scholarly journals A Two-Phase Resistance Response of Venturia inaequalis Populations to the QoI Fungicides Kresoxim-Methyl and Trifloxystrobin

Plant Disease ◽  
2004 ◽  
Vol 88 (5) ◽  
pp. 537-544 ◽  
Author(s):  
Wolfram Köller ◽  
D. M. Parker ◽  
W. W. Turechek ◽  
Cruz Avila-Adame ◽  
Keith Cronshaw
Keyword(s):  
Cytochrome B ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Target Site ◽  
Site Mutation ◽  
Two Phase ◽  
Resistance Response ◽  
Population Responses ◽  
North Germany ◽  
Qoi Resistance

The class of fungicides acting as respiration inhibitors by binding to the Qo center of cyto-chrome b (QoIs) are in wide use for the management of apple scab caused by Venturia inaequalis. In order to assess responses of V. inaequalis populations to treatments with QoIs, sensitivities of isolates were determined for germinating conidia or for mycelial colonies developing from germinating conidia. Under both test conditions, inhibitory potencies of kresoxim-methyl and trifloxystrobin were largely equivalent. V. inaequalis populations treated with QoIs in a commercial and an experimental orchard both responded with significant shifts toward declining QoI sensitivities. However, the population responses were quantitative in nature, and highly resistant isolates indicative of a cytochrome b target site mutation were not detected. V. inaequalis populations from both orchards investigated also were fully resistant to sterol de-methylation-inhibiting fungicides (DMIs) such as fenarimol and myclobutanil, but isolate sensitivities to QoIs and DMIs were largely unrelated. Performance tests with kresoxim-methyl and trifloxystrobin at the experimental orchard diagnosed as DMI-resistant revealed that the quantitative shift toward declining QoI sensitivities did not constitute the status of practical QoI resistance. In contrast to these quantitative responses, emergence of qualitative QoI resistance was documented for V. inaequalis in an orchard in North Germany, which had been treated intensively with a total of 25 QoI applications over four consecutive seasons. Isolates retrieved from the orchard were highly resistant to both kresoxim-methyl and trifloxystrobin and were characterized as G143A cytochrome b mutants. The results indicated that the paths of QoI resistance can be both quantitative and qualitative in nature. A similar phenomenon has not been described before. Circumstantial evidence suggests that the quantitative phase of V. inaequalis population responses to QoIs might be succeeded by a quantitative selection of highly resistant G143A target-site mutants.

scholarly journals Heteroplasmy of the cytochrome b Gene in Venturia inaequalis and Its Involvement in Quantitative and Practical Resistance to Trifloxystrobin

2014 ◽  
Vol 104 (9) ◽  
pp. 945-953 ◽  
Author(s):  
Sara M. Villani ◽  
Kerik D. Cox
Keyword(s):  
Cytochrome B ◽  
Relative Abundance ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Cyt B ◽  
Resistance Response ◽  
Relative Growth ◽  
Qoi Fungicides ◽  
Cyt B Gene ◽  
Moderate Resistance

Quantitative (partial) and qualitative (complete) resistance responses to quinone outside inhibitor (QoI) fungicides have been documented for the apple scab pathogen Venturia inaequalis. Resistance monitoring efforts have traditionally focused on the detection of qualitative resistance based on a single point mutation, G143A, within the cytochrome b (cyt b) gene. In order to better understand the role of heteroplasmy of the cyt b gene in the QoI resistance response for isolates and populations of V. inaequalis, an allele-specific quantitative polymerase chain reaction was developed to quantify the relative abundance of the A143 (resistant) allele in 45 isolates of V. inaequalis with differing in vitro resistance responses to the QoI fungicide trifloxystrobin. Although a high relative abundance of the A143 allele (>62%) was associated with isolates with high resistance responses (50 to 100% relative growth on trifloxystrobin-amended medium), heteroplasmy of the cyt b gene was not the primary factor involved in isolates with moderate resistance responses (29 to 49% relative growth). The relative abundance of the A143 allele in isolates with moderate resistance to trifloxystrobin rarely exceeded 8%, suggesting that other resistance mechanisms are involved in moderate resistance and, therefore, that the Qol resistance response is polygenic. In research orchards where QoI fungicides failed to control apple scab (practical resistance), field trials were conducted to demonstrate the link between practical resistance and the abundance of the A143 allele. Relative abundance of the A143 allele in these orchard populations exceeded 20% in 2011 and 2012. Similarly, of the eight additional commercial orchards screened in 2011, the relative abundance of the A143 allele always exceeded 20% in those with QoI practical resistance. Although heteroplasmy of the cyt b gene did not entirely explain the response of isolates with moderate resistance to QoIs, the relative abundance of A143 in orchard populations of V. inaequalis helps to explain the point of emergence for practical resistance to trifloxystrobin across several orchard populations with differing production histories.

scholarly journals First Report of QoI Resistance in Venturia inaequalis Causing Apple Scab in Apple Orchards in Turkey

Plant Disease ◽  
2016 ◽  
Vol 100 (5) ◽  
pp. 1016-1016 ◽  
Author(s):  
C. Turan ◽  
I. M. Nanni ◽  
N. Tosun ◽  
M. Collina
Keyword(s):  
Venturia Inaequalis ◽  
Apple Scab ◽  
Apple Orchards ◽  
First Report ◽  
Qoi Resistance

Occurrence of quinone outside inhibitor (QoI) resistance in Virginia populations of Parastagonospora nodorum infecting wheat

Plant Disease ◽  
2020 ◽  
Author(s):  
Navjot Kaur ◽  
Chase Mullins ◽  
Nathan Michael Kleczewski ◽  
Hillary Laureen Mehl
Keyword(s):  
Cytochrome B ◽  
Management Practices ◽  
Cultural Practices ◽  
Resistance Management ◽  
Cytochrome B Gene ◽  
Target Site ◽  
Quinone Outside Inhibitor ◽  
Parastagonospora Nodorum ◽  
The U.S ◽  
Qoi Resistance

Stagonospora nodorum blotch (SNB) of wheat, caused by Parastagonospora nodorum, is managed using cultural practices, resistant varieties, and foliar fungicides. Frequent fungicide use can select for fungicide resistance, making certain chemistries less effective; this may in part explain increasing severity of SNB in the mid-Atlantic U.S. Quinone outside inhibitor (QoI) resistance has been documented for a diversity of fungi, but it has not been reported for P. nodorum in the U.S. The objectives of this study were to 1) evaluate QoI sensitivity of P. nodorum from Virginia wheat fields, 2) screen P. nodorum for QoI target site mutations in the cytochrome b gene, and 3) develop a molecular assay to detect target site mutations associated with QoI resistance. Sensitivity of 16 isolates to pyraclostrobin and azoxystrobin was evaluated with radial growth assays, and the cytochrome b gene was sequenced. One isolate was insensitive to both fungicides, and it had the G143A mutation in the cytochrome b gene. For azoxystrobin, 10 isolates without target site mutations had reduced sensitivity. Additional isolates (N=74) were sequenced, and seven had the G143A mutation; all seven isolates with the mutation had reduced sensitivity to pyraclostrobin and azoxystrobin compared to a sensitive control isolate without the mutation. A pyrosequencing assay targeting G143A was developed as a rapid method to screen P. nodorum for the QoI resistance-conferring mutation. To our knowledge, this is the first report of QoI resistant P. nodorum in the U.S. Overall resistance frequency was low, but resistance management practices are needed to maintain the efficacy of fungicides for SNB control.

Occurrence of QoI Resistance and Detection of the G143A Mutation in Michigan Populations of Venturia inaequalis

Plant Disease ◽  
2011 ◽  
Vol 95 (8) ◽  
pp. 927-934 ◽  
Author(s):  
Kimberley E. Lesniak ◽  
Tyre J. Proffer ◽  
Janna L. Beckerman ◽  
George W. Sundin
Keyword(s):  
Spore Germination ◽  
Control Strategies ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Pathogenic Fungi ◽  
Qoi Fungicides ◽  
Widespread Occurrence ◽  
Scab Control ◽  
High Level ◽  
Qoi Resistance

Control strategies for Venturia inaequalis rely heavily on chemical fungicides. Single-site fungicides such as the quinone-outside inhibitors (QoI) have been used in Michigan apple orchards for more than 11 years. In 2008, we sampled eight commercial orchards in the Fruit Ridge growing region of Michigan in which apple scab control failures were observed on ‘McIntosh’ apple following applications of kresoxim-methyl or trifloxystrobin. QoI resistance was assessed in 210 total isolates (a total of 17 orchards) using a spore germination assay and in 319 isolates using a polymerase chain reaction (PCR) assay to detect the G143A mutation located within the V. inaequalis cytochrome b gene (CYTB). The G143A mutation is known to confer high-level QoI resistance in plant-pathogenic fungi. QoI resistance was confirmed in 50 and 64% of the isolates tested with the spore germination and PCR assays, respectively, and there was a 97% concordance observed between the assays. In 2009, we sampled and examined an additional 1,201 V. inaequalis isolates from 64 orchards in Michigan and 86 isolates from four baseline sites in Ohio. All of these isolates were assayed for the G143A mutation and it was detected within 67 and 0% of the Michigan and Ohio isolates, respectively. Our results indicate the widespread occurrence of QoI resistance in Michigan commercial orchard populations of V. inaequalis. Loss of QoI fungicides further limits the arsenal of fungicides available to commercial apple growers for successful scab management.

scholarly journals Prevalence and Stability of Qualitative QoI Resistance in Populations of Venturia inaequalis in the Northeastern United States

Plant Disease ◽  
2014 ◽  
Vol 98 (8) ◽  
pp. 1122-1130 ◽  
Author(s):  
Zachary A. Frederick ◽  
Sara M. Villani ◽  
Daniel R. Cooley ◽  
Alan R. Biggs ◽  
Jessica J. Raes ◽  
...  
Keyword(s):  
United States ◽  
Venturia Inaequalis ◽  
Effective Means ◽  
Apple Scab ◽  
Northeastern United States ◽  
Qoi Fungicides ◽  
Quinone Outside Inhibitor ◽  
Management Paradigms ◽  
The Stability ◽  
Qoi Resistance

Quinone-outside-inhibitor (QoI) fungicides are a safe and effective means of managing apple scab caused by Venturia inaequalis. To determine the prevalence of both quantitative (partial) and qualitative (complete) QoI resistance in V. inaequalis in the northeastern United States, we sampled single-lesion conidial isolates (n = 4,481) from 120 commercial and research orchards from 2004 to 2011 with a range of exposure to QoI fungicides from none to several applications a year. In all, 67% of these orchard populations of V. inaequalis were sensitive to QoI fungicides, 28% exhibited QoI practical resistance, and 5% were not sensitive QoI fungicides but had not become practically resistant. Isolates with qualitative QoI resistance, conferred by the G143A cytochrome b gene mutation, were found in 13 of the 34 QoI-resistant orchard populations. To evaluate the stability of the G143A mutation, 27 isolates were selected from different orchard populations to represent the scope of regional populations. These isolates were subcultured continuously in the presence or absence of the QoI fungicide trifloxystrobin. All isolates that initially possessed qualitative resistance maintained the resistant genotype (G143A) for six transfers over 6 months in both the absence and presence of trifloxystrobin. Given the observed QoI resistance in orchard populations of V. inaequalis and the stability of the G143A mutation in individual isolates, apple scab management paradigms must encompass strategies to limit selection of QoI resistance in the sensitive orchard populations remaining in the region.

scholarly journals Two Receptor-Like Genes, Vfa1 and Vfa2, Confer Resistance to the Fungal Pathogen Venturia inaequalis Inciting Apple Scab Disease

2008 ◽  
Vol 21 (4) ◽  
pp. 448-458 ◽  
Author(s):  
Mickael Malnoy ◽  
Mingliang Xu ◽  
Ewa Borejsza-Wysocka ◽  
Schuyler S. Korban ◽  
Herb S. Aldwinckle
Keyword(s):  
Fungal Pathogen ◽  
Southern Blotting ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Microscopic Analysis ◽  
Chain Reaction ◽  
Resistance Response ◽  
Malus Floribunda ◽  
Apple Cultivars ◽  
Polymerase Chain

The Vf locus, originating from the crabapple species Malus floribunda 821, confers resistance to five races of the fungal pathogen Venturia inaequalis, the causal agent of apple scab disease. Previously, a cluster of four receptor-like genes, Vfa1, Vfa2, Vfa3, and Vfa4, was identified within the Vf locus. Because the amino-acid sequence of Vfa3 is truncated, it was deemed nonfunctional. In this study, each of the three full-length Vfa genes was introduced into a plant cloning vector, pCAMBIA2301, and used for Agrobacterium-mediated transformation of two apple cultivars, Galaxy and McIntosh, to assess functionality of these genes and to characterize their roles in resistance to V. inaequalis. Transformed apple lines carrying each of Vfa1, Vfa2, or Vfa4 were developed, analyzed for the presence of the transgene using polymerase chain reaction and Southern blotting, and assayed for resistance to apple scab following inoculation with V. inaequalis. Transformed lines expressing Vfa4 were found to be susceptible to apple scab, whereas those expressing either Vfa1 or Vfa2 exhibited partial resistance to apple scab. Based on Western blot analysis as well as microscopic analysis of plant resistance reactions, the roles of Vfa1 and Vfa2 in apple scab disease resistance response are discussed.

Distribution of G143A mutations conferring fungicide resistance in Virginia populations of Parastagonospora nodorum infecting wheat

2021 ◽  
Author(s):  
Navjot Kaur ◽  
Hillary Mehl
Keyword(s):  
Fungicide Resistance ◽  
Cultural Control ◽  
Target Site ◽  
Leaf Spot Disease ◽  
Site Mutation ◽  
Quinone Outside Inhibitor ◽  
Management Approaches ◽  
Pathogen Populations ◽  
Parastagonospora Nodorum ◽  
Qoi Resistance

Stagonospora nodorum blotch (SNB) caused by Parastagonospora nodorum is an important leaf spot disease in the mid-Atlantic U.S. Disease management approaches include use of resistant varieties, cultural control, and foliar fungicides. Frequent use of foliar fungicides can select for fungicide resistance within pathogen populations. Recently, the first report of quinone outside inhibitor (QoI) fungicide resistance in the U.S. was made based on a relatively small collection of P. nodorum isolates from Virginia. The objective of this study was to conduct a state-wide, two-year survey of P. nodorum populations in Virginia wheat and quantify frequencies of the target-site mutation that confers QoI resistance. A total of 318 isolates of P. nodorum were obtained from wheat collected at seven locations distributed throughout the wheat-growing regions of Virginia in 2018 and 2019. A previously designed pyrosequencing assay that detects the G143A substitution in the cytochrome b gene of P. nodorum was used to screen isolates for the presence or absence of the target site mutation. The G143A substitution was detected in all sampled fields. Among locations and years, frequencies of the mutation in P. nodorum populations ranged from 5-32% (mean = 19%). Thus, the QoI-resistance conferring G143A mutation was widespread in P. nodorum populations in Virginia and it occurred at a relatively high frequency. Results suggest that fungicides containing QoI active ingredients may not be effective for controlling SNB in Virginia and the surrounding region, and application of stand-alone QoI fungicides for disease control in wheat is not recommended.

Constituents from Morus root bark against Venturia inaequalis – the causal agent of apple scab

Planta Medica ◽  
2007 ◽  
Vol 73 (09) ◽  
Author(s):  
JM Rollinger ◽  
R Spitaler ◽  
M Menz ◽  
P Schneider ◽  
EP Ellmerer ◽  
...  
Keyword(s):  
Venturia Inaequalis ◽  
Apple Scab ◽  
Causal Agent ◽  
Root Bark

scholarly journals Apple Autotetraploids with Enhanced Resistance to Apple Scab (Venturia inaequalis) Due to Genome Duplication-Phenotypic and Genetic Evaluation

2021 ◽  
Vol 22 (2) ◽  
pp. 527
Author(s):  
Małgorzata Podwyszyńska ◽  
Monika Markiewicz ◽  
Agata Broniarek-Niemiec ◽  
Bożena Matysiak ◽  
Agnieszka Marasek-Ciolakowska
Keyword(s):  
Venturia Inaequalis ◽  
Leaf Shape ◽  
Apple Scab ◽  
Early Period ◽  
Physiological Parameters ◽  
Aflp Analysis ◽  
Poor Growth ◽  
Enhanced Resistance ◽  
Apple Cultivars ◽  
Old Trees

Among the fungal diseases of apple trees, serious yield losses are due to an apple scab caused by Venturia inaequalis. Protection against this disease is based mainly on chemical treatments, which are currently very limited. Therefore, it is extremely important to introduce cultivars with reduced susceptibility to this pathogen. One of the important sources of variability for breeding is the process of polyploidization. Newly obtained polyploids may acquire new features, including increased resistance to diseases. In our earlier studies, numerous tetraploids have been obtained for several apple cultivars with ‘Free Redstar’ tetraploids manifesting enhanced resistance to apple scab. In the present study, tetraploids of ‘Free Redstar’ were assessed in terms of phenotype and genotype with particular emphasis on the genetic background of their increased resistance to apple scab. Compared to diploid plants, tetraploids (own-rooted plants) were characterized with poor growth, especially during first growing season. They had considerably shorter shoots, fewer branches, smaller stem diameter, and reshaped leaves. In contrast to own-rooted plants, in M9-grafted three-year old trees, no significant differences between diplo- and tetraploids were observed, either in morphological or physiological parameters, with the exceptions of the increased leaf thickness and chlorophyll content recorded in tetraploids. Significant differences between sibling tetraploid clones were recorded, particularly in leaf shape and some physiological parameters. The amplified fragment length polymorphism (AFLP) analysis confirmed genetic polymorphism of tetraploid clones. Methylation-sensitive amplification polymorphism (MSAP) analysis showed that the level of DNA methylation was twice as high in young tetraploid plants as in a diploid donor tree, which may explain the weaker vigour of neotetraploids in the early period of their growth in the juvenile phase. Molecular analysis showed that ‘Free Redstar’ cultivar and their tetraploids bear six Rvi genes (Rvi5, Rvi6, Rvi8, Rvi11, Rvi14 and Rvi17). Transcriptome analysis confirmed enhanced resistance to apple scab of ‘Free Redstar’ tetraploids since the expression levels of genes related to resistance were strongly enhanced in tetraploids compared to their diploid counterparts.

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