Phytoparasitica (2008) 36, 136-143

Xiao Zhang, Yu Chen, Zhang Yan-Jun and Ming-Guo Zhou (2008)
Occurrence and molecular characterization of azoxystrobin resistance in cucumber downy mildew in Shandong Province of China
Phytoparasitica 36 (2), 136-143
Abstract: Cucumber downy mildew caused by Pseudoperonospora cubensis (Berk. and Curt.) Rostov. limits crop production in Shandong Province of China. Since management of downy mildew is strongly dependent on fungicides, a rational design of control programs requires a good understanding of the fungicide resistance phenomenon in field populations of the pathogen. A total of 106 and 97 isolates of P. cubensis were obtained in 2006 and 2007, respectively. The EC₅₀ values for the growth of all the 106 isolates collected in 2006 were 0.0063-0.0688 µg ml^-1 (average: 0.0196±0.0048 µg ml^-1) azoxystrobin and these were therefore considered sensitive isolates. However, 57 field isolates of P. cubensis of the 97 collected in 2007 with EC₅₀ values that ranged from 0.609 to >51.2 µg ml^-1 were considered resistant to azoxystrobin. Fragments of the fungicide-targeted mitochondrial cytochrome b gene from total pathogen DNA were amplified using polymerase chain reaction and their sequences analyzed to elucidate the molecular mechanism of resistance. A single point mutation (GGT to GCT) in the cytochrome b gene, resulting in substitution of glycine by alanine at position 143, was found in the three selected azoxystrobin-resistant isolates of downy mildew. This substitution in cytochrome b exhibited different resistance levels, with the resistance factor from 21.15 to greater than 2618.9. In addition, the different resistance levels seemed to appear within 1 year (between 2006 and 2007).Therefore, growers of Shandong Province in China now are faced with a challenge in managing the azoxystrobin resistance in cucumber downy mildew.
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Link to article at publishers website
Database assignments for author(s): Ming-Guo Zhou

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	Cucumber (Cucumis sativus)	China (NE)