Identification of Putative SDHI Target Site Mutations in the SDHB, SDHC, and SDHD Subunits of the Grape Powdery Mildew Pathogen Erysiphe necator

Development and Implementation of a Novel CAPS Assay Reveals High Prevalence of a Boscalid Resistance Marker and Its Co-Occurrence with an Azole Resistance Marker in Erysiphe necator

Succinate dehydrogenase inhibitors (SDHIs) are frequently used against powdery mildew (PM) fungi, such as Erysiphe necator, the causal agent of grapevine PM. Fungicide resistance, however, hinders effective control. DNA-based monitoring facilitates the recognition of resistance. We aimed (i) to adapt an effective method to detect a widespread genetic marker of resistance to boscalid, a commonly used SDHI, and (ii) to study the co-occurrence of the marker with a marker of resistance to demethylase inhibitor (DMI) fungicides. Sequencing of the sdhB gene identified a nonsynonymous substitution, denoted as sdhB-A794G, leading to an amino acid change (H242R) in the sdhB protein. In vitro fungicide resistance tests showed that E. necator isolates carrying sdhB-A794G were resistant to boscalid. We adopted a cleaved amplified polymorphic sequence-based method and screened more than 500 field samples collected from five Hungarian wine regions in two consecutive years. The sdhB-A794G marker was detected in all wine regions and in both years, altogether in 61.7% of samples, including 20.5% in which both sdhB-A794G and the wild-type were present. The frequency of sdhB-A794G was higher in SDHI-treated vineyards than in vineyards without any SDHI application. A significant difference in the presence of the marker was detected among wine regions; its prevalence ranged from none to 100%. We identified significant co-occurrence of sdhB-A794G with the CYP51-A495T (Y136F) mutation of the CYP51 gene, a known marker of resistance to DMIs. The monitoring of fungicide resistance is fundamental for the successful control of E. necator. Our rapid, cost-effective diagnostic method will support decision-making and fungicide resistance monitoring and management.

Fungicide Use Patterns in Select United States Wine Grape Production Regions

Wine grape production (Vitis sp.) in the United States requires fungicide inputs for disease control. Currently, there is limited data available on vineyard fungicide use patterns. This information is important in developing tailored recommendations for disease management and fungicide stewardship. In this paper, we summarize the wine grape vineyard fungicide use patterns from four major regions: Napa and Sonoma valleys (California), Willamette Valley (Oregon), Columbia Valley (Washington), and several smaller regions east of the Mississippi River in years 2009 to 2020. We learned that the average in-season total fungicide applications ranged regionally from 5.6 to 8. The most commonly applied Fungicide Resistance Action Committee (FRAC) codes in spray programs were FRAC 3, 13, and M02 across all regions, with some variation to the top four groups in each region. Most applications were made on 14-day intervals; however, shorter intervals (7-day) were favored early season, and longer intervals (21-day) were favored late season. Tank-mixing multiple active ingredients was common east of the Mississippi River during all stages of grape development; this action was typically favored during the bloom period in other regions. In a subset of records that participated in FRAC 11 fungicide resistance testing, the average number of FRAC 11 applications after testing was reduced to either no applications or one application in Napa and Sonoma valleys. This survey provides regionally specific data related to fungicide stewardship practices that could be a focus for future stewardship messaging and fungicide resistance selection training, including total product use (selection events), spray intervals (selection pressure), and tank mixing (selection management).[Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Target and non-target site mechanisms of fungicide resistance and their implications for the management of crop pathogens

Fungicides are indispensable for high-quality crops, but the rapid emergence and evolution of fungicide resistance have become the most important issues in modern agriculture. Hence, the sustainability and profitability of agricultural production have been challenged due to the limited number of fungicide chemical classes. Resistance to site-specific fungicides has principally been linked to target and non-target site mechanisms. These mechanisms change the structure or expression level, affecting fungicide efficacy and resulting in different and varying resistance levels. This review provides background information about fungicide resistance mechanisms and their implications for developing anti-resistance strategies in plant pathogens. Here, our purpose was to review changes at the target and non-target sites of quinone outside inhibitor (QoI) fungicides, methyl-benzimidazole carbamate (MBC) fungicides, demethylation inhibitor (DMI) fungicides, and succinate dehydrogenase inhibitor (SDHI) fungicides and to evaluate if they may also be associated with a fitness cost on crop pathogen populations. The current knowledge suggests that understanding fungicide resistance mechanisms can facilitate resistance monitoring and assist in developing anti-resistance strategies and new fungicide molecules to help solve this issue. © 2023 Society of Chemical Industry.

Structure-Based Discovery of New Succinate Dehydrogenase Inhibitors via Scaffold Hopping Strategy

Scaffold hopping strategy has become one of the most successful methods in the process of molecular design. Seeking to develop novel succinate dehydrogenase inhibitors (SDHIs), we employed a scaffold hopping strategy to design compounds featuring geminate dichloralkenes (gem-dichloralkenes) fragment. After stepwise modifications, a series of N-cyclopropyl-dichloralkenes-pyrazole-carboxamide derivatives was synthesized. Among them, compounds G28 (IC50 = 26.00 nM) and G40 (IC50 = 27.00 nM) were identified as the best inhibitory activity against porcine SDH, with IC50 values reaching the nanomolar range, outperforming the lead compound pydiflumetofen. Additionally, the greenhouse assay indicated that compounds G37 (EC90 = 0.031 mg/L) and G34 (EC90 = 1.67 mg/L) displayed extremely high activities against wheat powdery mildew (WPM) and cucumber powdery mildew (CPM), respectively. Computational results further revealed that the gem-dichloralkene fragment and fluorine substituted pyrazole form an extra hydrophobic interaction and dipolar-dipolar interaction with SDH. In summary, our study provides a novel gem-dichloralkene scaffold with outstanding fungicidal properties, obtained through scaffold hopping, that holds great potential for future research on PM control.

Comprehensive analyses of the occurrence of a fungicide resistance marker and the genetic structure in Erysiphe necator populations

Genetically distinct groups of Erysiphe necator, the fungus causing grapevine powdery mildew infect grapevine in Europe, yet the processes sustaining stable genetic differences between those groups are less understood. Genotyping of over 2000 field samples from six wine regions in Hungary collected between 2017 and 2019 was conducted to reveal E. necator genotypes and their possible differentiation. The demethylase inhibitor (DMI) fungicide resistance marker A495T was detected in all wine regions, in 16% of the samples. Its occurrence differed significantly among wine regions and grape cultivars, and sampling years, but it did not differ between DMI-treated and untreated fields. Multilocus sequence analyses of field samples and 59 in vitro maintained isolates revealed significant genetic differences among populations from distinct wine regions. We identified 14 E. necator genotypes, of which eight were previously unknown. In contrast to the previous concept of A and B groups, European E. necator populations should be considered genetically more complex. Isolation by geographic distance, growing season, and host variety influence the genetic structuring of E. necator, which should be considered both during diagnoses and when effective treatments are planned.