scholarly journals Natural Occurrence of Microsphaera pulchra and Phyllactinia guttata on Two Cornus Species

Plant Disease ◽  
1998 ◽  
Vol 82 (4) ◽  
pp. 383-385 ◽  
Author(s):  
Leigh Ann Klein ◽  
Mark T. Windham ◽  
Robert N. Trigiano
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Natural Occurrence ◽  
Cornus Florida ◽  
Supplementary Data ◽  
Eastern United States ◽  
Pathogen Identification ◽  
Foliar Disease ◽  
Histological Studies ◽  
Powdery Mildew Fungi

Powdery mildew has become a common foliar disease of Cornus florida and other dogwood species in the eastern United States during the last several years. This study was conducted to determine the identity of powdery mildew fungi on C. florida and C. amomum. Ascocarps of Microsphaera pulchra and Phyllactinia guttata occurred singly and together on both C. florida and C. amomum leaves. M. pulchra ascocarps occurred at a higher density than P. guttata ascocarps on C. florida leaves, whereas P. guttata ascocarps occurred more frequently than M. pulchra ascocarps on C. amomum leaves. Histological studies, however, did not provide supplementary data of infection by the powdery mildew species that occurred less frequently on the leaves of each dogwood species. M. pulchra did not penetrate the cells of C. amomum, and likewise P. guttata did not enter through stomata of C. florida leaves. The presence of ascocarps of both species was not the result of infection of the dogwoods by both pathogens. The ascocarps of M. pulchra probably became airborne and then settled on the C. amomum leaves. Similarly, the ascocarps of P. guttata landed on C. florida leaves. These results emphasize the importance of correct pathogen identification using several criteria such as ascocarp morphology, host-pathogen relationships, distribution of the pathogen, conidial morphology, and histology.

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 Virulence Structure of the Eastern U.S. Wheat Powdery Mildew Population

Plant Disease ◽  
2008 ◽  
Vol 92 (7) ◽  
pp. 1074-1082 ◽  
Author(s):  
Ryan Parks ◽  
Ignazio Carbone ◽  
J. Paul Murphy ◽  
David Marshall ◽  
Christina Cowger
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Geographic Distance ◽  
Restricted Gene Flow ◽  
Eastern United States ◽  
Phenotypic Differences ◽  
Wheat Powdery Mildew ◽  
Detached Leaves ◽  
Geographic Separation ◽  
Wheat Leaves

Little is known about the population structure of wheat powdery mildew in the eastern United States, and the most recent report on virulence in this population involved isolates collected in 1993–94. In the present study, wheat leaves naturally infected with powdery mildew were collected from 10 locations in the southeastern United States in 2003 and 2005 and a collection of 207 isolates was derived from single ascospores. Frequencies of virulence to 16 mildew resistance (Pm) genes were determined by inoculating the isolates individually on replicated plates of detached leaves of differential wheat lines. These virulence frequencies were used to infer local effectiveness of Pm genes, estimate virulence complexity, detect significant associations between pairs of pathogen avirulence loci, and assess whether phenotypic differences between pathogen subpopulations increased with geographic distance. In both years, virulence to Pm3a, Pm3c, Pm5a, and Pm7 was present in more than 90% of sampled isolates and virulence to Pm1a, Pm16, Pm17, and Pm25 was present in fewer than 10% of isolates. In each year, 71 to 88% of all sampled isolates possessed one of a few multilocus virulence phenotypes, although there were significant differences among locations in frequencies of virulence to individual Pm genes. Several significant associations were detected between alleles for avirulence to pairs of Pm genes. Genetic (phenotypic) distance between isolate subpopulations increased significantly (R2 = 0.40, P < 0.001) with increasing geographic separation; possible explanations include different commercial deployment of Pm genes and restricted gene flow in the pathogen population.

scholarly journals Perpetuation of Powdery Mildew Infection and Identification of Erysiphe australiana as the Crape Myrtle Pathogen in Mid-Tennessee

Plant Disease ◽  
2006 ◽  
Vol 90 (8) ◽  
pp. 1098-1101 ◽  
Author(s):  
Ainong Shi ◽  
Margaret T. Mmbaga
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
The United States ◽  
Diagnostic Tools ◽  
Specific Primers ◽  
Standard Polymerase Chain Reaction ◽  
Common Lilac ◽  
Pcr Products ◽  
Powdery Mildew Fungi ◽  
Powdery Mildew Pathogen

The fungus Erysiphe lagerstroemiae is commonly known as the powdery mildew pathogen in crape myrtle (Lagerstroemiae indica) in the United States, and Erysiphe australiana is the powdery mildew pathogen reported in Japan, China, and Australia. The teleomorph often used to identify powdery mildew fungi rarely develops in crape myrtle, and in our observations, ascocarps never formed. Our study showed that the crape myrtle pathogen overwintered as mycelia on dormant buds. The internal transcribed spacer (ITS) regions of rDNA and the intervening 5.8S rRNA gene were amplified using standard polymerase chain reaction (PCR) protocols and the universal primer pairs ITS1 and ITS4. PCR products were analyzed by electrophoresis in a 1.5% agarose gel and sequenced, and the ITS PCR product was 666 bp from ITS1/ITS4 and 704 bp from ITS1-F/ITS4. BLAST analysis of the sequence of the PCR products showed identical similarity with E. australiana reported in Japan, China, and Australia. Comparison of ITS sequences with information in the GenBank on other powdery mildew fungi showed a closest alignment (93% similarity) to Erysiphe juglandis that infects walnut. Specific primers for E. australiana were developed and evaluated for use as diagnostic tools. Out of 12 specific primer pairs evaluated, four primer pairs and four double primer pairs were highly specific to E. australiana and did not amplify Erysiphe pulchra of dogwood, Erysiphe syringae of common lilac, Erysiphe circinata of maple, or Phyllactinia guttata of oak. The E. australiana-specific primers amplified 16 samples of crape myrtle powdery mildew collected from diverse locations in mid-Tennessee. These results clearly showed that the crape myrtle powdery mildew in mid-Tennessee was caused by E. australiana. Specific primers reported in this article provide a diagnostic tool and may be used to confirm the identity of crape myrtle powdery mildew pathogen in other areas in the United States and wherever the disease occurs.

Graminicolous powdery mildew fungi as new natural hosts of Ampelomyces mycoparasites

1997 ◽  
Vol 75 (4) ◽  
pp. 680-683 ◽  
Author(s):  
Levente Kiss
Keyword(s):  
Powdery Mildew ◽  
Poa Pratensis ◽  
Blumeria Graminis ◽  
Erysiphe Graminis ◽  
Natural Occurrence ◽  
Powdery Mildews ◽  
Two Samples ◽  
Natural Hosts ◽  
Powdery Mildew Fungi ◽  
Cultivated Species

The natural occurrence of Ampelomyces mycoparasites is reported for the first time in hyphae, conidiophores, and immature cleistothecia of Blumeria graminis (syn. Erysiphe graminis), the causal agent of cereal and grass powdery mildews. During a 4-year search for Ampelomyces on leaves of different wild and cultivated species of the Gramineae infected with powdery mildews in Hungary, Ampelomyces was recorded in only two samples that represent 5% of the collected monocotyledons. The host plants of B. graminis parasitized by Ampelomyces were Hordeum murinum and Poa pratensis. The pycnidia of Ampelomyces were present in only 3–10% of the powdery mildew mycelia. These observations suggest that (i) the natural occurrence of Ampelomyces mycoparasites on monocotyledons infected with powdery mildews is rare compared with their repeatedly reported incidence on dicotyledons infected with different powdery mildew fungi, and (ii) they probably do not have any significant role in the natural control of B. graminis in the field. Key words: Ampelomyces, Blumeria graminis, Erysiphe graminis, Gramineae, hyperparasitism, mycoparasitism.

scholarly journals Variation in Pathogenicity and Aggressiveness of Erysiphe necator from Different Vitis spp. and Geographic Origins in the Eastern United States

2010 ◽  
Vol 100 (11) ◽  
pp. 1185-1193 ◽  
Author(s):  
Omer Frenkel ◽  
Marin Talbot Brewer ◽  
Michael G. Milgroom
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Lesion Size ◽  
Host Specialization ◽  
Eastern North America ◽  
Eastern United States ◽  
Erysiphe Necator ◽  
Geographic Origins ◽  
Powdery Mildew Pathogen ◽  
Vitis Spp

Eastern North America is considered the center of diversity for many Vitis spp. and for the grape powdery mildew pathogen, Erysiphe necator. However, little is known about populations of E. necator from wild Vitis spp. We determined the phenotypic variation in pathogenicity and aggressiveness of E. necator among isolates from wild and domesticated Vitis spp. from diverse geographic regions in the eastern United States. To test pathogenicity, we inoculated 38 E. necator isolates on three wild Vitis spp., two commercially grown hybrids and the European wine grape, Vitis vinifera. V. rotundifolia (muscadine grape) was the only host species on which complete host specialization was evident; it was only susceptible to isolates collected from V. rotundifolia. All isolates, regardless of source host, were pathogenic on the other Vitis spp. We found no differences in components of aggressiveness latent period and lesion size among isolates from different source hosts when inoculated on V. vinifera, which is highly susceptible to powdery mildew. However significant variation was evident among isolates on the more resistant V. labruscana ‘Niagara’. Isolates from the wild species V. aestivalis were the most aggressive, whereas isolates from V. vinifera were not more aggressive than isolates from other source hosts. Greater aggressiveness was also detected among isolates from the southeastern United States compared with isolates from the northeastern United States.

scholarly journals 549 Three New Cultivars of Flowering Dogwood Resistant to Powdery Mildew

HortScience ◽  
2000 ◽  
Vol 35 (3) ◽  
pp. 490C-490
Author(s):  
R.N. Trigiano ◽  
M.T. Windham ◽  
W.T. Witte
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Partial Resistance ◽  
Control Measure ◽  
Winter Dormancy ◽  
Eastern United States ◽  
Flowering Dogwood ◽  
Nursery Production ◽  
Dogwood Anthracnose ◽  
New Cultivars

Powdery mildew (Microsphaera pulchra) of flowering dogwood (Cornus florida L.) has become a significant problem of trees in nursery production as well as in the landscapes and forests of the eastern United States. The disease significantly reduces growth and berry production by older established trees and may contribute to the inability of younger trees (liners) in production to survive winter dormancy. Disease resistance in named cultivars is limited to partial resistance found in `Cherokee Brave'—all other cultivars are extremely susceptible. Until now, the only disease control measure was to establish an expensive, labor-intensive, preventive fungicide program. We examined >22,000 seedlings and identified 20 that were extremely resistant to powdery mildew. Three trees with white bracts were selected from the 20 and released as patent-pending cultivars. `Karen's Appalachian Blush' has long, non-overlapping, pink fringed bracts with a delicate appearance. `Kay's Appalachian Mist' has creamy white, slightly overlapping bracts with deeply pigmented clefts. `Jean's Appalachian Snow' has large, strongly overlapping bracts with non-pigmented clefts. The three powdery mildew-resistant cultivars will be entered into an existing breeding program with `Appalachian Spring', a cultivar released by the Tennessee Agriculture Experiment Station and resistant to dogwood anthracnose, in an attempt to produce trees that are resistant to both diseases.

scholarly journals Phlox Species Show Quantitative and Qualitative Resistance to a Population of Powdery Mildew Isolates from the Eastern United States

2020 ◽  
Vol 110 (8) ◽  
pp. 1410-1418
Author(s):  
Coralie Farinas ◽  
Pablo S. Jourdan ◽  
Pierce A. Paul ◽  
Jason C. Slot ◽  
Margery L. Daughtrey ◽  
...  
Keyword(s):  
United States ◽  
Genetic Diversity ◽  
Powdery Mildew ◽  
Host Resistance ◽  
Phenotypic Diversity ◽  
Eastern United States ◽  
Significant Information ◽  
Mlst Analysis ◽  
Low Genetic Diversity ◽  
Qualitative Resistance

Ornamental plants in the genus Phlox are extensively planted in landscapes and home gardens around the world. A major limitation to a more widespread use of these plants is their susceptibility to powdery mildew (PM). In this study, we used multilocus sequence typing (MLST) analysis to gain insights into the population diversity of 32 Phlox PM pathogen (Golovinomyces magnicellulatus and Podosphaera sp.) isolates collected from the eastern United States and relate it to the ability to overcome host resistance. Low genetic diversity and a lack of structure were found within our population. Whole genome comparison of two isolates was used to support low genetic diversity evidence found with the MLST analysis. Recombination was suggested by the incongruences observed in the six phylogenetic trees generated from the housekeeping genes TEF-1α, CSI, ITS, IGS, H3, and TUB. Contrasting with low genetic diversity, we found high phenotypic diversity when using 10 of the 32 isolates to evaluate host resistance in four different Phlox species (P. paniculata ‘Dunbar Creek’, P. amoena OPGC 3598, P. glaberrima OPGC 3594, and P. subulata OPGC 4185) using in vitro bioassays. We observed quantitative and qualitative resistance in all Phlox species and a consistent low disease severity in our control, P. paniculata ‘Dunbar Creek’. Taken together, the results generated in this study constitute a robust screening of popular Phlox germplasm that can be incorporated into breeding programs for PM resistance and provides significant information on the evolution of PM pathogens.

scholarly journals Population Diversity and Structure of Podosphaera macularis in the Pacific Northwestern United States and Other Populations

2020 ◽  
Vol 110 (5) ◽  
pp. 1105-1116
Author(s):  
David H. Gent ◽  
Briana J. Claassen ◽  
David M. Gadoury ◽  
Niklaus J. Grünwald ◽  
Brian J. Knaus ◽  
...  
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Population Diversity ◽  
Western United States ◽  
Wild Plants ◽  
Eastern United States ◽  
The Pacific ◽  
Differential Cultivars ◽  
Pathogen Populations ◽  
Podosphaera Macularis

Powdery mildew, caused by Podosphaera macularis, is one of the most important diseases of hop. The disease was first reported in the Pacific Northwestern United States, the primary hop-growing region in this country, in the mid-1990s. More recently, the disease has reemerged in newly planted hopyards of the eastern United States, as hop production has expanded to meet demands of local craft brewers. The spread of strains virulent on previously resistant cultivars, the paucity of available fungicides, and the potential introduction of the MAT1-2 mating type to the western United States, all threaten sustainability of hop production. We sequenced the transcriptome of 104 isolates of P. macularis collected throughout the western United States, eastern United States, and Europe to quantify genetic diversity of pathogen populations and elucidate the possible origins of pathogen populations in the western United States. Discriminant analysis of principal components grouped isolates within three to five geographic populations, dependent on stringency of grouping criteria. Isolates from the western United States were phenotyped and categorized into one of three pathogenic races based on disease symptoms generated on differential cultivars. Western U.S. populations were clonal, irrespective of pathogenic race, and grouped with isolates originating from Europe. Isolates originating from wild hop plants in the eastern United States were genetically differentiated from all other populations, whereas isolates from cultivated hop plants in the eastern United States mostly grouped with isolates originating from the west, consistent with origins from nursery sources. Mating types of isolates originating from cultivated western and eastern U.S. hop plants were entirely MAT1-1. In contrast, a 1:1 ratio of MAT1-1 and MAT1-2 was observed with isolates sampled from wild plants or Europe. Within the western United States a set of highly differentiated loci were identified in P. macularis isolates associated with virulence to the powdery mildew R-gene R6. The weight of genetic and phenotypic evidence suggests a European origin of the P. macularis populations in the western United States, followed by spread of the pathogen from the western United States to re-emergent production regions in the eastern United States. Furthermore, R6 compatibility appears to have been selected from an extant isolate within the western United States. Greater emphasis on sanitation measures during propagation and quarantine policies should be considered to limit further spread of novel genotypes of the pathogen, both between and within production areas.

scholarly journals First Report of Powdery Mildew Caused by an Oidium sp. on Banana Shrub (Michelia figo)

Plant Disease ◽  
1999 ◽  
Vol 83 (2) ◽  
pp. 198-198 ◽  
Author(s):  
G. E. Holcomb
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Baton Rouge ◽  
The United States ◽  
Sexual Stage ◽  
First Report ◽  
Leaf Chlorosis ◽  
Leaf Surfaces ◽  
Powdery Mildew Fungi ◽  
Severity Of The Disease

Banana shrub (Michelia figo (Lour.) Spreng.) is an evergreen grown in southern landscapes in hardiness zones 7 to 9. A powdery mildew disease has been observed sporadically on this plant for several years in the Baton Rouge area during fall months, but symptoms were always mild. During the summer and fall of 1998, banana shrub plants were observed with moderately severe powdery mildew infections that resulted in leaf chlorosis, distortion, and some defoliation. An Oidium sp. was present on both leaf surfaces, but sporulation was more abundant on the abaxial surfaces. Conidia were ellipsoid, produced in chains, devoid of conspicuous fibrosin bodies, and averaged 37 × 19 μm. No sexual stage was found. Conidia brushed from infected leaves to healthy leaves of a potted banana shrub maintained in a greenhouse caused new infections in 5 to 8 days. Factors responsible for the increased severity of the disease in 1998 are unknown, but the unusually dry summer may have contributed to the increased incidence of this disease. An Oidium sp. was listed on M. figo in Australia and the United States (1), but no other reports were found to confirm this. This is the first report of the occurrence of a powdery mildew on M. figo in the United States. Reference: (1) K. Amano. Host Range and Geographical Distribution of the Powdery Mildew Fungi. Japan Scientific Press, Tokyo, 1986.

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