Fungicide programs used to manage powdery mildew (Erysiphe necator) in Australian vineyards

Management of grape powdery mildew (Erysiphe necator) using quinone outside inhibitors (QoIs) has eroded in an increasing number of regions due to resistance development. To determine persistence of resistance when QoIs are withdrawn, competition assays were conducted on unsprayed grape plants (Vitis vinifera ‘Chardonnay’) by cycling mixtures of resistant and sensitive isolates characterized as genetically diverse based on microsatellite analyses. Under laboratory conditions, %G143A, quantified by quantitative polymerase chain reaction (qPCR), increased significantly, indicating competitiveness of the resistant fraction. To confirm competitiveness in the field, trials using potted plants were conducted. Percent G143A tended to decrease in one growing season, probably due to spore migration and mixing of populations with natural background inoculum. In a second season, QoI resistance persisted at high frequency for 4 weeks. Resistant populations were also found to persist in one vineyard without QoI application for four consecutive years. The frequency was still about 25% in the fourth year, with higher frequency (36%) in a hotspot section. QoI-resistant populations with >5% G143A also harbored Y136F in the cyp51 gene that confers some resistance to sterol demethylation inhibitors, another fungicide class for powdery mildew control. Double resistance could have been partly responsible for persistence of QoI resistance at this location.

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Identification of Race-Specific Resistance in North American Vitis spp. Limiting Erysiphe necator Hyphal Growth

Phytopathology ◽

10.1094/phyto-03-11-0062 ◽

2012 ◽

Vol 102 (1) ◽

pp. 83-93 ◽

Cited By ~ 15

Author(s):

David W. Ramming ◽

Franka Gabler ◽

Joseph L. Smilanick ◽

Dennis A. Margosan ◽

Molly Cadle-Davidson ◽

...

Keyword(s):

Powdery Mildew ◽

Resistance Genes ◽

Specific Resistance ◽

Hyphal Growth ◽

Resistance Mechanisms ◽

Hybrid Breeding ◽

Erysiphe Necator ◽

Vitis Rotundifolia ◽

Resistance Sources

Race-specific resistance against powdery mildews is well documented in small grains but, in other crops such as grapevine, controlled analysis of host–pathogen interactions on resistant plants is uncommon. In the current study, we attempted to confirm powdery mildew resistance phenotypes through vineyard, greenhouse, and in vitro inoculations for test cross-mapping populations for two resistance sources: (i) a complex hybrid breeding line, ‘Bloodworth 81-107-11', of at least Vitis rotundifolia, V. vinifera, V. berlandieri, V. rupestris, V. labrusca, and V. aestivalis background; and (ii) Vitis hybrid ‘Tamiami’ of V. aestivalis and V. vinifera origin. Statistical analysis of vineyard resistance data suggested the segregation of two and three race-specific resistance genes from the two sources, respectively. However, in each population, some resistant progeny were susceptible in greenhouse or in vitro screens, which suggested the presence of Erysiphe necator isolates virulent on progeny segregating for one or more resistance genes. Controlled inoculation of resistant and susceptible progeny with a diverse set of E. necator isolates clearly demonstrated the presence of fungal races differentially interacting with race-specific resistance genes, providing proof of race specificity in the grape powdery mildew pathosystem. Consistent with known race-specific resistance mechanisms, both resistance sources were characterized by programmed cell death of host epidermal cells under appressoria, which arrested or slowed hyphal growth; this response was also accompanied by collapse of conidia, germ tubes, appressoria, and secondary hyphae. The observation of prevalent isolates virulent on progeny with multiple race-specific resistance genes before resistance gene deployment has implications for grape breeding strategies. We suggest that grape breeders should characterize the mechanisms of resistance and pyramid multiple resistance genes with different mechanisms for improved durability.

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Genetic Structure and Aggressiveness of Erysiphe necator Populations during Grapevine Powdery Mildew Epidemics

Applied and Environmental Microbiology ◽

10.1128/aem.01200-08 ◽

2008 ◽

Vol 74 (20) ◽

pp. 6327-6332 ◽

Cited By ~ 30

Author(s):

Josselin Montarry ◽

Philippe Cartolaro ◽

François Delmotte ◽

Jérôme Jolivet ◽

Laetitia Willocquet

Keyword(s):

Powdery Mildew ◽

Latency Period ◽

Growing Season ◽

Spore Production ◽

Erysiphe Necator ◽

Genetic Groups ◽

Grapevine Powdery Mildew ◽

Temporal Differentiation ◽

Group A ◽

Group B

ABSTRACT Isolates of the causal ascomycete of grapevine powdery mildew, Erysiphe necator, correspond to two genetically differentiated groups (A and B) that coexist on the same host. This coexistence was analyzed by investigating temporal changes in the genetic and phenotypic structures of E. necator populations during three epidemics. Group A was present only at the start of the growing season, whereas group B was present throughout all three epidemics. Group A was less aggressive in terms of germination and infection efficiency but was more aggressive than group B in terms of the latency period, lesion diameter, and spore production. Our results are consistent with a temporal differentiation of niches, preventing recombination, and suggest an association between the disease level and the frequencies of genetic groups.

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Strobilurin (QoI) Resistance in Populations of Erysiphe necator on Grapes in Michigan

Plant Disease ◽

10.1094/pdis-01-12-0041-re ◽

2012 ◽

Vol 96 (11) ◽

pp. 1621-1628 ◽

Cited By ~ 15

Author(s):

L. A. Miles ◽

T. D. Miles ◽

W. W. Kirk ◽

A. M. C. Schilder

Keyword(s):

Powdery Mildew ◽

Fungicide Resistance ◽

Resistance Management ◽

The United States ◽

Suboptimal Control ◽

Single Nucleotide ◽

Erysiphe Necator ◽

Nucleotide Mutation ◽

Conidium Germination ◽

Qoi Resistance

Powdery mildew, caused by Erysiphe necator, is the most common and destructive disease of grapes (Vitis spp.) worldwide. In Michigan, it is primarily controlled with fungicides, including strobilurins (quinone outside inhibitors [QoIs]). Within the United States, resistance to this class of fungicides has been reported in E. necator populations in some east coast states. Among 12 E. necator isolates collected from five Michigan vineyards in 2008, one carried the G143A single-nucleotide mutation responsible for QoI resistance. This isolate was confirmed to be resistant in a conidium germination assay on water agar amended with trifloxystrobin at 0.001, 0.01, 0.1, 1, 10, or 100 μg/ml and salicylhydroxamic acid (100 mg/liter). The mutant isolate was able to germinate on media amended with 100 μg/ml trifloxystrobin, whereas a representative wild-type isolate did not germinate at concentrations higher than 0.1 μg/ml. In 2009, 172 isolates were collected from a total of 21 vineyards (juice and wine grapes): three vineyards with no fungicide application history (baseline sites), six research vineyards, and 12 commercial vineyards. QoI resistance was defined as the effective concentration that inhibited 50% of conidial germination (EC50) > 1 μg/ml. Isolates from baseline sites had EC50 values mostly below 0.01 μg/ml, while isolates that were highly resistant to trifloxystrobin (EC50 > 100 μg/ml) occurred in five research and three commercial wine grape vineyards at frequencies of 40 to 100% and 25 to 75% of the isolates, respectively. The G143A mutation was detected in every isolate with an EC50 > 1 μg/ml. These results suggest that fungicide resistance may play a role in suboptimal control of powdery mildew observed in some Michigan vineyards and emphasizes the need for continued fungicide resistance management.

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Adaptive genomic structural variation in the grape powdery mildew pathogen, Erysiphe necator

BMC Genomics ◽

10.1186/1471-2164-15-1081 ◽

2014 ◽

Vol 15 (1) ◽

pp. 1081 ◽

Cited By ~ 65

Author(s):

Laura Jones ◽

Summaira Riaz ◽

Abraham Morales-Cruz ◽

Katherine CH Amrine ◽

Brianna McGuire ◽

...

Keyword(s):

Powdery Mildew ◽

Structural Variation ◽

Erysiphe Necator ◽

Genomic Structural Variation ◽

Powdery Mildew Pathogen ◽

Grape Powdery Mildew

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Differential Gene Expression During Conidiation in the Grape Powdery Mildew Pathogen, Erysiphe necator

Phytopathology ◽

10.1094/phyto-11-10-0295 ◽

2011 ◽

Vol 101 (7) ◽

pp. 839-846 ◽

Cited By ~ 12

Author(s):

Laura Wakefield ◽

David M. Gadoury ◽

Robert C. Seem ◽

Michael G. Milgroom ◽

Qi Sun ◽

...

Keyword(s):

Gene Expression ◽

Powdery Mildew ◽

Differential Gene Expression ◽

Polymorphism Analysis ◽

Erysiphe Necator ◽

Powdery Mildews ◽

Differential Gene ◽

Powdery Mildew Pathogen ◽

Fungal Genes ◽

Grape Powdery Mildew

Asexual sporulation (conidiation) is coordinately regulated in the grape powdery mildew pathogen Erysiphe necator but nothing is known about its genetic regulation. We hypothesized that genes required for conidiation in other fungi would be upregulated at conidiophore initiation or full conidiation (relative to preconidiation vegetative growth and development of mature ascocarps), and that the obligate biotrophic lifestyle of E. necator would necessitate some novel gene regulation. cDNA amplified fragment length polymorphism analysis with 45 selective primer combinations produced ≈1,600 transcript-derived fragments (TDFs), of which 620 (39%) showed differential expression. TDF sequences were annotated using BLAST analysis of GenBank and of a reference transcriptome for E. necator developed by 454-FLX pyrosequencing of a normalized cDNA library. One-fourth of the differentially expressed, annotated sequences had similarity to fungal genes of unknown function. The remaining genes had annotated function in metabolism, signaling, transcription, transport, and protein fate. As expected, a portion of orthologs known in other fungi to be involved in developmental regulation was upregulated immediately prior to or during conidiation; particularly noteworthy were several genes associated with the light-dependent VeA regulatory system, G-protein signaling (Pth11 and a kelch repeat), and nuclear transport (importin-β and Ran). This work represents the first investigation into differential gene expression during morphogenesis in E. necator and identifies candidate genes and hypotheses for characterization in powdery mildews. Our results indicate that, although control of conidiation in powdery mildews may share some basic elements with established systems, there are significant points of divergence as well, perhaps due, in part, to the obligate biotrophic lifestyle of powdery mildews.

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