Gevens A J, Seidl A C
Department of Plant Pathology, University of Wisconsin, Madison, WI 53706.
Plant Dis. 2013 Mar;97(3):423. doi: 10.1094/PDIS-08-12-0807-PDN.
Tomato (Solanum lycopersicum) and potato (S. tuberosum) crops are grown on over 67,000 acres (27,114 hectares) in the state of Wisconsin each year. Late blight, caused by Phytophthora infestans (Mont.) deBary, is a potentially devastating oomycete pathogen that sporadically affects tomato and potato crops in the state. Prevention of this disease through prophylactic application of oomycete-specific fungicides can cost producers millions of dollars per year in additional chemical, fuel, and labor expenses. In 2009, late blight was observed on tomato and potato in over 25 Wisconsin counties. The epidemic initiated on tomato in southern WI in early August and progressed northward in the state with additional reports on tomato primarily from home gardens and small farms. Potato late blight was also identified but with limited incidence in central WI, likely due to routine fungicide programs in commercial production. Clonal lineages of P. infestans documented in Wisconsin in previous epidemics included US-1 in the 1970s and US-8 in the mid-1990s. Populations of P. infestans in the U.S. have recently undergone significant genetic changes, resulting in isolates with unique clonal lineages and epidemiological characteristics (1). Symptoms of late blight observed on tomato and potato included water-soaked to dark brown circular lesions with pale green haloes accompanied by signs of pathogen sporulation typically on leaf undersides during periods of high humidity. Isolates of P. infestans were generated from field infected tomato and potato foliar tissues. Axenic, single zoospore derived cultures were generated and maintained on Rye A agar for further characterization. Mycelium was coenocytic with hyphal diameter of 5 to 8 μm (n = 50). Sporangia were limoniform or ovoid, semi- to fully papillate, caducous, had short pedicels, and were 29.6 (h) × 16.8 μm (w) (n = 50). The average length/width ratio was 1.76. Allozyme banding patterns at the glucose-6-phosphate isomerase (Gpi) locus indicated a 100/122 profile, consistent with the US-22 clonal lineage (3). Mating type assays confirmed the isolates to be A2 and in vitro mefenoxam sensitivity was observed (4). Restriction fragment length polymorphic analysis of a representative isolate from Wisconsin with the multilocus RG57 sequence and EcoRI produced the DNA pattern indicative of US-22 (2). The P. infestans clonal lineage US-22 was predominant in U.S. epidemics on tomato in 2009. To our knowledge, this is the first report of P. infestans clonal lineage US-22 causing late blight on tomato and potato in Wisconsin, USA. References: (1) K. Deahl. (Abstr.) Phytopathology 100(suppl.):S161, 2010. (2) S. B. Goodwin et al. Curr. Genet. 22:107, 1992. (3) C. H. Hu et al. Plant Dis. 96:1323, 2012. (4) A. C. Seidl et al. Phytopathology 101(suppl.):S246, 2011.
每年，威斯康星州种植番茄（茄属番茄）和马铃薯（茄属马铃薯）的面积超过67000英亩（27114公顷）。由致病疫霉（蒙氏）德巴里引起的晚疫病是一种具有潜在毁灭性的卵菌病原体，偶尔会影响该州的番茄和马铃薯作物。通过预防性施用针对卵菌的杀菌剂来预防这种疾病，每年会使生产者在额外的化学品、燃料和劳动力费用上花费数百万美元。2009年，威斯康星州超过25个县的番茄和马铃薯上观察到了晚疫病。疫情于8月初在威斯康星州南部的番茄上开始，并在该州向北蔓延，关于番茄的更多报告主要来自家庭菜园和小农场。马铃薯晚疫病也被发现，但在威斯康星州中部发病率有限，这可能是由于商业生产中的常规杀菌剂方案。此前疫情中在威斯康星州记录的致病疫霉克隆谱系包括20世纪70年代的US-1和90年代中期的US-8。美国的致病疫霉种群最近发生了重大的遗传变化，导致分离株具有独特的克隆谱系和流行病学特征（1）。在番茄和马铃薯上观察到的晚疫病症状包括水渍状至深褐色的圆形病斑，带有浅绿色晕圈，在高湿度时期通常在叶背面伴有病原体产孢迹象。致病疫霉分离株从田间感染的番茄和马铃薯叶片组织中获得。产生了无菌的、单游动孢子衍生的培养物，并在黑麦A琼脂上进行培养以进行进一步鉴定。菌丝体是多核的，菌丝直径为5至8μm（n = 50）。孢子囊呈柠檬形或卵形，半乳头状至全乳头状，易脱落，有短梗，大小为29.6（高）×16.8μm（宽）（n = 50）。平均长宽比为1.76。葡萄糖-6-磷酸异构酶（Gpi）位点的等位酶带型显示为100/122谱型，与US-22克隆谱系一致（3）。交配型测定证实分离株为A2型，并观察到其对甲霜灵的体外敏感性（4）。用多位点RG57序列和EcoRI对来自威斯康星州的一个代表性分离株进行限制性片段长度多态性分析，产生了指示US-22的DNA模式（2）。致病疫霉克隆谱系US-22在2009年美国番茄疫情中占主导地位。据我们所知，这是致病疫霉克隆谱系US-22在美国威斯康星州导致番茄和马铃薯晚疫病的首次报道。参考文献：（1）K. Deahl。（摘要）植物病理学100（增刊）：S161，2010。（2）S. B. Goodwin等人。当代遗传学22：107，1992。（3）C. H. Hu等人。植物病害96：1323，2012。（4）A. C. Seidl等人。植物病理学101（增刊）：S246，2011。
