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ARS Home » Midwest Area » East Lansing, Michigan » Sugarbeet and Bean Research » Research » Publications at this Location » Publication #305756
Title: Fungicide sensitivity testing of Cercospora beticola from sugarbeet in the Great Lakes Region

Author
item JIANG, QIANWEI - Michigan State University
item KIRK, WILLIAM - Michigan State University
item ROSENZWEIG, NOAH - Michigan State University
item SOMOHANO, PAULA - Michigan State University
item Hanson, Linda

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2014
Publication Date: 11/1/2014
Citation: Jiang, Q., Kirk, W.W., Rosenzweig, N., Somohano, P., Hanson, L.E. 2014. Fungicide sensitivity testing of Cercospora beticola from sugarbeet in the Great Lakes Region [abstract]. Phytopathology. 104:S3.55.

Interpretive Summary:

Technical Abstract: Cercospora leaf spot (CLS), caused by Cercospora beticola (Sacc.), is the most serious foliar disease of sugarbeet (Beta vulgaris L.) worldwide. CLS is problematic in most sugarbeet growing regions and can cause significant economic losses due to decreases in both yield and sugar purity in the harvested roots. Among all the management strategies, timely and effective fungicide application is one of the most effective management tools. However, resistance has been reported in popualtions of C. beticola to several classes of fungicides including benzimidazoles, organo-tins and demethylation inhibitors (DMIs). In 2011, quinine outside inhibitor (QoI)-tolerance was identified in Michigan, and later in other areas. A spiral gradient method (SDG) to estimate the fungicide concentration that causes a 50% inhibition of spore germination or mycelial growth (EC50) was used to examine sensitivity to QoIs and benzimidazoles, respectively. Nearly 90% of isolates tested were insensitive to thiophanate-methyl, indicating an increase from about 50% observed from 2002-2011. In 2012, out of forty-nine isolates tested for pyraclostrobin response with SDG, 71% had EC50 values greater than 64 ppm. A similar ratio was found using sequencing of PCR products with 25 out of 32 having 100% identity with the sequenced QoI-resistant C. beticola. Testing isolates of C. beticola for resistance to the major remaining classes of fungicides was continued in 2013. The majority of the isolates were sensitive to organo-tin and demethylation inhibitors with EC50 values less than 1.0 ppm. Additional tests of fungicide sensitivity to benzimidazole and QoI fungicides of C. beticola using PCR-RFLP analysis are ongoing.