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Research Project: Genetic Improvement of Small Grains for Biotic and Abiotic Stress Tolerance and Characterization of Pathogen Populations

Location: Plant Science Research

Title: Evaluating fungicide sensitivity of regional Blumeria graminis f.sp. tritici populations in the United States

Author
item MEYERS, EMILY - North Carolina State University
item Parks, Wesley
item ARELLANO, CONSUELO - North Carolina State University
item Cowger, Christina

Submitted to: American Phytopathological Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/30/2014
Publication Date: N/A
Citation: N/A

Interpretive Summary: The fungus that causes wheat powdery mildew has a high likelihood of developing fungicide resistance, which can then spread to nearby regions because spores are dispersed by air. We are studying whether wheat mildew fungicide sensitivity differs regionally in the United States. In 2013, wheat powdery mildew samples were collected from 11 unsprayed wheat fields in eight states grouped into four regions (Deep South, Mid-Atlantic, Great Lakes, and Plains). The sensitivity of over 150 mildew strains was evaluated by letting them grow individually on leaves of a susceptible wheat variety that has been sprayed with fungicide and grown on agar in a Petri plate. Five fungicides (tebuconazole, prothioconazole, pyraclostrobin, picoxystrobin, and fluxapyroxad) were evaluated at 11 rates each. The lowest fungicide concentration was determined that would keep the mildew strain to a disease rating of 1 on a scale of 0 to 3, with 3 being the most diseased. These concentrations were averaged by field and compared across states and regions. Preliminary results indicate significant regional differences for tebuconazole and prothioconazole, with mildew strains from the Deep South being the least sensitive, Mid-Atlantic and Great Lakes strains moderately sensitive, and Plains strains the most sensitive. Strains from the Plains isolates were least sensitive to pyraclostrobin and fluxapyroxad, while Great Lakes and Deep South strains were moderately sensitive, and Mid-Atlantic isolates the most sensitive to these two products. The sensitivity to picoxystrobin was not significantly different among regions.

Technical Abstract: Blumeria graminis f.sp. tritici (Bgt), cause of wheat powdery mildew, has a high likelihood of developing fungicide resistance because of the large quantity of spores produced along with the mixed mode of reproduction. Additionally, once reduced sensitivity appears in a population it can influence nearby populations because spores are dispersed aerially. This study seeks to determine if fungicide sensitivity in Bgt populations differs regionally in the United States. In 2013, wheat powdery mildew samples were collected from 11 unsprayed wheat fields in eight states grouped into four regions (Deep South, Mid-Atlantic, Great Lakes, and Plains). The sensitivity of over 150 single-spored isolates was evaluated by inoculating them individually on susceptible detached wheat leaves previously sprayed with fungicides and floated on benzimidazole-amended agar. Five fungicides (tebuconazole, prothioconazole, pyraclostrobin, picoxystrobin, and fluxapyroxad) were evaluated at 11 rates each, in ranges chosen based on initial experiments with a small subset of isolates. EC50 values were determined for each field, state, and region using regression and compared using ANOVA. Preliminary partial results indicate significant regional differences for tebuconazole and prothioconazole with Bgt isolates from the Deep South being the least sensitive, Mid-Atlantic and Great Lakes isolates moderately sensitive, and Plains isolates the most sensitive. Interestingly, Plains isolates were least sensitive to pyraclostrobin and fluxapyroxad, Great Lakes and Deep South isolates moderately sensitive, and Mid-Atlantic isolates the most sensitive. The sensitivity to picoxystrobin was not significantly different among regions.