Fonseka D L, Gudmestad N C
Department of Plant Pathology, North Dakota State University, Fargo, ND 58108.
Plant Dis. 2016 Sep;100(9):1848-1857. doi: 10.1094/PDIS-01-16-0116-RE. Epub 2016 Jun 13.
Early blight and brown spot, caused by Alternaria solani and Alternaria alternata, respectively, are important foliar diseases of potato, affecting both tuber yield and quality. Most of the commercial cultivars lack resistance; therefore, the application of foliar fungicides remains a primary disease management strategy. Baseline sensitivities of A. solani to difenoconazole and metconazole (demethylation inhibitors) using mycelial growth assay exhibited similar intrinsic activity against the pathogen with mean EC (the effective concentration at which the fungal growth is inhibited by 50%) values of 0.09 μg/ml. However, the sensitivity of individual baseline A. solani isolates to each fungicide varied substantially, resulting in very low and nonsignificant correlation coefficients among fungicides. Mean EC values for baseline A. alternata isolates in response to difenoconazole and metconazole were 0.14 and 0.26 μg/ml, respectively. The sensitivity of the majority of A. solani and A. alternata isolates collected from 2010 to 2014 from various potato production states was consistent with baseline isolates, therefore, these potato pathogens remain sensitive to the two demethylation inhibitor chemistries used to manage it. Baseline sensitivity assays of pyrimethanil (anilino-pyrimidine) also indicated great intrinsic activity against both foliar pathogens with mean EC values of 0.44 and 0.35 μg/ml for A. solani and A. alternata, respectively. Although A. alternata remains largely sensitive to pyrimethanil, 6 out of 245 A. solani isolates collected from 2010 to 2014 exhibited reduced-sensitivity to the fungicide in in vitro assays. Reduced-sensitive isolates were not controlled at most pyrimethanil doses except at 100 μg/ml in greenhouse in vivo efficacy tests. These chemistries remain valuable options for fungicide rotation programs in areas of high disease pressure.
早疫病和褐斑病分别由茄链格孢和链格孢引起，是马铃薯重要的叶部病害，会影响块茎产量和品质。大多数商业栽培品种缺乏抗性；因此，叶面喷施杀菌剂仍然是主要的病害管理策略。采用菌丝生长法测定茄链格孢对苯醚甲环唑和丙环唑（脱甲基抑制剂）药的基线敏感性，结果显示这两种药剂对该病原菌具有相似的内在活性，平均EC（抑制真菌生长50%的有效浓度）值为0.09μg/ml。然而，各个茄链格孢分离株对每种杀菌剂的敏感性差异很大，导致杀菌剂之间的相关系数非常低且无显著意义。链格孢分离株对苯醚甲环唑和丙环唑的基线平均EC值分别为0.14μg/ml和0.26μg/ml。2010年至2014年从不同马铃薯生产州采集的大多数茄链格孢和链格孢分离株的敏感性与基线分离株一致，因此，这些马铃薯病原菌对用于病害防治的两种脱甲基抑制剂化学药剂仍然敏感。嘧霉胺（苯胺基嘧啶）的基线敏感性测定也表明其对两种叶部病原菌均具有很强的内在活性，茄链格孢和链格孢的平均EC值分别为0.44μg/ml和0.35μg/ml。虽然链格孢对嘧霉胺仍基本敏感，但在2010年至2014年采集的245个茄链格孢分离株中，有6个在体外试验中对该杀菌剂表现出敏感性降低。在温室活体药效试验中，除100μg/ml剂量外，大多数嘧霉胺剂量下对敏感性降低的分离株均无防治效果。在病害压力大的地区，这些化学药剂仍是杀菌剂轮换方案的重要选择。
