Gaetán S A, Madia M
Cátedra de Fitopatología, Facultad de Agronomía, Universidad de Buenos Aires, Avda. San Martín 4453, 1417, Argentina.
Plant Dis. 2008 Jan;92(1):172. doi: 10.1094/PDIS-92-1-0172B.
Canola (Brassica napus) is a minor rotation crop grown since the 1990s in Buenos Aires Province, Argentina because of its potential as a source of biodiesel. During the spring of 2006, typical signs and symptoms of Sclerotinia stem rot were observed on canola plants (cv. Master) in one production field at 9 de Julio locality in Buenos Airs Province. Affected plants were distributed in patches throughout the rows at flowering and podfilling stages resulting in approximately 7 to 11% plant loss. Initial symptoms consisted of yellowing of mature leaves, decaying, and necrosis of lower stems. Ultimately, crowns and lower stems rotted, stems bleached, pods remained unfilled, and entire plants collapsed. White mycelium and numerous small sclerotia appeared on crown tissues. Samples of 20 infected plants were randomly collected in one production field, and 5- to 10-mm pieces of symptomatic tissues were cultured on potato dextrose agar (PDA) for 7 to 8 days after disinfestation with 2% sodium hypochlorite. Four colonies isolated from symptomatic tissues were identified as Sclerotinia minor Jagger (3) on the basis of white, fluffy mycelium containing black, irregularly shaped sclerotia (≤2 mm in diameter) abundantly scattered over the cultured surface. Crown inoculations were performed for two isolates by placing a plug taken from an actively growing culture of S. minor into wounds made on 6-week-old canola plants (cvs. Eclipse, Master, and Mistral). Control plants received plugs of sterile PDA. Inoculated and control plants were enclosed in plastic bags for 72 h. Symptoms similar to those in the affected fields were evident within 2 weeks of postinoculation on inoculated plants, whereas control plants remained healthy. The pathogen was successfully recovered from infected tissues fulfilling Koch's postulates. The experiment was repeated with similar results. Sclerotinia stem rot caused by S. sclerotiorum (Lib.) de Bary was previously reported on canola in Argentina in 2005 (2), and S. minor is a pathogen of B. napus in the United States (1). To our knowledge, this is the first report of Sclerotinia stem rot of canola incited by S. minor in Argentina. References: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. (2) S. Gaetán and M. Madia. Plant Dis. 89:530, 2005. (3) C. L. Patterson and R. Grogan. Plant Dis. 72:1046, 1988.
油菜（甘蓝型油菜）是自20世纪90年代以来在阿根廷布宜诺斯艾利斯省种植的一种次要轮作作物，因其具有作为生物柴油来源的潜力。2006年春季，在布宜诺斯艾利斯省9 de Julio地区的一个生产田块中，油菜植株（品种Master）上观察到了核盘菌茎腐病的典型症状和体征。受影响的植株在开花期和结荚期整行呈斑块状分布，导致约7%至11%的植株损失。最初的症状包括成熟叶片发黄、腐烂以及下部茎坏死。最终，植株的根茎和下部茎腐烂，茎部变白，荚果未充实，整株植物倒伏。在根茎组织上出现了白色菌丝体和大量小菌核。在一个生产田块中随机采集了20株受感染植株的样本，将5至10毫米的症状组织块用2%次氯酸钠消毒后，在马铃薯葡萄糖琼脂（PDA）上培养7至8天。从症状组织中分离出的四个菌落，根据其白色、蓬松的菌丝体上含有大量散布在培养表面的黑色、形状不规则（直径≤2毫米）的菌核，被鉴定为小核盘菌Jagger（3）。通过将从小核盘菌活跃生长培养物中取出的菌块放入6周龄油菜植株（品种Eclipse、Master和Mistral）上造成的伤口中，对两个分离株进行了根茎接种。对照植株接种无菌PDA菌块。接种和对照植株用塑料袋包裹72小时。接种后2周内，接种植株上出现了与受影响田块中相似的症状，而对照植株保持健康。从受感染组织中成功分离出病原体，满足了柯赫氏法则。该实验重复进行，结果相似。核盘菌（Lib.）de Bary引起的核盘菌茎腐病此前于2005年在阿根廷的油菜上有过报道（2），小核盘菌是美国甘蓝型油菜的一种病原体（1）。据我们所知，这是阿根廷首次关于小核盘菌引起油菜核盘菌茎腐病的报道。参考文献：（1）D. F. Farr等人，《美国植物和植物产品上的真菌》，美国植物病理学会，明尼苏达州圣保罗，1989年。（2）S. Gaetán和M. Madia，《植物病害》89:530，2005年。（3）C. L. Patterson和R. Grogan，《植物病害》72:1046，1988年。
