The Effector Repertoire of the Hop Downy Mildew Pathogen Pseudoperonospora humuli

Abstract A description is provided for Pseudoperonospora humuli. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOST: Humulus lupulus. DISEASE: Downy mildew of hops. The first sign of infection, seen early in the year, is the development of spindly, stunted, shoots with pale, crowded and down-curled, leaves. These are known as 'primary basal spikes' and are shoots with a systemic infection developed from mycelium which has overwintered in the rootstock. The undersurfaces of the leaves of these shoots bear large crops of sporangia which in moist and humid conditions can soon spread the disease in the growing crop. Secondary infections may occur on leaves, growing tips, flowers and cones. On the leaves they are seen either as small discrete spots or larger, more angular, brown areas. The diseased shoots arising from secondary infections and depending upon the position of the infected bud are known as 'terminal' or 'lateral' spikes. They resemble basal spikes in appearance. Infection of the flowers can inhibit cone production. If cones do develop, and become infected, the brown spots and lesions of the fungus can make them unsaleable. GEOGRAPHICAL DISTRIBUTION: CMI Map No. 14, ed. 4, 1976, with the addition of Belorussia, Estonia, India, Kinghizia, Kazakhstan, Latvia, Lithuania, Moldavia, Ukraine and Uzebekistan. TRANSMISSION: Ware (1926) demonstrated the presence of mycelium in diseased rootstocks but its significance in the overwintering of the pathogen was not fully recognized until Coley Smith (1962) showed that the primary basal spikes which develop in spring originate from infected buds on the rootstocks. Oospores, which are often produced in abundance, were at one time thought to be responsible for infection of the shoots in spring but there is no convincing evidence to support this theory.

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NEGATIVE EFFECT OF FUNGICIDES USED IN PRACTICAL HOP PROTECTION AGAINST DOWNY MILDEW (PSEUDOPERONOSPORA HUMULI) ON APHIDOPHAGOUS COCCINELLIDS PROPYLEA QUATUORDECIMPUNCTATA L.

Acta Horticulturae ◽

10.17660/actahortic.2013.1010.12 ◽

2013 ◽

pp. 109-112

Author(s):

J. Vostrel

Keyword(s):

Downy Mildew ◽

Propylea Quatuordecimpunctata ◽

Pseudoperonospora Humuli ◽

Negative Effect

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Analysis of microsatellites from the transcriptome of downy mildew pathogens and their application for characterization of Pseudoperonospora populations

PeerJ ◽

10.7717/peerj.3266 ◽

2017 ◽

Vol 5 ◽

pp. e3266 ◽

Cited By ~ 10

Author(s):

Emma C. Wallace ◽

Lina M. Quesada-Ocampo

Keyword(s):

Downy Mildew ◽

Draft Genome ◽

Model Organism ◽

Genomic Analysis ◽

Population Level ◽

Comparative Genomic ◽

Pathogen Population ◽

Pseudoperonospora Humuli ◽

Hyaloperonospora Arabidopsidis

Downy mildew pathogens affect several economically important crops worldwide but, due to their obligate nature, few genetic resources are available for genomic and population analyses. Draft genomes for emergent downy mildew pathogens such as the oomycete Pseudoperonospora cubensis, causal agent of cucurbit downy mildew, have been published and can be used to perform comparative genomic analysis and develop tools such as microsatellites to characterize pathogen population structure. We used bioinformatics to identify 2,738 microsatellites in the P. cubensis predicted transcriptome and evaluate them for transferability to the hop downy mildew pathogen, Pseudoperonospora humuli, since no draft genome is available for this species. We also compared the microsatellite repertoire of P. cubensis to that of the model organism Hyaloperonospora arabidopsidis, which causes downy mildew in Arabidopsis. Although trends in frequency of motif-type were similar, the percentage of SSRs identified from P. cubensis transcripts differed significantly from H. arabidopsidis. The majority of a subset of microsatellites selected for laboratory validation (92%) produced a product in P. cubensis isolates, and 83 microsatellites demonstrated transferability to P. humuli. Eleven microsatellites were found to be polymorphic and consistently amplified in P. cubensis isolates. Analysis of Pseudoperonospora isolates from diverse hosts and locations revealed higher diversity in P. cubensis compared to P. humuli isolates. These microsatellites will be useful in efforts to better understand relationships within Pseudoperonospora species and P. cubensis on a population level.

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Genome Sequencing and Transcriptome Analysis of the Hop Downy Mildew Pathogen Pseudoperonospora humuli Reveal Species-Specific Genes for Molecular Detection

Phytopathology ◽

10.1094/phyto-11-18-0431-r ◽

2019 ◽

Vol 109 (8) ◽

pp. 1354-1366 ◽

Cited By ~ 9

Author(s):

A. Rahman ◽

E. Góngora-Castillo ◽

M. J. Bowman ◽

K. L. Childs ◽

D. H. Gent ◽

...

Keyword(s):

Downy Mildew ◽

Cultural Practices ◽

Disease Risk ◽

Systemic Infection ◽

Primary Methods ◽

Bioinformatics Analyses ◽

Fungicide Application ◽

Pseudoperonospora Humuli ◽

Species Specific ◽

Propagation Material

Pseudoperonospora humuli is an obligate oomycete pathogen of hop (Humulus lupulus) that causes downy mildew, an important disease in most production regions in the Northern Hemisphere. The pathogen can cause a systemic infection in hop, overwinter in the root system, and infect propagation material. Substantial yield loss may occur owing to P. humuli infection of strobiles (seed cones), shoots, and cone-bearing branches. Fungicide application and cultural practices are the primary methods to manage hop downy mildew. However, effective, sustainable, and cost-effective management of downy mildew can be improved by developing early detection systems to inform on disease risk and timely fungicide application. However, no species-specific diagnostic assays or genomic resources are available for P. humuli. The genome of the P. humuli OR502AA isolate was partially sequenced using Illumina technology and assembled with ABySS. The assembly had a minimum scaffold length of 500 bp and an N50 (median scaffold length of the assembled genome) of 19.2 kbp. A total number of 18,656 genes were identified using MAKER standard gene predictions. Additionally, transcriptome assemblies were generated using RNA-seq and Trinity for seven additional P. humuli isolates. Bioinformatics analyses of next generation sequencing reads of P. humuli and P. cubensis (a closely related sister species) identified 242 candidate species-specific P. humuli genes that could be used as diagnostic molecular markers. These candidate genes were validated using polymerase chain reaction against a diverse collection of isolates from P. humuli, P. cubensis, and other oomycetes. Overall, four diagnostic markers were found to be uniquely present in P. humuli. These candidate markers identified through comparative genomics can be used for pathogen diagnostics in propagation material, such as rhizomes and vegetative cuttings, or adapted for biosurveillance of airborne sporangia, an important source of inoculum in hop downy mildew epidemics.

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Peronospora dianthicola. [Descriptions of Fungi and Bacteria].

IMI Descriptions of Fungi and Bacteria ◽

10.1079/dfb/20056400764 ◽

1983 ◽

Author(s):

S. M. Francis

Keyword(s):

Downy Mildew ◽

Geographical Distribution ◽

Disease Transmission ◽

Dianthus Caryophyllus ◽

Weather Conditions ◽

Axillary Buds ◽

Pseudoperonospora Humuli ◽

Resistant Varieties ◽

Weed Hosts ◽

Pale Green

Abstract A description is provided for Peronospora dianthicola. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOST: Dianthus caryophyllus. DISEASE: Downy mildew of carnation. Early symptoms are seen on the leaves which have pale green to yellowish transverse bands and may bend at these lesions. Infected plants are stunted and become withered. Infection of the growing point may result in the development of axillary buds giving the plants a bushy appearance. Barthelet describes the shoots which can develop in some resistant varieties as resembling the basal spikes of Pseudoperonospora humuli on hops, i.e., shoots with smaller leaves, thickened stem and shortened internodes. GEOGRAPHICAL DISTRIBUTION: Europe (Britain*, Denmark, France, Greece, Turkey); N. America (California, USA); S. America (Colombia). *no herbarium material, but recorded by F.A. Mason, The Naturalist no. 848: 270, 1927; on leaves of carnation under glass, Duncombe Park, Helmsley, Yorks. (Sept. 1920). TRANSMISSION: Oospores, which are formed abundantly in the tissues of diseased plants, are thought to be important in disease transmission. A small amount of infection is often seen on the plants in the autumn and these foci can allow the pathogen to overwinter until more favourable weather conditions permit the spread of the disease the following spring. Possible weed hosts for the pathogen such as Cerastium and Stellaria, growing in the vicinity, were examined and found to be infected with a different species of Peronospora belonging to the P. alsinearum group (33, 230).

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Pre- and Postinfection Activity of Fungicides in Control of Hop Downy Mildew

Plant Disease ◽

10.1094/pdis-10-14-1004-re ◽

2015 ◽

Vol 99 (6) ◽

pp. 858-865 ◽

Cited By ~ 3

Author(s):

David H. Gent ◽

Megan C. Twomey ◽

Sierra N. Wolfenbarger ◽

Joanna L. Woods

Keyword(s):

Disease Control ◽

Downy Mildew ◽

Field Experiments ◽

Resistance Management ◽

Field Studies ◽

Similar Efficacy ◽

Application Timing ◽

Pseudoperonospora Humuli ◽

Hazard Warnings ◽

Post Hoc

Optimum timing and use of fungicides for disease control are improved by an understanding of the characteristics of fungicide physical mode of action. Greenhouse and field experiments were conducted to quantify and model the duration of pre- and postinfection activity of fungicides most commonly used for control of hop downy mildew (caused by Pseudoperonospora humuli). In greenhouse experiments, control of downy mildew on leaves was similar among fungicides tested when applied preventatively but varied depending on both the fungicide and the timing of application postinfection. Disease control decreased as applications of copper were made later after inoculation. In contrast, cymoxanil, trifloxystrobin, and dimethomorph reduced disease with similar efficacy when applied 48 h after inoculation compared with preventative applications of these fungicides. When fungicides were applied 72 h after inoculation, only dimethomorph reduced the sporulating leaf area similarly to preinoculation application timing. Adaxial chlorosis, necrosis, and water soaking of inoculated leaves, indicative of infection by P. humuli, were more severe when plants were treated with cymoxanil, trifloxystrobin, and dimethomorph 48 to 72 h after inoculation, even though sporulation was suppressed. Trifloxystrobin and dimethomorph applied 72 h after inoculation suppressed formation of sporangia on sporangiophores as compared with all other treatments. In field studies, dimethomorph, fosetyl-Al, and trifloxystrobin suppressed development of shoots with systemic downy mildew to the greatest extent when applied near the timing of inoculation, although the duration of preventative and postinfection activity varied among the fungicides. There was a small reduction in efficacy of disease control when fosetyl-Al was applied 6 to 7 days after inoculation as compared with protective applications. Trifloxystrobin had 4 to 5 days of preinfection activity and limited postinfection activity. Dimethomorph had the longest duration of protective activity. Percent disease control was reduced progressively with increasing time between inoculation and application of dimethomorph. These findings provide guidance to the use of fungicides when applications are timed with forecasted or post hoc disease hazard warnings, as well as guidance on tank-mixes of fungicides that may be suitable both for resistance management considerations and extending intervals between applications.

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