Institute of Botany, University of Basel, Basel, Switzerland.
Pest Manag Sci. 2011 Oct;67(10):1211-4. doi: 10.1002/ps.2238. Epub 2011 Jul 21.
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.
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.
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.
古巴假霜霉（Pseudoperonospora cubensis）是葫芦科作物霜霉病的病原菌，尤其是在黄瓜和甜瓜中，会导致巨大的作物损失。病害防治主要通过寄主抗性和杀菌剂应用的组合来实现。然而，自 2004 年以来，病原菌已克服了黄瓜对霜霉病的抗性，从而迫使农民仅依赖杀菌剂喷雾应用，包括羧酸酰胺（CAA）杀菌剂。最近，回收了对 CAA 具有抗性的古巴假霜霉菌株，但未揭示其抗性的潜在机制。本研究旨在鉴定控制古巴假霜霉菌对 CAA 抗性的分子机制。
鉴定了负责古巴假霜霉菌纤维素生物合成的四个 CesA（纤维素合酶）基因。抗性菌株在 CesA3 基因的 1105 位发生突变，导致甘氨酸突变为缬氨酸或色氨酸。对不同 CAA 的交叉抗性测试表明，这些突变导致对所有测试的 CAA 均具有抗性。
古巴假霜霉菌 CesA3 基因的点突变导致对 CAA 的抗性。对古巴假霜霉菌种群中这些突变的准确监测可能有助于/促进田间适当推荐/部署杀菌剂。
