University of Florida, Gulf Coast Research and Education Center, Wimauma, FL 33598.
Plant Dis. 2020 Apr;104(4):1224-1230. doi: 10.1094/PDIS-06-19-1140-RE. Epub 2020 Feb 20.
Succinate dehydrogenase inhibitors (SDHIs) are the fungicides most commonly used to control Botrytis fruit rot on commercial strawberry in Florida. The medium-to-high risk of selection of resistance in the causal agent is a threat to the efficacy of this fungicide group. In this study, we characterized the sensitivity of to the SDHI isofetamid, evaluated the SdhB gene mutation associated with resistance, and monitored resistance frequencies to five SDHI fungicides for two consecutive seasons. EC values of 70 isolates were obtained using the spiral gradient dilution (SGD) method and averaged 0.098 µg/ml of isofetamid. EC averages of 3.04 and >500.00 µg/ml were obtained for isolates with the N230I and P225F mutations indicating moderate and high resistance to isofetamid, respectively. A total of 565 isolates collected during 2015-2016 and 2016-2017 seasons from strawberry nurseries and Florida production fields were evaluated using conidial germination assays. Results for the first season showed resistance frequencies of 95, 33, 21, 25, and 0% to boscalid, penthiopyrad, fluopyram, benzovindiflupyr, and isofetamid, respectively. The respective resistance frequencies for the following season were 91, 95, 44, 27, and 1.3%. Only three isolates were found to be moderately resistant to isofetamid during the second season, and the mutation N230I was identified after sequence analysis. These isolates were confirmed to be resistant to isofetamid in fruit assays with disease incidence of 55.6 to 77.0%; however, the conidial production of the isolates was inhibited by an average of 83.9%. In general, isofetamid efficacy was higher than the other evaluated SDHIs, but a slight increase in resistance frequencies was observed in our study.
琥珀酸脱氢酶抑制剂（SDHIs）是佛罗里达州用于防治商业草莓灰霉病的最常用杀菌剂。病原菌对该杀菌剂的中等至高风险选择是对该杀菌剂的有效性的威胁。在这项研究中，我们对 对 SDHI 异恶唑酰胺的敏感性进行了特征描述，评估了与抗性相关的 SdhB 基因突变，并连续两个季节监测了对五种 SDHI 杀菌剂的抗性频率。使用螺旋梯度稀释（SGD）方法获得了 70 个分离物的 EC 值，异恶唑酰胺的平均 EC 值为 0.098 µg/ml。具有 N230I 和 P225F 突变的分离物的 EC 平均值分别为 3.04 和>500.00 µg/ml，表明对异恶唑酰胺具有中等和高度抗性。2015-2016 年和 2016-2017 年从草莓苗圃和佛罗里达州生产田收集的共 565 个分离物使用孢子萌发测定法进行了评估。第一个季节的结果显示，对 boscalid、penthiopyrad、fluopyram、benzovindiflupyr 和 isofetamid 的抗性频率分别为 95、33、21、25 和 0%。下一季的相应抗性频率分别为 91、95、44、27 和 1.3%。第二个季节仅发现三个分离物对异恶唑酰胺具有中度抗性，并且在序列分析后鉴定出突变 N230I。这些分离物在果实测定中被确认为对异恶唑酰胺具有抗性，发病率为 55.6%至 77.0%；然而，分离物的分生孢子产生被平均抑制了 83.9%。一般来说，异恶唑酰胺的功效高于其他评估的 SDHIs，但在我们的研究中观察到抗性频率略有增加。
