Bradley C A, Hines R A, Pataky N R, Haudenshield J S, Hartman G L
Department of Crop Sciences, University of Illinois, Urbana 61801.
United States Department of Agriculture-Agricultural Research Service, Urbana, IL 61801.
Plant Dis. 2010 Apr;94(4):477. doi: 10.1094/PDIS-94-4-0477A.
Soybean rust, caused by Phakopsora pachyrhizi Syd., first was observed in the continental United States during 2004 on soybean (Glycine max (L.) Merr.) in Louisiana (4), and on kudzu (Pueraria montana (Lour.) Merr. var. lobata (Willd.) Maesen & Almeida) in Florida (2). Kudzu is a leguminous weed that is prevalent in the southern United States with its range extending northward into other states including Illinois. In October 2009, a kudzu patch located in Pulaski County in southern Illinois was investigated for the presence of soybean rust. Twenty-five leaflets were collected, and the abaxial sides of leaflets were evaluated visually for the presence of uredinia with a dissecting microscope. Uredinia and urediniospores were found on two leaflets. When viewed with a compound microscope, urediniospores were hyaline, echinulate, and measured 20 × 25 μm. On the basis of uredinia and urediniospores, the disease tentatively was identified as soybean rust caused by P. pachyrhizi. To confirm the identification, one leaflet with pustules was assayed with a Soybean Rust QuickStix Diagnostic Kit (Envirologix, Portland, ME). For the other leaflet, the area of the pustule was excised (approximately 28 mm) and an area of the leaflet at the margin on the opposite half of the leaflet with no visible pustule (approximately 54 mm) was excised. DNA was extracted from the excised areas of the leaflet for confirmation by quantitative PCR (Q-PCR) using primers and probe specific to P. pachyrhizi and P. meibomiae (Arthur) Arthur (1). Both the QuickStix Diagnostic Kit and the Q-PCR confirmed the diagnosis as soybean rust caused by P. pachyrhizi. Q-PCR also suggested the presence of a nonsporulating latent rust infection on the same kudzu leaflet at the margin on the opposite side of the midrib. Soybean rust first was confirmed on soybean in Illinois in 2006 (3), but to our knowledge, this is the first observation of the disease on kudzu in the state. This report confirms that at least some kudzu plants in Illinois are susceptible to soybean rust and that latent kudzu infection may exist without outward signs of the fungus. Currently, this is the most northern observation of soybean rust on kudzu in North America. It is unknown what role, if any, Illinois kudzu will play in the epidemiology of soybean rust in the state. Since kudzu tops die after the first frost, there is no expectation of P. pachyrhizi to overwinter in Illinois on kudzu as it does in some states adjacent to the Gulf of Mexico. References: (1) R. D. Frederick et al. Phytopathology 92:217, 2002. (2) P. F. Harmon et al. Online publication. doi:10.1094/PHP-2005-0613-01-RS. Plant Health Progress, 2005. (3) G. L. Hartman et al. Plant Dis. 91:466, 2007. (4) R. W. Schneider et al. Plant Dis. 89:774, 2005.
大豆锈病由大豆层锈菌（Phakopsora pachyrhizi Syd.）引起，2004年首次在美国大陆被发现，在路易斯安那州的大豆（Glycine max (L.) Merr.）上（4），以及在佛罗里达州的葛藤（Pueraria montana (Lour.) Merr. var. lobata (Willd.) Maesen & Almeida）上（2）。葛藤是一种豆科杂草，在美国南部很常见，其分布范围向北延伸到包括伊利诺伊州在内的其他州。2009年10月，对伊利诺伊州南部普拉斯基县的一片葛藤进行了大豆锈病调查。采集了25片小叶，用解剖显微镜目视评估小叶背面是否存在夏孢子堆。在两片小叶上发现了夏孢子堆和夏孢子。用复式显微镜观察时，夏孢子无色透明，有刺，大小为20×25微米。根据夏孢子堆和夏孢子，初步将该病鉴定为由大豆层锈菌引起的大豆锈病。为了确认鉴定结果，用大豆锈病快速检测试剂盒（Envirologix，缅因州波特兰）对一片有脓疱的小叶进行了检测。对于另一片小叶，切除脓疱区域（约28毫米），并在小叶相对的另一半边缘没有可见脓疱的区域切除一片小叶组织（约54毫米）。从切除的小叶区域提取DNA，使用针对大豆层锈菌和梅氏层锈菌（Phakopsora meibomiae (Arthur) Arthur）的引物和探针通过定量PCR（Q-PCR）进行确认（1）。快速检测试剂盒和Q-PCR均确认诊断为大豆层锈菌引起的大豆锈病。Q-PCR还表明在中脉另一侧边缘的同一片葛藤小叶上存在无孢子的潜伏锈病感染。大豆锈病于2006年首次在伊利诺伊州的大豆上得到确认（3），但据我们所知，这是该州首次在葛藤上观察到这种病害。本报告证实，伊利诺伊州至少一些葛藤植株对大豆锈病易感，并且可能存在葛藤潜伏感染而无真菌的外部迹象。目前，这是北美对葛藤上大豆锈病最北的观察记录。尚不清楚伊利诺伊州的葛藤在该州大豆锈病的流行病学中会起什么作用（如果有作用的话）。由于葛藤顶部在初霜后死亡，预计大豆层锈菌不会像在墨西哥湾附近的一些州那样在伊利诺伊州的葛藤上过冬。参考文献：（1）R. D. Frederick等人，《植物病理学》92:217，2002年。（2）P. F. Harmon等人，在线出版物。doi:10.1094/PHP - 2005 - 0613 - 01 - RS。《植物健康进展》，2005年。（3）G. L. Hartman等人，《植物病害》91:466，2007年。（4）R. W. Schneider等人，《植物病害》89:774，2005年。
