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.
