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United States Department of Agriculture

Agricultural Research Service

Research Project: ENHANCING PATHOGEN DETECTION AND CROP PROTECTION IN SUGARBEET USING MOLECULAR TECHNOLOGIES

Location: Sugarbeet and Potato Research

Title: PCR-based detection of fungicide resistance in Cercospora beticola

Authors
item Bolton, Melvin
item Secor, Gary -
item Khan, Mohamed -

Submitted to: Sugarbeet Research and Extension Reports
Publication Type: Proceedings
Publication Acceptance Date: February 14, 2011
Publication Date: March 14, 2011
Citation: Bolton, M.D., Secor, G., Khan, M.F. 2011. PCR-based detection of fungicide resistance in Cercospora beticola. 2010 Sugarbeet Research and Extension Reports. 41:229-230. Available: http://www.sbreb.org/research/plant/plant10/BoltenPCRBasedCB2010.pdf.

Interpretive Summary: Leaf spot, caused by the fungus Cercospora beticola, is an endemic disease of sugarbeets in the North Dakota and Minnesota growing regions. Control measures against the fungus include resistant sugarbeet varieties and crop rotation, but the disease is managed effectively only when combined with timely fungicide applications. The development of fungicide-resistance has been closely monitored in C. beticola, and results from sensitivity testing have shown that the North Dakota and Minnesota C. beticola populations have the ability to adapt and become less sensitive to fungicides in relatively short periods of time. Resistance to site-specific fungicides can be due to mutations in a single gene. Resistance to DMI fungicides has been shown to relate either to specific mutations in the CYP51 gene or over-expression of the CYP51 gene leading to an over-production of the target enzyme. The full-length CYP51 gene was cloned from C. beticola and the sequence was analyzed from 25 DMI-sensitive and 25 DMI-resistant isolates. No mutations correlated with reduced sensitivity to DMI fungicides. The Cyp51 gene was analyzed for expression and it was found that resistant isolates have increased expression of this gene.

Technical Abstract: Leaf spot, caused by the fungus Cercospora beticola, is an endemic disease of sugarbeets in the North Dakota and Minnesota growing regions. Control measures against the fungus include resistant sugarbeet varieties and crop rotation, but the disease is managed effectively only when combined with timely fungicide applications. However, C. beticola is well-known for the ability to develop resistance to fungicides of several chemical classes. Resistance to site-specific fungicides can be due to mutations in a single gene. Resistance to DMI fungicides has been shown to relate either to specific mutations in the CYP51 gene, which causes decreased affinity of DMIs to the target enzyme, or over-expression of the CYP51 gene leading to an over-production of the target enzyme. The full-length CYP51 gene was cloned from C. beticola, including several hundred bp on both sides of the gene, for a total of over 2400 bp of derived sequenced. The CYP51 gene was sequenced in 25 DMI-sensitive and 25 DMI-resistant isolates. Several mutations were found in the promoter and coding sequence of the gene. However, in each case, mutations either could not be found in all resistant isolates or some sensitive isolates also harbored the mutation. Gene expression of the CYP51 gene was assessed in in vitro grown cultures. Resistant isolates had a two-to-three-fold increase in CYP51 gene expression.

Last Modified: 4/18/2014
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