scholarly journals The Effect of Delayed-Dormant Chemical Treatments on Demethylation Inhibitor (DMI) Sensitivity in a DMI-resistant Population of Venturia inaequalis

Plant Disease ◽  
2015 ◽  
Vol 99 (12) ◽  
pp. 1751-1756 ◽  
Author(s):  
Zachary A. Frederick ◽  
Sara M. Villani ◽  
Kerik D. Cox
Keyword(s):  
New York ◽  
Treatment Program ◽  
Management Practices ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Fungicide Treatment ◽  
Chemical Treatments ◽  
Dmi Fungicides ◽  
The Impact ◽  
Demethylation Inhibitor

Demethylation inhibitor (DMI) fungicides are an effective means to manage apple scab caused by Venturia inaequalis. Unfortunately, practical resistance to DMI fungicide chemistries is prevalent in populations in New York and the New England states. Management practices that delay the development of DMI resistance in V. inaequalis populations are highly desired by regional apple producers. Trials were conducted in a New York apple orchard during the 2011 and 2012 growing seasons to determine the impact of delayed-dormant (after bud break, but prior to green tissue) chemical treatments on the DMI sensitivity of a V. inaequalis population with stable resistance to DMI fungicides. Delayed-dormant treatment programs consisted of either an application of a copper fungicide, a manganese sanitation product, a DMI fungicide (myclobutanil), or no fungicide. Sensitivity to the DMI fungicide myclobutanil was evaluated for a minimum of 25 V. inaequalis single lesion conidial isolates from each of four replicated treatment blocks. In both years, mean percent relative growth on myclobutanil amended media for V. inaequalis isolates from the copper treatment program were significantly (P < 0.05) lower than isolates from blocks did not receive a delayed dormant fungicide treatment. The effect of the manganese treatment was inconsistent between years. V. inaequalis isolates collected from the myclobutanil treatment program were not significantly (P > 0.05) different in myclobutanil sensitivity from isolates collected from the blocks that did not receive a delayed dormant fungicide treatment. Overall, the results suggest that delayed dormant treatments of copper may favorably impact the myclobutanil sensitivity for a population of V. inaequalis with resistance to DMI fungicides, and should be considered as a standard management practice in apple production.

scholarly journals Orchard Factors Associated with Resistance and Cross Resistance to Sterol Demethylation Inhibitor Fungicides in Populations of Venturia inaequalis from Pennsylvania

2012 ◽  
Vol 102 (3) ◽  
pp. 272-282 ◽  
Author(s):  
Emily E. Pfeufer ◽  
Henry K. Ngugi
Keyword(s):  
Odds Ratio ◽  
Management Practices ◽  
Venturia Inaequalis ◽  
Cross Resistance ◽  
Single Spore ◽  
Quantitative Evidence ◽  
Development Of Resistance ◽  
Orchard Management ◽  
Dmi Fungicides ◽  
Demethylation Inhibitor

Orchard management practices, such as destroying of overwintered inoculum and limiting the number of fungicide applications, are often recommended as tactics for slowing the development of resistance to sterol demethylation-inhibitor (DMI) fungicides in populations of Venturia inaequalis. However, there is little quantitative evidence relating the use of such practices to levels of resistance in orchards. The aim of this study was to evaluate the sensitivity of V. inaequalis isolates from Pennsylvania to DMI fungicides, and to identify orchard management factors related to the incidence of resistant isolates. In total, 644 single-spore V. inaequalis cultures obtained from 20 apple orchards in 2008 or 2009 were tested for sensitivity to myclobutanil, fenbuconazole, or difenoconazole. Growers provided management history of the sampled plots. Widespread shifts toward resistance to the three fungicides were noted, with mean effective concentration for 50% inhibition (EC50) values of 2.136, 0.786, and 0.187 μg/ml for myclobutanil, fenbuconazole, and difenoconazole, respectively. Cross resistance to the three fungicides was documented in high correlation (Spearman's r > 0.6) between mean EC50 values for 14 orchards. Based on a 0.5-μg/ml threshold, 66 and 26% of isolates were resistant to myclobutanil and fenbuconazole, respectively, and 22% were cross resistant to the two fungicides. A significant between-year shift toward increased resistance was noted in two of three orchards surveyed in both years. Failure to use dormant copper sprays, older trees, larger orchards, orchards with ≤10 cultivars, and application of >4 DMI sprays were positively correlated (0.0001 < P < 0.05) with the incidence of resistant isolates. Isolates from orchards with >4 DMI sprays were four times as likely to be resistant to fenbuconazole (odds ratio = 4.57; P = 0.015). Isolates from orchards without dormant copper sprays were twice as likely to be cross-shifted toward resistance to all three fungicides (odds ratio = 1.76; P = 0.048). Results identify management practices that can reduce the risk of V. inaequalis developing resistance to DMI fungicides.

scholarly journals Selection Preferences for Crabapple Cultivars and Species

2003 ◽  
Vol 13 (3) ◽  
pp. 522-526 ◽  
Author(s):  
James P. Romer ◽  
Jeffery K. Iles ◽  
Cynthia L. Haynes
Keyword(s):  
New York ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
The United States ◽  
Geographic Region ◽  
The West ◽  
Public And Private ◽  
West Central ◽  
Wide Range ◽  
Growth Habits

Crabapples (Malus spp.) are commonly planted ornamental trees in public and private landscapes. Hundreds of selections are available that represent a wide range of growth habits, ornamental traits, and varying degrees of resistance/susceptibility to disease. We distributed 1810 questionnaires in 13 states (Oregon, Washington, Utah, Colorado, Minnesota, Iowa, Missouri, Illinois, Indiana, Michigan, Ohio, New York, and Pennsylvania) to members of either nursery and landscape associations or the Associated Landscape Contractors of America (ACLA, Herndon, Va.) to identify crabapple preferences across a broad geographic region of the United States. We also were interested in learning if regional disease problems were important to green-industry professionals as they decide which crabapples to include in their inventories. Our respondent population numbered 511 (28.2% response rate). A large percentage of respondents (79.4%) said their retail clients focused mostly on fl ower color when choosing crabapples for the home landscape, while commercial clients showed slightly more interest in growth habit (32.5%) than fl ower color (28.7%). `Prairifire' was identified by respondents in all regions, except the west-central (Colorado and Utah), as the crabapple most frequently recommended to clients when tree size is not important. Respondents in the west-central region most often (48.7%) recommend the fruitless selection `Spring Snow'. Respondents in all regions, except the west-central, identified apple scab (Venturia inaequalis) as the most prevalent crabapple disease and named scab-susceptible `Radiant' as the selection most frequently discontinued.

scholarly journals Overexpression of the CYP51A1 Gene and Repeated Elements are Associated with Differential Sensitivity to DMI Fungicides in Venturia inaequalis

2016 ◽  
Vol 106 (6) ◽  
pp. 562-571 ◽  
Author(s):  
Sara M. Villani ◽  
Jon Hulvey ◽  
Jean-Michel Hily ◽  
Kerik D. Cox
Keyword(s):  
Regression Analysis ◽  
Linear Regression ◽  
Illumina Sequencing ◽  
Venturia Inaequalis ◽  
Linear Regression Analysis ◽  
Differential Sensitivity ◽  
Transcriptional Enhancer ◽  
Relative Growth ◽  
Dmi Fungicides ◽  
Demethylation Inhibitor

The involvement of overexpression of the CYP51A1 gene in Venturia inaequalis was investigated for isolates exhibiting differential sensitivity to the triazole demethylation inhibitor (DMI) fungicides myclobutanil and difenoconazole. Relative expression (RE) of the CYP51A1 gene was significantly greater (P < 0.0001) for isolates with resistance to both fungicides (MRDR phenotype) or with resistance to difenoconazole only (MSDR phenotype) compared with isolates that were resistant only to myclobutanil (MRDS phenotype) or sensitive to both fungicides (MSDS phenotype). An average of 9- and 13-fold increases in CYP51A1 RE were observed in isolates resistant to difenoconazole compared with isolates with MRDS and MSDS phenotypes, respectively. Linear regression analysis between isolate relative growth on myclobutanil-amended medium and log10 RE revealed that little to no variability in sensitivity to myclobutanil could be explained by CYP51A1 overexpression (R2 = 0.078). To investigate CYP51A1 upstream anomalies associated with CYP51A1 overexpression or resistance to difenoconazole, Illumina sequencing was conducted for three isolates with resistance to difenoconazole and one baseline isolate. A repeated element, “EL 3,1,2”, with the properties of a transcriptional enhancer was identified two to four times upstream of CYP51A1 in difenoconazole-resistant isolates but was not found in isolates with the MRDS phenotype. These results suggest that different mechanisms may govern resistance to different DMI fungicides in the triazole group.

scholarly journals Spatial and Temporal Factors Associated with an Increased Prevalence of Listeria monocytogenes in Spinach Fields in New York State

2015 ◽  
Vol 81 (17) ◽  
pp. 6059-6069 ◽  
Author(s):  
Daniel Weller ◽  
Martin Wiedmann ◽  
Laura K. Strawn
Keyword(s):  
New York ◽  
Foodborne Pathogens ◽  
Management Practices ◽  
New York State ◽  
Content Type ◽  
Detection Frequency ◽  
Temporal Factors ◽  
Allele Type ◽  
Rain Events ◽  
The Impact

ABSTRACTWhile rain and irrigation events have been associated with an increased prevalence of foodborne pathogens in produce production environments, quantitative data are needed to determine the effects of various spatial and temporal factors on the risk of produce contamination following these events. This study was performed to quantify these effects and to determine the impact of rain and irrigation events on the detection frequency and diversity ofListeriaspecies (includingL. monocytogenes) andL. monocytogenesin produce fields. Two spinach fields, with high and low predicted risks ofL. monocytogenesisolation, were sampled 24, 48, 72, and 144 to 192 h following irrigation and rain events. Predicted risk was a function of the field's proximity to water and roads. Factors were evaluated for their association withListeriaspecies andL. monocytogenesisolation by using generalized linear mixed models (GLMMs). In total, 1,492 (1,092 soil, 334 leaf, 14 fecal, and 52 water) samples were collected. According to the GLMM, the likelihood ofListeriaspecies andL. monocytogenesisolation from soil samples was highest during the 24 h immediately following an event (odds ratios [ORs] of 7.7 and 25, respectively). Additionally,Listeriaspecies andL. monocytogenesisolates associated with irrigation events showed significantly lowersigBallele type diversity than did isolates associated with precipitation events (P= <0.001), suggesting that irrigation water may be a point source ofL. monocytogenescontamination. Small changes in management practices (e.g., not irrigating fields before harvest) may therefore reduce the risk ofL. monocytogenescontamination of fresh produce.

scholarly journals Evaluation of Tactics for Managing Resistance of Venturia inaequalis to Sterol Demethylation Inhibitors

Plant Disease ◽  
1999 ◽  
Vol 83 (9) ◽  
pp. 857-863 ◽  
Author(s):  
Wolfram Köller ◽  
W. F. Wilcox
Keyword(s):  
Venturia Inaequalis ◽  
Apple Scab ◽  
Run Off ◽  
Equivalent Control ◽  
Sterol Demethylation Inhibitors ◽  
The Individual ◽  
And Control ◽  
The Impact ◽  
Low Rate ◽  
Selection Of

The impact on the selection and control of subpopulations of V. inaequalis resistant to the sterol demethylation inhibitor (DMI) fenarimol or to dodine were evaluated with respect to several tactics of apple scab control. Experiments were conducted in an experimental orchard with elevated levels of DMI and dodine resistance over a period of three consecutive seasons. The DMI-resistant subpopulation was poorly (14%) controlled at a fenarimol rate of 15 mg/liter (sprayed to run-off), whereas control was significantly improved (54%) at twice that rate. Mancozeb mixed with the low rate of fenarimol also improved the control of DMI-resistant isolates, but the improvement was due to the indiscriminate control of both the DMI-sensitive and -resistant populations provided by mancozeb. The selection of fenarimol-resistant isolates resulting from poor control of the resistant subpopulation by the low rate of fenarimol was equivalent whether fenarimol was applied singly or in mixture with mancozeb. Consequently, the use of high DMI rates in mixture with a protective fungicide is expected to delay the build-up of resistant subpopulations by limiting their increase through two separate principles of control. For dodine in mixture with fenarimol, it was found that each mixing partner applied alone selected both fe-narimol- and dodine-resistant isolates. This selection pattern was partly explained by the possibility that one of the multiple genes underlying fenarimol and dodine resistance confers resistance to both fungicides, in addition to the selection of double-resistant isolates. Regardless, a mixture of fenarimol with dodine each employed at a low rate controlled both the fenarimol-and the dodine-resistant subpopulation at least as effectively as the individual components at twice their mixture rate, and an accelerated selection of double-resistant isolates was not detected. In commercial orchard trials, mixtures of DMIs with either a protective fungicide or with dodine provided equivalent control even when levels of DMI resistance, dodine resistance, or both were moderately elevated. With the exception of orchards with high levels of DMI or dodine resistance, dodine might be an alternative to protective fungicides as a mixing partner with DMIs.

scholarly journals Prevalence of Myclobutanil Resistance and Difenoconazole Insensitivity in Populations of Venturia inaequalis

Plant Disease ◽  
2015 ◽  
Vol 99 (11) ◽  
pp. 1526-1536 ◽  
Author(s):  
Sara M. Villani ◽  
Alan R. Biggs ◽  
Daniel R. Cooley ◽  
Jessica J. Raes ◽  
Kerik D. Cox
Keyword(s):  
New England ◽  
Field Experiments ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Apple Fruit ◽  
Scab Control ◽  
Dmi Fungicides ◽  
Commercial Research ◽  
Mature Apple ◽  
Single Lesion

Demethylation inhibitors (DMIs) are a class of single-site fungicides with high levels of protective and curative efficacy against Venturia inaequalis, the causal agent of apple scab. To determine the prevalence of resistance to the DMI fungicide myclobutanil, 3,987 single-lesion conidial V. inaequalis isolates from 141 commercial, research, and baseline orchard populations were examined throughout New England, the mid-Atlantic, and the Midwest from 2004 to 2013. Of these orchard populations, 63% had practical resistance, 13% had reduced sensitivity, and 24% were sensitive to myclobutanil. A sensitivity baseline for the recently introduced DMI fungicide difenoconazole was established to make comparisons with myclobutanil sensitivity in orchard populations. The mean effective concentration of difenoconazole at which mycelial growth was inhibited by 50% (EC50) was determined to be 0.002 μg ml−1 for 44 baseline isolates of V. inaequalis. From 2010 to 2013, 1,012 isolates of V. inaequalis from 37 of the 141 orchard populations above were screened for sensitivity to difenoconazole. In all, 1 orchard population had reduced sensitivity to difenoconazole, while the remaining 36 orchard populations were sensitive to the fungicide. In field experiments, difenoconazole demonstrated high levels of apple scab control on mature apple fruit, despite the fact that the population of V. inaequalis had practical resistance to difenoconazole. Although our results indicate widespread resistance to myclobutanil but not difenoconazole, due to the propensity for cross-sensitivity among DMI fungicides, growers with myclobutanil resistance should be cautious when using difenoconazole for disease management.

scholarly journals Sensitivity of Venturia inaequalis to myclobutanil penconazole and dodine in relation to fungicide use in Hawkes Bay apple orchards

2012 ◽  
Vol 65 ◽  
pp. 106-113
Author(s):  
R.M. Beresford ◽  
P.J. Wright ◽  
P.N. Wood ◽  
N.M. Park
Keyword(s):  
Venturia Inaequalis ◽  
Resistance Management ◽  
Black Spot ◽  
High Sensitivity ◽  
Fruit Production ◽  
Apple Orchards ◽  
Management Guidelines ◽  
Dmi Fungicides ◽  
Integrated Fruit Production ◽  
Demethylation Inhibitor

A survey of Integrated Fruit Production and organic apple orchards in Hawkes Bay in 201011 investigated sensitivity of Venturia inaequalis isolates to demethylation inhibitor (DMI) and dodine fungicides EC50 values from mycelial growth assays for two DMIs showed continued loss of sensitivity since the 1990s Sensitivity was lower in orchards where DMI usage exceeded resistance management guidelines The most DMIsensitive isolates were found in one organic orchard Plant inoculations showed that black spot control of myclobutanilresistant V inaequalis strains by one application of myclobutanil was only 55 compared with 99 for myclobutanilsensitive strains The study suggests that resistance to DMI fungicides has continued to develop that loss of black spot control could be expected in some orchards and that DMI resistance management guidelines need reviewing There was high sensitivity to dodine in all orchards (mean EC50 of 024 mg/litre) and no evidence of increased resistance since the 1990s

scholarly journals New North American isolates of Venturia inaequalis can overcome apple scab resistance of Malus floribunda 821

2019 ◽  
Author(s):  
David Papp ◽  
Jugpreet Singh ◽  
David Gadoury ◽  
Awais Khan
Keyword(s):  
New York ◽  
Genetic Structure ◽  
Population Genetic Structure ◽  
Population Genetic ◽  
Venturia Inaequalis ◽  
Durable Resistance ◽  
Apple Scab ◽  
Scab Resistance ◽  
Breeding Programs ◽  
Malus Floribunda

AbstractApple scab, caused by Venturia inaequalis (Cke.) Wint., is a destructive fungal disease of major apple cultivars worldwide, most of which are moderately to highly susceptible. Thus, development of scab resistant cultivars is one of the highest priorities of apple breeding programs. The principal source of resistance for breeding programs has been the scab resistance gene Rvi6 that originated from the Japanese crabapple Malus floribunda (Sieb.) sel. 821. Isolates of V. inaequalis able to overcome Rvi6 have been identified in Europe, but have not yet been reported on the American continents. We recently discovered scab infection on M. floribunda 821 trees in a research orchard at Geneva, New York, USA, where approximately 10% of the leaves bore profusely sporulating apple scab lesions, many of which had coalesced to cover entire leaves. Chlorosis and pinpoint pitting symptoms typical of failed infections by V. inaequalis on hosts bearing the Rvi6 and Rvi7 genes were also observed. We assessed genetic diversity and population genetic structure of six V. inaequalis isolates collected from M. floribunda 821, one isolate from ‘Nova Easygro’, one isolate from ‘Golden Delicious’ and two isolates from Europe (11 isolates in total) using 16,321 genome-wide SNPs. Population genetic structure and PCA separated the isolates into distinct European and USA groups. The forgoing suggests that the new Rvi6 virulent isolates emerged within USA populations, rather than being transported from Europe. The overcoming of resistance in M. floribunda 821 but not in descendant cultivars suggests that durable resistance to apple scab will require a more comprehensive understanding of Rvi6 mediated resistance in diverse genetic backgrounds.

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