Delta Research and Extension Center, Mississippi State University, Stoneville, MS 38776.
Valent U.S.A. LLC, Leland, MS 38756.
Plant Dis. 2023 Aug;107(8):2365-2374. doi: 10.1094/PDIS-06-22-1297-RE. Epub 2023 Aug 18.
Target spot, caused by , is a common lower canopy soybean disease in the southern United States. Recently, target spot has resurged in importance especially following the identification of resistance to the quinone outside inhibitor (QoI) fungicides. As a result, a survey of from soybean throughout Mississippi began in 2018. A total of 819 monoconidial isolates were obtained from 228 fields in 75 counties. The molecular mechanism of QoI resistance was determined, which resulted from an amino acid substitution from glycine (G) to alanine (A) at position 143 using a PCR-RFLP method and comparing nucleotide sequences of the cytochrome gene. Five previously defined geographic regions were used to present the distribution of the G143A substitution and included the Capital, Coast, Delta, Hills, and Pines. The Capital had the greatest proportion of G143A-containing isolates (95.0%), followed by the Coast (92.9%), Delta (89.8%), Pines (78.8%), and Hills (69.4%). In all, 85.8% of the isolates carried the G143A substitution. In addition, the effective fungicide concentration (EC) of randomly selected isolates to azoxystrobin was used to characterize isolates as resistant ( = 14) (based on the presence of the G143A substitution and EC values >52 μg/ml) or sensitive ( = 11) (based on the absence of the G143A substitution and EC values <46 μg/ml). The EC values varied among isolates ( < 0.0001), with QoI-sensitive isolates exhibiting lower EC values than QoI-resistant isolates. The current study revealed that a reduction in sensitivity to QoI fungicides has likely resulted based on the percentage of isolates containing the G143A substitution identified in Mississippi.
靶斑病由引起，是美国南部常见的大豆下部冠层病害。最近，靶斑病的重要性再次凸显，尤其是在鉴定出对醌外抑制剂（QoI）杀菌剂的抗性之后。因此，2018 年开始对密西西比州的大豆进行了调查。从 75 个县的 228 个田间共获得了 819 个单孢分离物。采用 PCR-RFLP 方法，通过比较细胞色素基因的核苷酸序列，确定了 QoI 抗性的分子机制，该机制是由于第 143 位的甘氨酸（G）突变为丙氨酸（A）所致。使用了五个先前定义的地理区域来表示 G143A 取代的分布，包括首都、海岸、三角洲、丘陵和松林。首都地区含有 G143A 分离物的比例最高（95.0%），其次是海岸（92.9%）、三角洲（89.8%）、松林（78.8%）和丘陵（69.4%）。总的来说，85.8%的分离物携带 G143A 取代。此外，还使用随机选择的分离物对唑菌胺酯的有效杀菌剂浓度（EC）来表征分离物的抗性（=14）（基于存在 G143A 取代和 EC 值>52μg/ml）或敏感性（=11）（基于不存在 G143A 取代和 EC 值<46μg/ml）。分离物之间的 EC 值存在差异（<0.0001），QoI 敏感分离物的 EC 值低于 QoI 抗性分离物。本研究表明，基于在密西西比州鉴定出的含有 G143A 取代的分离物的百分比，可能导致对 QoI 杀菌剂的敏感性降低。
