scholarly journals Powdery Mildew Outbreaks caused by Podosphaera macularis on Hop Cultivars Possessing the Resistance Gene R6 in the Pacific Northwestern United States

Plant Disease ◽  
2014 ◽  
Vol 98 (6) ◽  
pp. 852-852 ◽  
Author(s):  
S. N. Wolfenbarger ◽  
E. B. Eck ◽  
C. M. Ocamb ◽  
C. Probst ◽  
M. E. Nelson ◽  
...  
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Resistance Genes ◽  
Washington State ◽  
Cultural Control ◽  
Control Measures ◽  
Crop Damage ◽  
Resistant Cultivars ◽  
Virulent Strains ◽  
The Pacific

Resistant cultivars of hop (Humulus lupulus) have been grown, with the aim of helping to manage powdery mildew in the Pacific Northwest since the first report of the disease in the field in 1997 (4). A major objective of many breeding programs is development of resistance to powdery mildew, and this has generally been achieved by single resistance genes (qualitative resistance). One such gene, R6 (3), has been utilized extensively in new cultivars and has prevented epidemics of the disease in those cultivars across the Pacific Northwestern United States for approximately 15 years. In 2011, a grower in Washington State reported outbreaks of powdery mildew on cv. Apollo, which is thought to possess powdery mildew resistance derived from R6. Fungicides and cultural control measures were applied, and the grower reported no substantial crop damage from the disease. During the winter of 2012, the same grower planted rhizomes of cv. Apollo in a greenhouse in the Yakima Valley of Washington State and later found the plants to be affected by powdery mildew. Affected leaves from plants of cvs. Apollo, Newport, and Nugget (all reported [3] or assumed to possess R6 based on pedigree) grown in the same greenhouse were later provided to the authors. Conidia obtained from each affected plants were transferred to plants of the highly susceptible cv. Symphony, which is not known to contain any resistance genes. After 10 to 14 days of incubation, resultant conidia from each cultivar above (total of three isolates) were transferred to greenhouse grown plants of cvs. Nugget and Symphony and incubated at 18°C. Within 7 days, all three isolates produced powdery mildew colonies characteristic of P. macularis (2) on both cultivars. Cleistothecia did not develop in any colonies. In addition, Nugget and Symphony plants were inoculated with a field population of P. macularis originating from cultivars lacking R6 in Oregon. These inoculations on Nugget did not develop powdery mildew whereas Symphony plants did. Non-inoculated controls remained free of powdery mildew. Results were identical in two additional experiments. The sequence of the mating type idiomorph, MAT1-1, was obtained to confirm identity of the pathogen as P. macularis as described previously (1). The sequences were identical among the three isolates obtained from the greenhouse in Washington and isolates of P. macularis obtained previously from Oregon and Washington. MAT1-2 idiomorph was not detected in the isolates collected. While R6-virulent strains have been detected previously in race characterization experiments, these strains have not caused widespread epidemics of powdery mildew. The increasing prevalence of virulent strains of P. macularis and outbreaks of powdery mildew on formerly resistant cultivars necessitates changes in breeding strategies and disease management efforts to minimize damage resulting from the disease. The distribution of virulent strains of the pathogen and susceptibility of formerly resistance cultivars to powdery mildew are currently under investigation. References: (1) B. Asalfet et al. Phytopathology 103:717, 2013. (2) R. Bélanger et al. The Powdery Mildews: a Comprehensive Treatise. APS Press, St. Paul, MN, 2002. (3) P. Darby. Brew Hist. 121:94, 2005. (4) C. Ocamb et al. Plant Dis. 83:1072, 1999.

Characterization of Resistance to Powdery Mildew in the Hop Cultivars Newport and Comet

2014 ◽  
Vol 15 (2) ◽  
pp. 55-56 ◽  
Author(s):  
Sierra N. Wolfenbarger ◽  
Emily B. Eck ◽  
David H. Gent
Keyword(s):  
Powdery Mildew ◽  
Pacific Northwest ◽  
Host Resistance ◽  
Resistant Cultivars ◽  
Virulent Strains ◽  
The Pacific ◽  
Potential Sources ◽  
Important Disease ◽  
Podosphaera Macularis

Hop powdery mildew, caused by Podosphaera macularis, is an important disease in the Pacific Northwest. Resistant cultivars of hop have been developed and have provided field immunity to the disease until virulent strains of P. macularis emerged. Due to the increase of powdery mildew on formerly resistant cultivars, studies were conducted to characterize potential sources of host resistance. Accepted for publication 5 February 2014. Published 27 March 2014.

Identification of Resistance to Powdery Mildew in Publicly Available Male Hop Germplasm

2018 ◽  
Vol 19 (3) ◽  
pp. 258-264
Author(s):  
David H. Gent ◽  
Briana J. Claassen ◽  
Megan C. Twomey ◽  
Sierra N. Wolfenbarger
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Pacific Northwest ◽  
Western United States ◽  
R Genes ◽  
Sources Of Resistance ◽  
Department Of Agriculture ◽  
Breeding Programs ◽  
The Pacific ◽  
The U.S

Powdery mildew (caused by Podosphaera macularis) is one of the most important diseases of hop in the western United States. Strains of the fungus virulent on cultivars possessing the resistance factor termed R6 and the cultivar Cascade have become widespread in the Pacific Northwestern United States, the primary hop producing region in the country, rendering most cultivars grown susceptible to the disease at some level. In an effort to identify potential sources of resistance in extant germplasm, 136 male accessions of hop contained in the U.S. Department of Agriculture collection were screened under controlled conditions. Iterative inoculations with three isolates of P. macularis with varying race identified 23 (16.9%) accessions with apparent resistance to all known races of the pathogen present in the Pacific Northwest. Of the 23 accessions, 12 were resistant when inoculated with three additional isolates obtained from Europe that possess novel virulences. The nature of resistance in these individuals is unclear but does not appear to be based on known R genes. Identification of possible novel sources of resistance to powdery mildew will be useful to hop breeding programs in the western United States and elsewhere.

scholarly journals Distribution and Characterization of Podosphaera macularis Virulent on Hop Cultivars Possessing R6-Based Resistance to Powdery Mildew

Plant Disease ◽  
2016 ◽  
Vol 100 (6) ◽  
pp. 1212-1221 ◽  
Author(s):  
Sierra N. Wolfenbarger ◽  
Stephen T. Massie ◽  
Cynthia Ocamb ◽  
Emily B. Eck ◽  
Gary G. Grove ◽  
...  
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Mating Type ◽  
Resistance Genes ◽  
Severe Disease ◽  
The United States ◽  
Fitness Cost ◽  
Eastern United States ◽  
Host Genotype ◽  
Podosphaera Macularis

Host resistance, both quantitative and qualitative, is the preferred long-term approach for disease management in many pathosystems, including powdery mildew of hop (Podosphaera macularis). In 2012, an epidemic of powdery mildew occurred in Washington and Idaho on previously resistant cultivars whose resistance was putatively based on the gene designated R6. In 2013, isolates capable of causing severe disease on cultivars with R6-based resistance were confirmed in Oregon and became widespread during 2014. Surveys of commercial hop yards during 2012 to 2014 documented that powdery mildew is now widespread on cultivars possessing R6 resistance in Washington and Oregon, and the incidence of disease is progressively increasing. Pathogenic fitness, race, and mating type of R6-virulent isolates were compared with isolates of P. macularis lacking R6 virulence. All isolates were positive for the mating type idiomorph MAT1-1 and were able to overcome resistance genes Rb, R3, and R5 but not R1 or R2. In addition, R6-virulent isolates were shown to infect differential cultivars reported to possess the R6 gene and also the R4 gene, although R4 has not yet been broadly deployed in the United States. R6-virulent isolates were not detected from the eastern United States during 2012 to 2015. In growth chamber studies, R6-virulent isolates of P. macularis had a significantly longer latent period and produced fewer lesions on plants with R6 as compared with plants lacking R6, indicating a fitness cost to the fungus. R6-virulent isolates also produced fewer conidia when compared with isolates lacking R6 virulence, independent of whether the isolates were grown on a plant with or without R6. Thus, it is possible that the fitness cost of R6 virulence occurs regardless of host genotype. In field studies, powdery mildew was suppressed by at least 50% on plants possessing R6 as compared with those without R6 when coinoculated with R6-virulent and avirulent isolates. R6 virulence in P. macularis appears to be race specific and, at this time, imposes a measurable fitness penalty on the fungus. Resistance genes R1 and R2 appear to remain effective against R6-virulent isolates of P. macularis in the U.S. Pacific Northwest.

scholarly journals First Report of Powdery Mildew, Caused by an Oidium sp., on Poinsettia in California

Plant Disease ◽  
1998 ◽  
Vol 82 (1) ◽  
pp. 128-128 ◽  
Author(s):  
S. T. Koike ◽  
G. S. Saenz
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Pacific Northwest ◽  
The United States ◽  
Euphorbia Pulcherrima ◽  
American Phytopathological Society ◽  
First Report ◽  
The Pacific ◽  
Uninoculated Control ◽  
Alternative Identification

In December 1996 and January 1997, powdery mildew was observed on potted poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) plants in Monterey County, CA. Mycelia were observed on stems, petioles, mature and immature leaves, and bracts. Severely diseased leaves became twisted and bent and senesced prematurely. The white mycelia were conspicuous, epiphytic, and amphigenous; hyphae measured 4.6 to 6.9 μm in diameter. Growth initially was in patches but eventually became effused. Appressoria were slightly lobed to lobed and sometimes opposite. Conidiophore foot cells were cylindrical, sometimes bent at the base, and slightly flexuous to flexuous. Foot cells measured 30.0 to 46.2 μm × 5.8 to 6.9 μm and were followed by one to two shorter cells. Conidia were cylindrical to slightly doliform and measured 25.4 to 32.3 μm × 11.6 to 18.5 μm. The length-to-width ratios of conidia generally were greater than 2.0. Conidia were produced singly, placing the fungus in the Pseudoidium-type powdery mildew group. Conidia germinated at the ends, and no fibrosin bodies were observed. Cleistothecia were not found. The fungus was identified as an Oidium species. Pathogenicity was demonstrated by gently pressing infected leaves having abundant sporulation onto leaves of potted poinsettia plants (cvs. Freedom Red, Peter Star Marble, and Nutcracker White), incubating the plants in a moist chamber for 48 h, and then maintaining plants in a greenhouse. After 12 to 14 days, powdery mildew colonies developed on the inoculated plants, and the pathogen was morphologically identical to the original isolates. Uninoculated control plants did not develop powdery mildew. This is the first report of powdery mildew on poinsettia in California. This fungus appears similar to Microsphaera euphorbiae but has longer, slightly flexuous foot cells that do not match the description for M. euphorbiae (1,2). An alternative identification would be Erysiphe euphorbiae; however, there are no available mitosporic descriptions for morphological comparisons (1,2). In the United States, powdery mildew of poinsettia previously has been reported in various states in the Pacific Northwest, Midwest, and Northeast. References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.

First Report of Powdery Mildew of Myosotis sylvatica (Wood Forget-me-not) Caused by Golovinomyces cynoglossi (Erysiphe cynoglossi) in Washington State

2004 ◽  
Vol 5 (1) ◽  
pp. 18
Author(s):  
Dean A. Glawe
Keyword(s):  
Powdery Mildew ◽  
Pacific Northwest ◽  
Washington State ◽  
Causal Organism ◽  
First Report ◽  
The Pacific ◽  
Western Washington ◽  
Symptoms And Signs

Wood forget-me-not cultivars are popular ornamentals in the Pacific Northwest. In western Washington, this species frequently displays symptoms and signs of powdery mildew after anthesis. This report records the disease from King, Pierce, Snohomish, and Skagit counties and describes and illustrates symptoms of the disease as well as taxonomically important features of the causal organism. Accepted for publication 29 October 2004. Published 24 November 2004.

First Report of Powdery Mildew of Onion (Allium cepa) Caused by Leveillula taurica in the Pacific Northwest

2004 ◽  
Vol 5 (1) ◽  
pp. 17 ◽  
Author(s):  
Lindsey J. du Toit ◽  
Dean A. Glawe ◽  
Gary Q. Pelter
Keyword(s):  
Powdery Mildew ◽  
Pacific Northwest ◽  
Allium Cepa ◽  
Washington State ◽  
Causal Agent ◽  
Columbia Basin ◽  
First Report ◽  
Leveillula Taurica ◽  
The Pacific ◽  
Published Report

A powdery mildew disease of onion has been observed infrequently in the Columbia Basin of Washington State since 1996, but this is the first published report of this disease in the Pacific Northwest. The causal agent was determined to be Leveillula taurica (Lév.) G. Arnaud. Accepted for publication 29 October 2004. Published 29 November 2004.

scholarly journals Adaptation to Partial Resistance to Powdery Mildew in the Hop Cultivar Cascade by Podosphaera macularis

Plant Disease ◽  
2017 ◽  
Vol 101 (6) ◽  
pp. 874-881 ◽  
Author(s):  
David H. Gent ◽  
Stephen T. Massie ◽  
Megan C. Twomey ◽  
Sierra N. Wolfenbarger
Keyword(s):  
Powdery Mildew ◽  
Partial Resistance ◽  
Quantitative Resistance ◽  
Washington State ◽  
R Genes ◽  
Powdery Mildew Fungus ◽  
Field Surveys ◽  
The Pacific ◽  
Qualitative Resistance ◽  
Podosphaera Macularis

The hop cultivar Cascade has been grown in the Pacific Northwestern U.S. and elsewhere with minimal input for management of powdery mildew (Podosphaera macularis) for nearly 15 years due to the putatively quantitative resistance in this cultivar. While partial resistance is generally thought to be more durable than qualitative resistance, in 2012, powdery mildew was reported on Cascade in Washington State. Field surveys conducted during 2013 to 2016 indicated increasing prevalence of powdery mildew on Cascade, as well as an increasing number of fungicide applications applied to this cultivar in Washington State. Nearly all isolates of P. macularis tested were able to infect Cascade in laboratory inoculations. However, the greatest number of colonies, most conidia produced, and the shortest latent period was only observed with isolates derived originally from Cascade, as compared with other isolates derived from other cultivars. Further, the enhanced aggressiveness of these isolates was only manifested on Cascade and not six other susceptible cultivars, further indicating a specific adaptation to Cascade by the isolates. There was no evidence of a known major R-gene in Cascade, as seven isolates of P. macularis with contrasting virulence all infected Cascade. Among 158 isolates obtained from hop yards planted to Cascade, only two (1.3%) were able to infect the cultivar Nugget, which possesses the resistance factor termed R6, indicating that isolates of P. macularis virulent on Nugget are largely distinct from those adapted to Cascade. Further, race characterization indicated Cascade-adapted isolates of P. macularis were able to overcome R-genes Rb, R3, and R5, but not other known R-genes. Therefore, multiple R-genes and other sources of partial resistance are expected to provide resistance to Cascade-adapted strains of the fungus. Given the plasticity of the powdery mildew fungus, breeding strategies for powdery mildew need to consider the potential for adaptation to both qualitative and partial resistance in the host.

First Report of Powdery Mildew of Magnolia Caused by Microsphaera magnifica (Erysiphe magnifica) in the Pacific Northwest

2003 ◽  
Vol 4 (1) ◽  
pp. 37
Author(s):  
Dean A. Glawe
Keyword(s):  
United States ◽  
North America ◽  
Powdery Mildew ◽  
Pacific Northwest ◽  
Western United States ◽  
First Report ◽  
Landscape Plant ◽  
First Finding ◽  
The Pacific ◽  
First Time

Magnolia liliiflora Desrousseaux in Lamarck (orthographic variant: M. liliiflora), a species thought to have originated in China (3), is used as a landscape plant in North America. In August 2002, Microsphaera magnifica U. Braun was collected from three plants of M. liliiflora in the Magnolia collection at the Washington Park Arboretum, University of Washington, Seattle. This report documents for the first time a powdery mildew disease of a Magnolia species in the Pacific Northwest, and the first finding of M. magnifica in the western United States. Accepted for publication 14 April 2003. Published 12 May 2003.

Development of Management Strategies for Hop Powdery Mildew in the Pacific Northwest

2001 ◽  
Vol 2 (1) ◽  
pp. 8 ◽  
Author(s):  
William W. Turechek ◽  
Walter F. Mahaffee ◽  
Cynthia M. Ocamb
Keyword(s):  
Powdery Mildew ◽  
Pacific Northwest ◽  
Management Practices ◽  
Management Strategies ◽  
Control Measures ◽  
Laboratory Studies ◽  
The Pacific ◽  
Sphaerotheca Macularis ◽  
Serious Disease ◽  
Sound Management

Hop powdery mildew, caused by Sphaerotheca macularis, was first discovered in the Yakima Valley of Washington in 1997 and has since become the most serious disease of hop (Humulus lupus) in the Pacific Northwest. Lack of understanding of the epidemiology of S. macularis has made it difficult to develop sound management practices. Results from our field and laboratory studies suggest that control measures applied early in the growing season are probably the most important in shaping the epidemic in a particular field and that late season control measures may not need to be applied at the same intensity as in early to mid-season. Accepted for publication 9 March 2001. Published 13 March 2001.

A new invasive hawkweed, Hieracium glomeratum (Lactuceae, Asteraceae), in the Pacific Northwest

2006 ◽  
Vol 84 (1) ◽  
pp. 133-142 ◽  
Author(s):  
Linda M. Wilson ◽  
Judith Fehrer ◽  
Siegfried Bräutigam ◽  
Gitta Grosskopf
Keyword(s):  
United States ◽  
North America ◽  
Pacific Northwest ◽  
The United States ◽  
Washington State ◽  
Dna Fingerprints ◽  
Distribution Map ◽  
Invasive Potential ◽  
The Pacific ◽  
Eastern Washington

During the summer of 2001, a newly recorded species of exotic hawkweed ( Hieracium glomeratum Froel.) for North America was identified from specimens collected in southeastern British Columbia, Canada, and eastern Washington state, United States. The specimens had previously been identified as the closely related Hieracium caespitosum Dumort. DNA fingerprints of plants from different localities proved to be identical. Their clonality, along with a spot-like distribution, indicates that this apomictic species probably originated from a single introduction from Europe, which subsequently spread. This species adds to the complex of 14 other exotic Hieracium species belonging to the Eurasian subgenus Pilosella that are adventive in the United States and Canada. A distribution map of the native and adventive range of H. glomeratum, and a key to distinguish it from related species in subgenus Pilosella that occur in North America are provided. The evolutionary and invasive potential of H. glomeratum is also discussed.

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