with P. somniferi and due to less prominent, localized disease symptoms. Oospores are reported for the first time for P. meconopsidis from Asian collections on Papaver somniferum. Morphological descriptions, illustrations and a key are provided for all described Peronospora species on Papaver. cox1 and cox2 sequence data are confirmed as equally good barcoding loci for reliable Peronospora species identification, whereas ITS rDNA does sometimes not resolve species boundaries. Molecular phylogenetic data reveal high host specificity of Peronospora on Papaver, which has the important phytopathological implication that wild Papaver spp. cannot play any role as primary inoculum source for downy mildew epidemics in cultivated opium poppy crops.

Molecular detection of Peronospora variabilis in quinoa seed and phylogeny of the quinoa downy mildew pathogen in South America and the United States.

Quinoa (Chenopodium quinoa) is an important export of the Andean region, and its key disease is quinoa downy mildew, caused by Peronospora variabilis. P. variabilis oospores can be seedborne and rapid methods to detect seedborne P. variabilis have not been developed. In this research, a polymerase chain reaction (PCR)-based detection method was developed to detect seedborne P. variabilis and a sequencing-based method was used to validate the PCR-based method. P. variabilis was detected in 31 of 33 quinoa seed lots using the PCR-based method and in 32 of 33 quinoa seed lots using the sequencing-based method. Thirty-one of the quinoa seed lots tested in this study were sold for human consumption, with seed originating from six different countries. Internal transcribed spacer (ITS) and cytochrome c oxidase subunit 2 (COX2) phylogenies were examined to determine whether geographical differences occurred in P. variabilis populations originating from Ecuador, Bolivia, and the United States. No geographical differences were observed in the ITS-derived phylogeny but the COX2 phylogeny indicated that geographical differences existed between U.S. and South American samples. Both ITS and COX2 phylogenies supported the existence of a Peronospora sp., distinct from P. variabilis, that causes systemic-like downy mildew symptoms on quinoa in Ecuador. The results of these studies allow for a better understanding of P. variabilis populations in South America and identified a new causal agent for quinoa downy mildew. The PCR-based seed detection method allows for the development of P. variabilis-free quinoa seed, which may prove important for management of quinoa downy mildew.

Mitochondrial phylogeny reveals intraspecific variation in Peronospora effusa, the spinach downy mildew pathogen.

Since about two hundred years, downy mildew caused by Peronospora effusa is probably the most economically important disease of spinach (Spinacia oleracea). However, there is no information on the global phylogeographic structure of the pathogen and thus it is unclear whether a single genotype occurs worldwide or whether some local genetic variation exists. To investigate the genetic variability of this pathogen, a sequence analysis of two partial mitochondrial DNA genes, cox2 and nad1, was carried out. Thirty-three specimens of Peronospora effusa from four continents were analyzed, including samples from Australia, China, Japan, Korea, Mexico, Russia, Sweden, and the USA. Despite the potential anthropogenic admixture of genotypes, a phylogeographic pattern was observed, which corresponds to two major groups, an Asian/Oceanian clade and another group, which includes American/European specimens. Notably, two of six Japanese specimens investigated did not belong to the Asian/Oceanian clade, but were identical to three of the specimens from the USA, suggestive of a recent introduction from the USA to Japan. As similar introduction events may be occurring as a result of the globalised trade with plant and seed material, a better knowledge of the phylogeographic distribution of pathogens is highly warranted for food security purposes.

Characterization of single-nucleotide-polymorphism markers for Plasmopara viticola, the causal agent of grapevine downy mildew.

We report 34 new nuclear single-nucleotide-polymorphism (SNP) markers that have been developed from an expressed sequence tag library of Plasmopara viticola, the causal agent of grapevine downy mildew. This newly developed battery of markers will provide useful additional genetic tools for population genetic studies of this important agronomic species.

The cucurbit downy mildew pathogen Pseudoperonospora cubensis.

Pseudoperonospora cubensis[(Berkeley & M. A. Curtis) Rostovzev], the causal agent of cucurbit downy mildew, is responsible for devastating losses worldwide of cucumber, cantaloupe, pumpkin, watermelon and squash. Although downy mildew has been a major issue in Europe since the mid-1980s, in the USA, downy mildew on cucumber has been successfully controlled for many years through host resistance. However, since the 2004 growing season, host resistance has been effective no longer and, as a result, the control of downy mildew on cucurbits now requires an intensive fungicide programme. Chemical control is not always feasible because of the high costs associated with fungicides and their application. Moreover, the presence of pathogen populations resistant to commonly used fungicides limits the long-term viability of chemical control. This review summarizes the current knowledge of taxonomy, disease development, virulence, pathogenicity and control of Ps. cubensis. In addition, topics for future research that aim to develop both short- and long-term control measures of cucurbit downy mildew are discussed. TAXONOMY: Kingdom Straminipila; Phylum Oomycota; Class Oomycetes; Order Peronosporales; Family Peronosporaceae; Genus Pseudoperonospora; Species Pseudoperonospora cubensis. DISEASE SYMPTOMS: Angular chlorotic lesions bound by leaf veins on the foliage of cucumber. Symptoms vary on different cucurbit species and varieties, specifically in terms of lesion development, shape and size. Infection of cucurbits by Ps. cubensis impacts fruit yield and overall plant health. INFECTION PROCESS: Sporulation on the underside of leaves results in the production of sporangia that are dispersed by wind. On arrival on a susceptible host, sporangia germinate in free water on the leaf surface, producing biflagellate zoospores that swim to and encyst on stomata, where they form germ tubes. An appressorium is produced and forms a penetration hypha, which enters the leaf tissue through the stomata. Hyphae grow through the mesophyll and establish haustoria, specialized structures for the transfer of nutrients and signals between host and pathogen. CONTROL: Management of downy mildew in Europe requires the use of tolerant cucurbit cultivars in conjunction with fungicide applications. In the USA, an aggressive fungicide programme, with sprays every 5-7 days for cucumber and every 7-10 days for other cucurbits, has been necessary to control outbreaks and to prevent crop loss. USEFUL WEBSITES: http://www.daylab.plp.msu.edu/pseudoperonospora-cubensis/ (Day Laboratory website with research advances in downy mildew); http://veggies.msu.edu/ (Hausbeck Laboratory website with downy mildew news for growers); http://cdm.ipmpipe.org/ (Cucurbit downy mildew forecasting homepage); http://ipm.msu.edu/downymildew.htm (Downy mildew information for Michigan's vegetable growers).

Reclassification of two peronospora species parasitic on draba in hyaloperonospora based on morphological and molecular phylogenetic data.

On the family Brassicaceae, the causal agent responsible for downy mildew disease was originally regarded as a single species, Peronospora parasitica (now under Hyaloperonospora), but it was recently reconsidered to consist of many distinct species. In this study, 11 specimens of Peronospora drabae and P. norvegica parasitic on the genus Draba were investigated morphologically and molecularly. Pronounced differences in conidial sizes (P. drabae: 14-20 × 12.5-15.5 µm; P. norvegica: 20-29 × 15.5-22 µm) and 7.8% sequence distance between their ITS1-5.8S-ITS2 rDNA sequences confirmed their status as distinct species. Based on ITS phylogeny and morphology (monopodially branching conidiophores, flexuous to sigmoid ultimate branchlets, hyaline conidia and lobate haustoria), the two species unequivocally belong to the genus Hyaloperonospora and not to Peronospora to which they were previously assigned. Therefore, two new combinations, Hyaloperonospora drabae and H. norvegica, are proposed. The two taxa are illustrated and compared using the type specimen for H. norvegica and authentic specimens for H. drabae, which is lectotypified.

Universally Primed-PCR indicates geographical variation of Peronospora farinosa ex. Chenopodium quinoa.

In the Andean region of South America downy mildew, caused by Peronospora farinosa, is the most important disease of quinoa (Chenopodium quinoa). Peronospora farinosa, a highly polyphyletic species, occurs on quinoa and wild relatives on all continents. However, very little is known about the geographic diversity of the pathogen. As the interest in quinoa as a novel crop is increasing worldwide, geographical differences in the population structure of the downy mildew pathogen must be taken into consideration in order to design appropriate control strategies under a variety of circumstances. As a step towards understanding the geographic diversity of P. farinosa from quinoa, 40 downy mildew isolates from the Andean highlands and Denmark were characterized using universally primed PCR (UP-PCR). Eight UP-PCR primers were tested. A combined analysis of markers separated the Danish and Andean isolates in two distinct clusters. This study raises new questions about the origin and spread of P. farinosa on quinoa, its geographic diversity and host specificity.

Morphological and molecular characterization of the causal agent of downy mildew on Quinoa (Chenopodium quinoa).

Downy mildew is an economically important and widespread disease in quinoa (Chenopodium quinoa) growing areas. Although in many studies Peronospora farinosa is most commonly regarded as the causal agent of the disease, identification and classification of the pathogen remain still uncertain due to its taxonomic confusion. Thirty-six Peronospora isolates from quinoa with different geographic origins including Argentina, Bolivia, Denmark, Ecuador, and Peru were morphologically and molecularly compared with Peronospora species from other Chenopodium species. The morphology of three herbarium specimens was similar to that of P. variabilis, which originated from C. album, characterized by flexuous to curved ultimate branchlets and pedicellated conidia. Phylogenetic analysis based on ITS rDNA sequences also placed the quinoa pathogen within the same clade as P. variabilis. Within the ITS rDNA sequences of the quinoa pathogens, two base substitutions were found, which separated the majority of the Danish isolates from isolates from South America, but no sequence difference was found among the isolates from different cultivars of quinoa. The present results indicate that the pathogen responsible for the quinoa downy mildew is identical to Peronospora variabilis and that it should not be lumped with P. farinosa as claimed previously by most studies.

Two novel Peronospora species are associated with recent reports of downy mildew on sages.

Recently, downy mildew of Salvia species became economically relevant globally, but the taxonomy of the causal agent remains still obscure. The objective of this study was to characterize and distinguish the different Peronospora species associated with downy mildew on sages, based on morphological and molecular data. For this purpose we compared Peronospora specimens on Salvia officinalis and Salvia plebeia with Peronospora swinglei, including the type specimen on Salvia reflexa. We observed that three Peronospora species are associated with downy mildew on sages, and the recent outbreak of the disease on S. officinalis and S. plebeia is associated with two undescribed species, contrasting the view that either P. swinglei or Peronospora lamii is the causal agent of the downy mildew disease as claimed previously by several studies. In the study presented here, we provide the formal descriptions and illustrations for the two newly introduced taxa, Peronospora salviae-plebeiae and Peronospora salviae-officinalis. The three species of Peronospora investigated seem to be restricted to specific species of Salvia: P. swinglei to S. reflexa, P. salviae-plebeiae to S. plebeia, and P. salviae-officinalis to S. officinalis. Speciation may be allopatric and closely linked to the geographic distributions of their host plants.

Molecular taxonomy of phytopathogenic fungi: a case study in Peronospora.

BACKGROUND: Inappropriate taxon definitions may have severe consequences in many areas. For instance, biologically sensible species delimitation of plant pathogens is crucial for measures such as plant protection or biological control and for comparative studies involving model organisms. However, delimiting species is challenging in the case of organisms for which often only molecular data are available, such as prokaryotes, fungi, and many unicellular eukaryotes. Even in the case of organisms with well-established morphological characteristics, molecular taxonomy is often necessary to emend current taxonomic concepts and to analyze DNA sequences directly sampled from the environment. Typically, for this purpose clustering approaches to delineate molecular operational taxonomic units have been applied using arbitrary choices regarding the distance threshold values, and the clustering algorithms. METHODOLOGY: Here, we report on a clustering optimization method to establish a molecular taxonomy of Peronospora based on ITS nrDNA sequences. Peronospora is the largest genus within the downy mildews, which are obligate parasites of higher plants, and includes various economically important pathogens. The method determines the distance function and clustering setting that result in an optimal agreement with selected reference data. Optimization was based on both taxonomy-based and host-based reference information, yielding the same outcome. Resampling and permutation methods indicate that the method is robust regarding taxon sampling and errors in the reference data. Tests with newly obtained ITS sequences demonstrate the use of the re-classified dataset in molecular identification of downy mildews. CONCLUSIONS: A corrected taxonomy is provided for all Peronospora ITS sequences contained in public databases. Clustering optimization appears to be broadly applicable in automated, sequence-based taxonomy. The method connects traditional and modern taxonomic disciplines by specifically addressing the issue of how to optimally account for both traditional species concepts and genetic divergence.

Identity of the downy mildew pathogens of basil, coleus, and sage with implications for quarantine measures.

The downy mildew pathogen of basil (Ocimum spp.) has caused considerable damage throughout the past five years, and an end to the epidemics is not in sight. The downy mildew of coleus (Solenostemon spp.) is just emerging and here we report that it was very recently introduced into Germany. Although it has been recognised that these pathogens are a major threat, the identity of the pathogens is still unresolved, and so it is difficult to devise quarantine measures against them. Using morphological comparison and molecular phylogenetic reconstructions we confirmed in this study that the downy mildews of basil and coleus are unrelated to Peronospora lamii, which is a common pathogen of the weed Lamium purpureum. In addition, we conclude by the investigation of the type specimen of P. swingleii and downy mildew specimens on Salvia officinalis that the newly occurring pathogens are not identical to P. swingleii on Salvia reflexa. The taxonomy of the downy mildew pathogens of hosts from the Lamiaceae and, in particular, from the tribes Mentheae and Elsholtzieae, is discussed, and a new species is described to accommodate the downy mildew pathogen of basil and coleus, which is the first downy mildew pathogen known to be parasitic to hosts of the tribe Ocimeae.