Schneider R W, Hollier C A, Whitam H K, Palm M E, McKemy J M, Hernández J R, Levy L, DeVries-Paterson R
Department of Plant Pathology and Crop Physiology, Louisiana State University AgCenter, Baton Rouge 70803.
USDA/APHIS/PPQ/NIS, Beltsville, MD 20705.
Plant Dis. 2005 Jul;89(7):774. doi: 10.1094/PD-89-0774A.
Asian soybean rust, caused by Phakopsora pachyrhizi Sydow, has been known to occur in the eastern hemisphere for nearly a century. More recently, it was reported from Hawaii in 1994, eastern and southern Africa from 1996-1998, Nigeria in 2001, and Brazil and Paraguay in 2002. Aerobiological models suggested that urediniospores of the pathogen would be disseminated on wind currents to the continental United States in association with tropical storms if the disease became established north of the equator during hurricane season (U.S. Soybean Rust Detection and Aerobiological Modeling online publication at www.aphis.usda.gov/ppq/ ep/soybean_rust/ ). Since soybean rust was observed at approximately 5°N latitude in South America before several hurricanes impacted the continental United States in September 2004, it seems likely that the introduction was associated with at least one of these tropical storms, especially hurricane Ivan. Symptoms of the disease were first observed on soybean (Glycine max (L.) Merr.) in the continental United States on November 6, 2004 in a field near Baton Rouge, LA. Typical pustules and urediniospores on infected leaves were readily apparent when viewed with a dissecting microscope. Urediniospores were obovoid to broadly ellipsoidal, hyaline to pale yellowish brown with a minutely echinulate thin wall, and measured 18 to 37 × 15 to 24 μm. Paraphyses were cylindric to clavate and slightly thickened at the apex, colorless to pale yellowish brown, and 25-50 × 6-14 μm in size. This morphology is typical of Phakopsora pachyrhizi and P. meibomiae, a less aggressive, western hemisphere species (2). DNA was extracted from leaves containing sori using the Qiagen DNeasy Plant Mini kit. P. pachyrhizi was detected using a real-time polymerase chain reaction (PCR) protocol (1) that differentiates between P. pachyrhizi and P. meibomiae performed in a Cepheid thermocycler with appropriate positive and negative controls. The PCR master mix was modified to include OmniMix beads (Cepheid). The field diagnosis of P. pachyrhizi was confirmed officially by the USDA/APHIS on November 10, 2004, and this was followed on November 11, 2004 by a wide-ranging survey of soybean and kudzu (Pueraria sp.) in soybean production areas in southern and central Louisiana. Collections from this survey also were assayed as described above, and six soybean specimens from five sites were confirmed positive. The disease was not found on kudzu samples. To our knowledge, this is the first report of P. pachyrhizi in the continental United States. Voucher specimens have been placed in the USDA National Fungus Collection. References: (1) R. D. Frederick et al. Phytopathology 92:217, 2002. (2) Y. Ono et al. Mycol. Res. 96:825, 1992.
亚洲大豆锈病由大豆层锈菌（Phakopsora pachyrhizi Sydow）引起，在东半球已存在近一个世纪。最近，1994年在夏威夷、1996 - 1998年在非洲东部和南部、2001年在尼日利亚以及2002年在巴西和巴拉圭均有该病报道。空气生物学模型表明，如果在飓风季节该病在赤道以北地区定殖，病原菌的夏孢子将随气流与热带风暴一起传播到美国大陆（美国大豆锈病检测与空气生物学模型在线出版物，网址为www.aphis.usda.gov/ppq/ep/soybean_rust/ ）。由于在2004年9月几场飓风影响美国大陆之前，在南美洲约北纬5°处观察到了大豆锈病，所以这种引入似乎与至少其中一场热带风暴有关，尤其是飓风伊万。2004年11月6日，在美国路易斯安那州巴吞鲁日附近的一块田地里，首次在大豆（Glycine max (L.) Merr.）上观察到该病症状。用解剖显微镜观察时，感染叶片上典型的疱状突起和夏孢子很容易看到。夏孢子倒卵形至宽椭圆形，透明至浅黄褐色，薄壁有微小的刺状突起，大小为18至37×15至24μm。侧丝圆柱形至棒状，顶端稍增厚，无色至浅黄褐色，大小为25 - 50×6 - 14μm。这种形态是大豆层锈菌和美洲层锈菌（P. meibomiae，一种致病性较弱的西半球物种）的典型特征（2）。使用Qiagen DNeasy植物微型试剂盒从含有孢子堆的叶片中提取DNA。采用一种实时聚合酶链反应（PCR）方法（1）检测大豆层锈菌，该方法能区分大豆层锈菌和美洲层锈菌，在Cepheid热循环仪中进行，并设置适当的阳性和阴性对照。PCR主混合物经修改后包含OmniMix珠子（Cepheid）。2004年11月10日，美国农业部动植物卫生检验局正式确认了田间大豆层锈菌的诊断，随后在2004年11月11日，对路易斯安那州南部和中部大豆产区的大豆和葛藤（Pueraria sp.）进行了广泛调查。该调查采集的样本也按上述方法进行检测，来自五个地点的六个大豆样本被确认为阳性。在葛藤样本中未发现该病。据我们所知，这是大豆层锈菌在美国大陆的首次报道。凭证标本已存放在美国农业部国家真菌收藏库中。参考文献：（1）R. D. Frederick等人，《植物病理学》92:217，2002年。（2）Y. Ono等人，《真菌学研究》96:825，1992年。
