Rosenzweig N, Atallah Z K, Olaya G, Stevenson W R
Department of Plant Pathology, University of Wisconsin, Madison 53706.
Syngenta Crop Protection Inc., Vero Beach Research Center, Vero Beach, FL 32967.
Plant Dis. 2008 Apr;92(4):561-568. doi: 10.1094/PDIS-92-4-0561.
Potato early blight (Alternaria solani) is a yield-limiting disease and control depends primarily on multiple fungicide applications. Azoxystrobin, registered in the United States in 1999, initially provided outstanding early blight control. Within 3 years, approximately 80% of the total potato acreage was being treated with azoxystrobin and other quinone outside inhibitor (QoI), fungicides registered subsequently. Alternaria solani isolates with decreased in vitro sensitivity to azoxystrobin were detected in Wisconsin during 2001. Field experiments were conducted in 2001 to 2003 to evaluate season-long fungicide programs and test fungicide resistance management strategies. The fungicide program recommended to growers at that time, which consisted of three applications of azoxystrobin for weeks 1, 3, and 5 alternated with applications of chlorothalonil at label recommended rates, was effective in controlling early blight when conditions were conducive to disease development. Mean sensitivity in vitro of A. solani isolates from fungicide efficacy field experiments in 2001 to 2003 was numerically highest for isolates from the untreated control plots, chlorothalonil-alone plots, or plots treated with three applications of azoxystrobin alternated with chlorothalonil compared with other treatments tested. Three single-nucleotide polymorphisms (SNPs) can cause the F129L substitution (TTC to TTA, CTC, or TTG) that results in decreased sensitivity to azoxystrobin of A. solani. The TTA mutant was the most frequently recovered mutant type in the field experiments. The frequency of recovery of wild-type isolates in experiments was 22% in 2001, 4% in 2002, and 22% in 2003.
马铃薯早疫病（链格孢菌）是一种限制产量的病害，防治主要依赖多次施用杀菌剂。嘧菌酯于1999年在美国注册，最初对早疫病有出色的防治效果。3年内，约80%的马铃薯种植面积都使用了嘧菌酯及随后注册的其他醌外抑制剂（QoI）类杀菌剂进行处理。2001年在威斯康星州检测到对嘧菌酯体外敏感性降低的链格孢菌分离株。在2001年至2003年进行了田间试验，以评估整个生长季的杀菌剂方案并测试杀菌剂抗性管理策略。当时向种植者推荐的杀菌剂方案，包括在第1、3和5周施用三次嘧菌酯，并与按标签推荐剂量施用的百菌清交替使用，在有利于病害发展的条件下对早疫病防治有效。与其他测试处理相比，2001年至2003年杀菌剂药效田间试验中链格孢菌分离株的体外平均敏感性，在未处理对照地块、仅使用百菌清的地块或用三次嘧菌酯与百菌清交替处理的地块中数值最高。三个单核苷酸多态性（SNP）可导致F129L替换（TTC变为TTA、CTC或TTG），从而使链格孢菌对嘧菌酯的敏感性降低。TTA突变体是田间试验中最常回收的突变类型。在试验中野生型分离株的回收频率在2001年为22%；2002年为4%；2003年为22%。
