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In late summer 2022 and 2023, powdery mildew symptoms were found on female plants of hemp (Cannabis sativa) growing in a private garden in Hradec nad Moravicí (Silesia, Czech Republic). On the upper sides of the leaves, white powdery colonies were observed which coalesced and finally covered the whole leaf surface. The stems and flowers were not affected. Microscopic examination revealed the formation of asexual (anamorphic) states characterized by conidiophores forming catenescent conidia (Euoidium type), but with two types of conidia, viz., ellipsoid to ovoid or doliiform conidia with fibrosin bodies (resembling conidia of Podosphaera spp.), and ellipsoid to doliiform conidia without fibrosin bodies (resembling conidia of Golovinomyces spp.). Molecular genetic analyses confirmed co‐infections in the studied hemp samples by two powdery mildew species, viz., Podosphaera macularis and Golovinomyces ambrosiae, which represent first records from the Czech Republic, as well as Europe and in the world. The authors discuss the latest information and ideas regarding this pathosystem. [ABSTRACT FROM AUTHOR]

BackgroundDowny mildews are the most speciose group of oomycetes and affect crops of great economic importance. So far, there is only a single deeply-sequenced downy mildew genome available, from Hyaloperonospora arabidopsidis. Further genomic resources for downy mildews are required to study their evolution, including pathogenicity effector proteins, such as RxLR effectors. Plasmopara halstedii is a devastating pathogen of sunflower and a potential pathosystem model to study downy mildews, as several Avr-genes and R-genes have been predicted and unlike Arabidopsis downy mildew, large quantities of almost contamination-free material can be obtained easily.ResultsHere a high-quality draft genome of Plasmopara halstedii is reported and analysed with respect to various aspects, including genome organisation, secondary metabolism, effector proteins and comparative genomics with other sequenced oomycetes. Interestingly, the present analyses revealed further variation of the RxLR motif, suggesting an important role of the conservation of the dEER-motif. Orthology analyses revealed the conservation of 28 RxLR-like core effectors among Phytophthora species. Only six putative RxLR-like effectors were shared by the two sequenced downy mildews, highlighting the fast and largely independent evolution of two of the three major downy mildew lineages. This is seemingly supported by phylogenomic results, in which downy mildews did not appear to be monophyletic.ConclusionsThe genome resource will be useful for developing markers for monitoring the pathogen population and might provide the basis for new approaches to fight Phytophthora and downy mildew pathogens by targeting core pathogenicity effectors.

Plasmopara halstedii is a biotrophic parasite of sunflower (Helianthus annuus). We genetically analysed 162 P. halstedii samples collected between 1982 and 2018, representing a 3500 km west–east transect across Europe, from France to the Krasnodar region in southern Russia. To assess the population genetic structure among P. halstedii isolates, we sequenced two mitochondrial regions (cox1 and cox2), in addition to analysing eight polymorphic simple sequence repeat (SSR, microsatellite) markers. Sequencing of cox2 enabled comparison of our data with recent SSR‐based studies to provide further evidence for differences among P. halstedii strains infecting different hosts (H. annuus, H. × laetiflorus, Rudbeckia spp.). There are two different lineages infecting H. annuus that we resolved on a neighbour‐joining tree, which also corresponded to a discriminant analysis of principal components. This suggests at least two independent introductions of P. halstedii on sunflower. We observed no relationship between the phylogenetic placement of the individual samples and virulence characteristics, indicating independent evolution of virulence phenotypes. Both genetic markers clearly separated P. halstedii samples originating from H. annuus and H. × laetiflorus, suggesting these might represent distinct species. [ABSTRACT FROM AUTHOR]

Powdery mildews on the Asteraceae family were surveyed during 2007-2015 in the Czech Republic with the aim to increase our knowledge about occurrence, morphological characteristics and host specificity of powdery mildews on this family. In total, 32 host species with symptoms of powdery mildew were collected, and the fungal species were identified based on microscopic observations. These showed great variability in their morphological characteristics. Our study confirmed the high host specificity of powdery mildew species to their original hosts. A deeper knowledge of the taxonomy of the Asteraceae has brought substantial changes in the delimitation of powdery mildew species. In particular, delimitation of the three varieties of Golovinomyces asterum was studied and discussed. [ABSTRACT FROM AUTHOR]