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POSTERS: Fungicide and antibiotic resistance

A high throughput bioassay to rapidly characterize Erysiphe necator resistance to demethylation inhibitor fungicides
Alexander Wong - Oregon State Univeristy. Walter Mahaffee- USDA ARS

Fungicide resistance of Erysiphe necator to demethylation inhibitor (DMI, FRAC 3) and Quinone outside oxidase inhibitor fungicides is widespread in the Western US E. necator populations, increasing resistance pressure on more modern fungicide chemistries. Currently, resistance to DMI fungicides can only be detected using time and resource expensive live leaf assays because resistance to DMIs is quantitative and the genetic control is not fully understood. We hypothesize that the conidium does not contain enough metabolic precursors to synthesize the sterol, ergosterol, before having to synthesize de novo; thus, fungicide resistance will be expressed as increased germination tube development on fungicide amended matrix. Erysiphe necator conidia were dispersed onto a 24-well plate with fungicide amended gellan gum medium and imaged immediately, and again after 24 hours to measure the development and elongation of germination tubes. The images were processed in ImageJ using the “HyphaTracker” macro. The percent change in the germination tube growth from the untreated control over 24 hours was measured for each concentration of the fungicide. At 3 µg/ml active ingredient, sensitive isolates germination tube development is reduced by at least 50%. This method can objectively assess 4 to 5 isolates with only 3-4 hours of labor and a 24-hour incubation period, as compared to leaf disks bioassays, which require 12 hours of labor, a 14-day incubation.