Gent David H, Nelson Mark E, Grove Gary G
United States Department of Agriculture-Agricultural Research Service, Forage Seed and Cereal Research Unit, and Oregon State University, Department of Botany and Plant Pathology, Corvallis 97331.
Department of Plant Pathology, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser 99350.
Plant Dis. 2008 Mar;92(3):463-468. doi: 10.1094/PDIS-92-3-0463.
Downy mildew, caused by Pseudoperonospora humuli, is an important disease of hop in most production regions in the northern hemisphere. Insensitivity to phenylamide fungicides was detected in isolates of P. humuli in production regions in Oregon and Idaho in 1992, and these fungicides since have been used on a limited basis. In this study, the prevalence of phenylamide insensitivity among isolates of P. humuli collected from 2005 to 2007 in the northwestern United States was quantified using a leaf disk assay with a discriminating dose (25 μg/ml) of either metalaxyl or mefenoxam with inoculum derived from 201 systemically infected diseased shoots (basal spikes) collected from 6, 10, and 11 hop yards in Idaho, Washington, and Oregon, respectively. A subset of 47 basal spike isolates and 42 monosporic isolates collected from two yards in Idaho and nine yards in Oregon during 2006 and 2007 were assayed using a dilution series of metalaxyl to determine the effective dose that inhibited 50% of the incidence of sporulation (ED). Insensitivity to mefenoxam was detected in 31 of 74 (41.9%) basal spikes collected from 13 hop yards. Insensitivity to the related compound metalaxyl was detected in 52 of 80 (65%) spikes collected from nine hop yards, including four hop yards in Washington. Log ED values ranged from -2.25 to 2.67 for basal spike isolates and -2.27 to 2.98 for monosporic isolates and had a similar distribution. Log ED values for monosporic isolates and entire basal spike isolates were significantly associated. However, the slope of the regression line was less than 1, indicating that the log ED values obtained from entire basal spike isolates were greater than the corresponding log ED values obtained from a monosporic isolate obtained from that spike. This research suggests that insensitivity to phenylamide fungicides is a stable phenotype in P. humuli. Management of downy mildew should rely on measures other than these fungicides in yards or regions where phenylamide insensitivity is prevalent, which is now known to include certain hop yards in Idaho, Oregon, and Washington.
由葎草假霜霉（Pseudoperonospora humuli）引起的霜霉病是北半球大多数产区啤酒花的一种重要病害。1992年在俄勒冈州和爱达荷州的产区，在葎草假霜霉分离株中检测到对苯酰胺类杀菌剂不敏感，此后这些杀菌剂的使用受到限制。在本研究中，使用叶盘试验，采用甲霜灵或精甲霜灵的鉴别剂量（25μg/ml），对2005年至2007年从美国西北部采集的葎草假霜霉分离株中苯酰胺不敏感性的流行情况进行了量化，接种物来自分别从爱达荷州、华盛顿州和俄勒冈州的6个、10个和11个啤酒花种植园采集的201个系统感染的病枝（基部穗）。2006年和2007年期间，从爱达荷州的两个种植园和俄勒冈州的九个种植园采集的47个基部穗分离株和42个单孢分离株的一个子集，使用甲霜灵的稀释系列进行测定，以确定抑制50%孢子形成发生率的有效剂量（ED）。在从13个啤酒花种植园采集的74个基部穗中的31个（41.9%）中检测到对精甲霜灵不敏感。在从包括华盛顿州的四个啤酒花种植园在内的九个啤酒花种植园采集的80个穗中的52个（65%）中检测到对相关化合物甲霜灵不敏感。基部穗分离株的对数ED值范围为-2.25至2.67，单孢分离株的对数ED值范围为-2.27至2.98，且分布相似。单孢分离株和整个基部穗分离株的对数ED值显著相关。然而，回归线的斜率小于1，表明从整个基部穗分离株获得的对数ED值大于从该穗获得的单孢分离株的相应对数ED值。本研究表明，对苯酰胺类杀菌剂不敏感是葎草假霜霉中的一种稳定表型。在苯酰胺不敏感普遍存在的种植园或地区，霜霉病的管理应依靠这些杀菌剂以外的措施，现在已知爱达荷州、俄勒冈州和华盛顿州的某些啤酒花种植园存在这种情况。
