Pseudoperonospora humuli. [Descriptions of Fungi and Bacteria].

1983 ◽  
Author(s):  
S. M. Francis
Keyword(s):  
Downy Mildew ◽  
Geographical Distribution ◽  
Systemic Infection ◽  
Humulus Lupulus ◽  
Convincing Evidence ◽  
Cone Production ◽  
Secondary Infections ◽  
Pseudoperonospora Humuli ◽  
Growing Crop ◽  
Curled Leaves

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.

Peronospora anemones. [Descriptions of Fungi and Bacteria].

1981 ◽  
Author(s):  
S. M. Francis
Keyword(s):  
New Zealand ◽  
Botrytis Cinerea ◽  
Downy Mildew ◽  
Geographical Distribution ◽  
Primary Infection ◽  
Leaf Surface ◽  
Plant Debris ◽  
Lower Leaf Surface ◽  
Glass Slides ◽  
Secondary Infections

Abstract A description is provided for Peronospora anemones. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Anemone coronaria, A. globosa. DISEASE: Downy mildew of anemones. Infected leaves lose their natural bloom, appearing dull green, almost grey in colour and are often down curled giving the plant a rounded appearance. As the disease progresses, leaf colour may change to shades of pink or purple with necrotic areas appearing on the older leaves. Invasion by secondary organisms (e.g. Botrytis cinerea) is common, especially after frost or storm injury, and this accelerates plant death. In favourable conditions conidiophores develop forming a whitish-grey down on the lower leaf surface, on the bracts and, less frequently, on the petioles. It is not uncommon for affected plants to show little or no sporulation and in these cases the presence of extensive intercellular mycelium and, later in the season, oospores in petioles and peduncles helps diagnosis. GEOGRAPHICAL DISTRIBUTION: Australasia (New Zealand); Europe (England, Jersey, France, Italy, Netherlands). TRANSMISSION: Primary infection is caused by oospores in plant debris in the soil. Tramier (1963) was unable to germinate oospores and thus work out precise details of the conditions affecting their germination but he showed evidence that regular and prolonged rain encouraged germination. Conidia, which cause secondary infections, are dispersed by rain and during harvesting of the flowers. Wind is thought to be unimportant in their dissemination as shown by glass slides covered with vaseline and placed near an infected crop (Tramier, 1965).

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

2019 ◽  
Vol 109 (8) ◽  
pp. 1354-1366 ◽  
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.

Peronospora dianthicola. [Descriptions of Fungi and Bacteria].

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).

Peronospora trifoliorum. [Descriptions of Fungi and Bacteria].

1983 ◽  
Author(s):  
S. M. Francis
Keyword(s):  
Medicago Sativa ◽  
Downy Mildew ◽  
Geographical Distribution ◽  
Systemic Infection ◽  
Seed Transmission ◽  
Field Conditions ◽  
Infected Leaf ◽  
Light Green

Abstract A description is provided for Peronospora trifoliorum. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Medicago sativa subsp. saliva, M. sativa subsp. falcata. DISEASE: Downy mildew of lucerne (alfalfa). Infected leaflets, which tend to be near the top of the stem, are light green or yellow. The affected areas can vary from small localized spots to larger areas of infected leaf or a systemic infection where the entire shoot may become yellow, stunted and swollen. GEOGRAPHICAL DISTRIBUTION: Worldwide, wherever lucerne is grown. CMI Map No. 343 includes records on clover and other hosts. TRANSMISSION: Mycelium is reported to overwinter in the crown bud (42, 617). Conidia are produced the following spring and in damp and humid conditions soon spread the disease. Oospores occur but reports on their frequency under field conditions are so few that it is difficult to assess their importance in overwintering the disease. Seed transmission, though suspected by Eriksson (1930) and also reported from Italy in a sample of seed from Argentina (Campbell, 1922), is thought to be unimportant (Richardson, 1979).

Bremia lactucae. [Descriptions of Fungi and Bacteria].

1981 ◽  
Author(s):  
W. M. Morgan
Keyword(s):  
Geographical Distribution ◽  
Systemic Infection ◽  
Lower Surface ◽  
Globe Artichoke ◽  
Bremia Lactucae ◽  
Lettuce Plant ◽  
Mature Leaves ◽  
Secondary Infections ◽  
Important Means ◽  
Means Of Transmission

Abstract A description is provided for Bremia lactucae. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: At least 230 species in the following genera of Compositae: Agoseris, Arctium, Carduus, Carthamus, Centaurea, Cichorium, Cineraria, Cirsium, Crepis, Cynara, Dendroseris, Dimorphotheca, Erechtites, Gaillardia, Gnaphalium, Helichrysum, Hemistepta, Hieracium, Hypochoeris, Jacobaea, Knightia, Lactuca, Lagoseris, Lapsana, Lappa, Leontodon, Mulgedium, Nabalus, Picris, Prenanthes, Rhodanthe, Saussurea, Senecio, Solidago, Sonchus, Taraxacum and Tragopogon. DISEASE: 'Downy mildew' of lettuce, globe artichoke, endive, chicory and many ornamental and wild species of Compositae. Infection can occur on any part of the lettuce plant (Lactuca sativa) except the capitulum (40: 197) and the fungus may colonize the plant systemically even as far as the roots (42: 429). In infected seedlings, the cotyledons stop growing, leading to stunting or death of the plant. Sporulation occurs on both sides of the cotyledon, which becomes chlorotic. As seedlings age, they become less susceptible, systemic infection becomes progressively less and fewer sporangiophores are produced (53, 3262). Newly formed true leaves are less susceptible than cotyledons (53, 3262). On mature leaves, profuse sporulation on the lower surface is sometimes preceded by a slight chlorosis; in widespread infections of wrapper leaves conidiophores are often the first sign of infection. On the upper surface chlorosis becomes severe and the lesion, bounded by the main veins, is frequently angular in appearance. Browning may occur later, probably due to secondary infections. On globe artichoke (Cynara scolymus) infection of the peduncle and basal bracts allows access to secondary infections (43, 3104). GEOGRAPHICAL DISTRIBUTION: World-wide except Antarctica and Arctic (CMI Map 86, ed. 3, 1969). TRANSMISSION: Sporulation is usually profuse and conidia are air-borne. Conidia from cultivated lettuce are viable for at least 60 days at low temperatures and high humidity (40: 197) and, where lettuce is grown throughout the year, conidia are the most important means of transmission of the disease. The fungus is probably also carried over from season to season by means of oospores in soil debris (51, 3663).

Sensitivity of Pseudoperonospora humuli (the Causal Agent of Hop Downy Mildew) from Oregon, Idaho, and Washington to Fosetyl-Al (Aliette)

2004 ◽  
Vol 5 (1) ◽  
pp. 4 ◽  
Author(s):  
Mark E. Nelson ◽  
Kenneth C. Eastwell ◽  
Gary G. Grove ◽  
James D. Barbour ◽  
Cynthia M. Ocamb ◽  
...  
Keyword(s):  
Downy Mildew ◽  
Dose Response ◽  
Humulus Lupulus ◽  
Leaf Disk ◽  
Causal Agent ◽  
Response Curves ◽  
Pseudoperonospora Humuli ◽  
Dose Response Curves ◽  
Northern Idaho

Failures of fosetyl-Al (Aliette) to control hop (Humulus lupulus) downy mildew, caused by Pseudoperonospora humuli, have recently occurred in northern Idaho and Oregon. To determine if resistance of the pathogen to the fungicide has developed, leaf disk assays were conducted to compare sensitivity of P. humuli isolates from the different U.S. hop-growing regions to isolates from a research yard where exposure to fosetyl-Al had not occurred for at least 10 years. Dose response curves of transformed data were linear. The fosetyl-Al concentration effective against 50% of the P. humuli isolates (ED50) from each location was estimated from the linearized data. The ED50 values indicate that fosetyl-Al was about one-third as effective against P. humuli isolates from commercial hop yards in northern Idaho and Oregon and about one-half as effective against isolates from southern Idaho compared to isolates from the research yard. Commercial yards in Washington were similar to the research yard. Accepted for publication 3 August 2004. Published 11 August 2004.

Hop Downy Mildew Caused by Pseudoperonospora humuli: A Diagnostic Guide

2020 ◽  
Vol 21 (3) ◽  
pp. 173-179 ◽  
Author(s):  
Savithri Purayannur ◽  
Timothy D. Miles ◽  
David H. Gent ◽  
Stacey Pigg ◽  
Lina M. Quesada-Ocampo
Keyword(s):  
Host Range ◽  
Downy Mildew ◽  
Geographical Distribution ◽  
Management Practices ◽  
Pseudoperonospora Humuli

Downy mildew, caused by Pseudoperonospora humuli, is one of the most destructive diseases of hop. The purpose of this article is to provide an overview of the pathogen, the host range and geographical distribution, and the means to diagnose the disease. It is important to be able to diagnose downy mildew and distinguish it from other diseases for the timely application of suitable management practices. The procedures for laboratory propagation and maintenance of isolates are also presented.

Peronospora antirrhini. [Descriptions of Fungi and Bacteria].

1981 ◽  
Author(s):  
S. M. Francis
Keyword(s):  
Downy Mildew ◽  
Geographical Distribution ◽  
Seed Transmission ◽  
Lower Surface ◽  
Flowering Plants ◽  
Antirrhinum Majus ◽  
High Humidity ◽  
Secondary Infections ◽  
Leaf Surfaces ◽  
Definite Proof

Abstract A description is provided for Peronospora antirrhini. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Antirrhinum majus, A. nuttallianum, Misopates orontium. DISEASE: Downy mildew of antirrhinum. This is mainly a disease of seedlings and young plants. The infection is systemic and affected plants appear stunted and pale yellowish-green. The leaves are curled inwards and droop down. Conidiophores develop on the lower surface forming a fine white to purple down. In heavy infections the down is found on both leaf surfaces and also on the stems. The growing point may be killed and then plants often break from the base and produce several new shoots. Conidia can cause secondary infections on the leaves of older plants especially in conditions of high humidity. These appear as pale yellowish spots. GEOGRAPHICAL DISTRIBUTION: Worldwide, see CMI Map No. 222 ed. 2, 1971. TRANSMISSION: Seed transmission by oospores was tentatively suggested by Yarwood (1947). Moore & Moore (1952) refer to circumstantial evidence but say there is no definite proof. Peronospora antirrhini is not recorded as a seed pathogen by Richardson (1979) but Neergaard (1977) points out that for seed-borne infection of a downy mildew to be effective all that is needed is a mere trace of the fungus on the seed. As Yarwood (1947) indicates, terminal infections of flowering plants could easily contaminate seed.

Pseudoperonospora humuli. [Distribution map].

1986 ◽  
Author(s):  
Keyword(s):  
New York ◽  
North America ◽  
South America ◽  
Geographical Distribution ◽  
Buenos Aires ◽  
Humulus Lupulus ◽  
Washington State ◽  
Distribution Map ◽  
Pseudoperonospora Humuli ◽  
New Distribution

Abstract A new distribution map is provided for Pseudoperonospora humuli (Miyabe & Tak.) G.W. Wilson. Hosts: Hop (Humulus lupulus) 0012-396X. Information is given on the geographical distribution in ASIA, China (N.E.), India, Japan, Korea, USSR (Azerbaijan), (Kazakhstan), (Kirghizia), EUROPE, Austria, Belgium, Britain (England), Scotland, Bulgaria, Czechoslovakia, Finland, France, Germany, Greece, Hungary, Irish Republic, Italy, Netherlands, Norway, Poland, Portugal, Romania, Spain, Sweden, Switzerland, USSR (N.W., Caucasus), (Belorussia, Estonia, Latvia, Lithuania, Ukraine), Yugoslavia, NORTH AMERICA, Canada, USA (California, New York, Oregon, Washington State, Wisconsin), SOUTH AMERICA, Argentina (Buenos Aires).

scholarly journals Hop Downy Mildew Caused by Pseudoperonospora humuli in Argentina

Plant Disease ◽  
2009 ◽  
Vol 93 (8) ◽  
pp. 839-839 ◽  
Author(s):  
B. A. Pérez ◽  
E. Martínez ◽  
F. Noetinger ◽  
E. R. Wright
Keyword(s):  
Downy Mildew ◽  
Disease Incidence ◽  
Phosphorous Acid ◽  
Systemic Infection ◽  
First Record ◽  
Early Spring ◽  
Fungicide Treatment ◽  
Rio Negro ◽  
Pseudoperonospora Humuli ◽  
Downy Mildew Disease

In Argentina, hop downy mildew disease caused by Pseudoperonospora humuli first appeared in Alto Valle of Rio Negro and Neuquen (1957), Mar del Plata (1962), and El Bolson (1963) (1). The disease occurred in the hop (Humulus lupulus L.) planting areas of El Bolson (Rio Negro) and Lago Pueblo (Chubut) in 2002 and 2003. Surveys were conducted in 30 commercial hop fields from December 2002 to March 2003 to estimate disease incidence and susceptibility of cultivars planted in these fields. Hop fields were divided into five sections and 100 plants were randomly selected and assessed for the presence of disease. Symptoms that were observed in early spring included dark brown rootstocks and primary basal spikes (stunted plants with pale and curled leaves), which are characteristic of systemic infection. Later in the season, secondary infections were characterized by dark purple-to-black lesions on leaves, flowers, cones, and lateral and terminal spikes. Plant symptoms and fungal morphological markers (dichotomously branched sporangiophores; ellipsoid and papillate sporangia) agreed with hop downy mildew disease and the fungus P. humuli. Yield loss was estimated as the reduction in yield compared with the 2001–2002 season observed from five hop growers. On December 10, 70% of the hop fields had greater than 50% disease incidence and seven fields reached 100% incidence. The reduction in cone yield varied between 20 and 34% in fields without a rootstock fungicide treatment. One field with a rootstock fungicide treatment (mefenoxam, copper oxiclorure, phosphorous acid, copper sulfate, and fosetyl-Al) and regular fungicide applications had a 30% increase in cone yield compared with 2001–2002. Systemically infected plants were recorded for hop cvs. Bullion, Cascade, CEZ, GS-19, Hallertauer Mfr., Nugget, Spalt, and Traful. Previously, Cascade was rated as a resistant cultivar to the root systemic infection (1). To our knowledge, this is the first record of a hop downy mildew outbreak in Argentina during the last 30 years. Reference: (1) L. Leskovar. El Lúpulo: Su Cultivo y Procesamiento. Hemisferio Sur. Buenos Aires, 1978.

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