Gudmestad N C, Arabiat S, Miller J S, Pasche J S
Department of Plant Pathology, North Dakota State University, Fargo, ND 58108.
Miller Research, 426 East 200 North, Rupert, ID 83350.
Plant Dis. 2013 Jul;97(7):952-960. doi: 10.1094/PDIS-12-12-1176-RE.
Early blight, caused by Alternaria solani, is an important chronic foliar disease of potato (Solanum tuberosum) present every growing season in the Midwestern United States. Most currently grown potato cultivars lack resistance to early blight; therefore, foliar fungicides are relied upon for disease management. Foliar fungicides with high efficacy against the pathogen, such as boscalid, frequently are used under high disease pressure situations, such as potatoes grown under overhead irrigation. Boscalid is a member of the succinate dehydrogenase inhibiting (SDHI) fungicide group and was registered for use on potato in 2005. Baseline sensitivity of A. solani to the SDHI fungicides boscalid, penthiopyrad, and fluopyram using a spore germination assay demonstrated similar intrinsic activity against A. solani with mean EC values of 0.33, 0.38, and 0.31 μg/ml, respectively. However, isolates varied in their sensitivity to each of these fungicides, resulting in very low correlations (r) among isolate sensitivity to each fungicide. Resistance to boscalid in A. solani was detected in the states of North Dakota, Minnesota, Nebraska, Texas, Idaho, Wisconsin, and Florida from early blight samples collected in 2010 and 2011. Two phenotypes of boscalid resistance were detected. Approximately 80% of all A. solani assayed were found to have some level of resistance to boscalid with about 5 and 75% of the population moderately resistant (5 to 20 μg/ml) and highly resistant (>20 μg/ml), respectively, to the fungicide. Nearly 99% of all boscalid resistant isolates possessed the F129L mutation in the cytrochrome b gene, indicating that an A. solani population with dual fungicide resistance predominates in the states surveyed. However, A. solani isolates resistant to boscalid remained sensitive to fluopyram, and a large proportion of moderately resistant and resistant isolates were sensitive to penthiopyrad. Disease control data from in vivo trials demonstrated a significant loss of fungicide efficacy when boscalid and fluxapyroxad were used to control moderately and highly resistant isolates of A. solani relative to the control these fungicides provided wild-type isolates. Fluopyram, however, controlled boscalid resistant isolates as well as it controlled wild-type isolates of A. solani. These data will assist potato growers in regions where boscalid resistance is prevalent by assisting them in avoiding fungicides that do not effectively control early blight and in selecting SDHI fungicide molecules that remain efficacious.
早疫病由链格孢菌引起，是美国中西部每个生长季节都会出现的马铃薯（茄属）重要叶部慢性病。目前种植的大多数马铃薯品种缺乏对早疫病的抗性；因此，叶部杀菌剂被用于病害管理。对病原体具有高效的叶部杀菌剂，如啶酰菌胺，经常在高病害压力情况下使用，比如在顶喷灌溉条件下种植的马铃薯。啶酰菌胺是琥珀酸脱氢酶抑制剂（SDHI）类杀菌剂的一员，于2005年登记用于马铃薯。使用孢子萌发试验测定链格孢菌对SDHI杀菌剂啶酰菌胺、戊唑嘧菌胺和氟吡菌酰胺的基线敏感性，结果表明它们对链格孢菌具有相似的内在活性，平均EC值分别为0.33、0.38和0.31μg/ml。然而，分离株对这些杀菌剂的敏感性各不相同，导致各杀菌剂之间分离株敏感性的相关性非常低（r）。从2010年和2011年采集的早疫病样本中，在北达科他州、明尼苏达州、内布拉斯加州、得克萨斯州、爱达荷州、威斯康星州和佛罗里达州检测到链格孢菌对啶酰菌胺产生抗性。检测到两种啶酰菌胺抗性表型。在所有检测的链格孢菌中，约80%被发现对啶酰菌胺有一定程度的抗性，其中约5%和75%的群体对该杀菌剂中度抗性（5至20μg/ml）和高度抗性（>20μg/ml）。在所有对啶酰菌胺抗性的分离株中，近99%在细胞色素b基因中存在F129L突变，这表明在所调查的州中，具有双重杀菌剂抗性的链格孢菌群体占主导。然而，对啶酰菌胺抗性的链格孢菌分离株仍对氟吡菌酰胺敏感，并且很大比例的中度抗性和抗性分离株对戊唑嘧菌胺敏感。体内试验的病害防治数据表明，当使用啶酰菌胺和氟唑菌酰胺防治链格孢菌的中度和高度抗性分离株时，相对于它们对野生型分离株的防治效果，杀菌剂的效果显著降低。然而，氟吡菌酰胺对啶酰菌胺抗性分离株的防治效果与对链格孢菌野生型分离株的防治效果相同。这些数据将帮助早疫病流行地区的马铃薯种植者避免使用不能有效防治早疫病的杀菌剂，并选择仍然有效的SDHI杀菌剂分子。
