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ARS Home » Midwest Area » East Lansing, Michigan » Sugarbeet and Bean Research » Research » Publications at this Location » Publication #392737
Research Project: Genetic Characterization for Sugar Beet Improvement

Location: Sugarbeet and Bean Research

Title: Tracking fungicide resistance and population structure of Erysiphe necator in California table grapes in response to fungicide programs

Author
item Stahr, Madison
item TORRES, GABRIEL - University Of California Agriculture And Natural Resources (UCANR)
item Neill, Tara
item Mahaffee, Walter
item Naegele, Rachel

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 5/15/2021
Publication Date: 1/1/2022
Citation: Stahr, M.N., Torres, G., Neill, T.M., Mahaffee, W.F., Naegele, R.P. 2022. Tracking fungicide resistance and population structure of Erysiphe necator in California table grapes in response to fungicide programs. Phytopathology. 112(11): Abstract #3340. Plant Health 2022-American Phytopathology Society, Pittsburgh, PA, Aug 6-10, 2022.

Interpretive Summary:

Technical Abstract: Powdery mildew, caused by Erysiphe necator, is the most limiting disease for California grape production and is often controlled with fungicide programs that use quinone outside inhibitors (QoI) and demethylation inhibitors (DMI). To determine the seasonal distribution of QoI and DMI fungicide resistance in E. necator isolates on table grape, powdery mildew samples were collected from two ‘Autumn King’ vineyards in San Joaquin Valley, CA between 2019 and 2021. The vineyards were arranged in a complete randomized design with six fungicide programs, including a grower standard program as a control. Sample DNA was extracted using Chelex and screened for QoI resistance using a qPCR assay to detect the G143A mutation. Next, sample DNA was pooled by collection date, field, and treatment for amplicon sequencing. To conduct amplicon sequencing, 28 primer pairs were designed in Primer3, each representing a single copy E. necator gene. Amplified target sequences, ranging from 150 to 300 bp, were checked for SNP presence through BLAST. Primer pairs were then tested against E. necator DNA in single and multiplex reactions. Primer pairs with predicted sequences that lacked SNPs or failed to amplify the intended target in single or multiplex reactions were removed. Overall, the qPCR assay found a shift in both fields over the growing season from primarily QoI sensitive and mixed isolates to QoI resistant isolates. Additionally, 19 primer pairs, arranged in five multiplex reactions, were selected for pooled amplicon sequencing and will be used to assess E. necator population structure.