Hema Kasinathan Thesis May 1 2012.pdf - Atrium - University of ...

1 CHAPTER 1LITERATURE REVIEW1.1 ImportancePlasmodiophora brassicae Woronin is a soil-borne biotrophic plant pathogen. Itcauses clubroot in cruciferous crops including canola (Brassica napus L. and B. rapa L.),an economically important oilseed crop, and many Brassica vegetables. The pathogencauses abnormal swelling in root tissues that result in characteristic club-like symptoms.As a result of the hypertrophy and hyperplasia that causesthis swelling, the transport ofwater and mineral nutrients is inhibited, which can result in symptoms such as stunting,wilting, and even premature death (Cao et al. 2009, Strelkov et al. 2005). The pathogencan cause 100% yield loss in fields of severely infested canola (Dixon 2006, Strelkov etal. 2007).Clubroot has been an important constraint to production of Brassica vegetablesworld-wide for more than a century, in part because of the economic losses that it causes,but more importantly because of the difficulties with the management of the pathogen.The earliest report of the disease dates back to the 13 th century, when clubroot symptomswere attributed to various causes including insects, malformations due to degeneration,and mineral deficiencies (cited in Karling 1968). Disease surveys from 1920 to 1950document the occurrence of clubroot in the Atlantic provinces of Canada (Conners et al.1956, Howard et al. 2010) and the pathogen has been present on Brassica vegetables inOntario, Quebec, and British Columbia for several decades (Conners et al. 1956, Reyes1974). Flooding in 1954 caused by Hurricane Hazel resulted in distribution of the1