71 Plant Protect. Sci. Vol. 52, 2016, No. 2: 71–86 doi: 10.17221/87/2015-PPS Clubroot Caused by Plasmodiophora brassicae Wor.: a Review of Emerging Serious Disease of Oilseed Rape in the Czech Republic Veronika ŘIčAŘOVá, Jan KAZDA, Khushwant SINGH and P avel RYšáNEK Department of Plant Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Prague, Czech Republic Abstract Řičařová V., Kazda J., Singh K., Ryšánek P. (2016): Clubroot caused by Plasmodiophora brassicae Wor.: a review of emerging serious disease of oilseed rape in the Czech Republic. Plant Protect. Sci., 52: 71–86. Winter oilseed rape is the second most frequently grown crop in the Czech Republic. Clubroot, caused by Plasmo- diophora brassicae (Wor.), was previously a problem in production of vegetable. The disease has been spreading on winter rape ( Brassica napus L.) over the past four years. Infected stands were reported throughout the country in autumn 2011. The pathogen is probably widely spread in the whole country, its incidence depends on suitable weather conditions. Every field with clubroot is considered as contaminated for many years. The amounts of inoculum and its distribution are not sufficient yet, but this is just the initial stage of colonisation. There is a similar situation resem- bling experiences from other countries (Canada, Germany) where clubroot has gradually expanded in the last 15 years. Keywords: winter oilseed rape; Brassica napus L.; clubroot disease; biology; pathopypes; resistance Introduction Winter oilseed rape (Brassica napus cv. napus, the family Brassicaceae) is one of the most widely grown crops in the world (USDA, GOV; http://www.fas. usda.gov/oilseeds/Current) and also in the Czech Republic, where its production ranks second only after cereal crops. In 2013 the oilseed rape was grown on a record production area (418 808 ha) followed by a slight decrease (389 297 ha) in 2014. However, the 2014 yield was high – 3.95 t/ha – the highest in the history of oilseed rape production in the Czech Republic and former Czechoslovakia (CSO – Czech Statistical Office; https://www.czso.cz/csu/czso/ zem_ts). Together with the increasing concentration of oilseed rape in the country more problems with pests and pathogens occur. One of them, the soil- borne plant pathogen Plasmodiophora brassicae Wor., causes the clubroot disease of crucifer crops including oilseed rape (Hwang et al . 2012). P. bras- sicae occurs in more than 60 countries including the Czech Republic and it causes 10–15% loss in the production of oilseed rape worldwide (Dixon 2009a). The potential hosts of P. brassicae could be all species from the family Brassicaceae, including weeds (Dixon 2009a). Until the season 2011 symp- toms appeared regularly on oilseed rape in northern Moravia and southern Bohemia, where the clubroot was first reported by Rod (1996) three decades ago. In those areas with the long tradition of cruciferous vegetable production, because in the past the clubroot was a problem of vegetable production in the Czech Republic (Rod 1996). Over the past four years, the disease has been spreading on oilseed rape. The first strongly infected stands were reported throughout the country in autumn 2011 (Figure 1 – red marks). The serious infestation was found on 44 farms, mainly in Bohemia, northern Moravia and in the Czech- Moravian Highlands (Kazda et al. 2013). It is known Supported by Ministry of Agriculture of the Czech Republic, Project No. QJ1310227, and by the Czech University of Life Sciences in Prague, Project No. 20142031.