Pest Management Science (2011) 67, 1211-1214

Mathias Blum, Maya Waldner, Gilberto Olaya, Yigal Cohen, Ulrich Gisi and Helge Sierotzki (2011)
Resistance mechanism to carboxylic acid amide fungicides in the cucurbit downy mildew pathogen Pseudoperonospora cubensis
Pest Management Science 67 (10), 1211-1214
Abstract: BACKGROUND: Pseudoperonospora cubensis, the causal oomycete agent of cucurbit downy mildew, is responsible for enormous crop losses in many species of Cucurbitaceae, particularly in cucumber and melon. Disease control is mainly achieved by combinations of host resistance and fungicide applications. However, since 2004, resistance to downy mildew in cucumber has been overcome by the pathogen, thus driving farmers to rely only on fungicide spray applications, including carboxylic acid amide (CAA) fungicides. Recently, CAA-resistant isolates of P. cubensis were recovered, but the underlying mechanism of resistance was not revealed. The purpose of the present study was to identify the molecular mechanism controlling resistance to CAAs in P. cubensis.
RESULTS: The four CesA (cellulose synthase) genes responsible for cellulose biosynthesis in P. cubensis were characterised. Resistant strains showed a mutation in the CesA3 gene, at position 1105, leading to an amino acid exchange from glycine to valine or tryptophan. Cross-resistance tests with different CAAs indicated that these mutations lead to resistance against all tested CAAs.
CONCLUSION: Point mutations in the CesA3 gene of P. cubensis lead to CAA resistance. Accurate monitoring of these mutations among P. cubensis populations may improve/facilitate adequate recommendation/deployment of fungicides in the field.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): Mathias Blum, Yigal R. Cohen, Ulrich Gisi, Helge Sierotzki

Research topic(s) for pests/diseases/weeds:
pesticide resistance of pest

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Pseudoperonospora cubensis