Winter oilseed rape (Brassica napus) is an important crop in the Czech Republic and Poland. Clubroot disease caused by the pathogen Plasmodiophora brassicae is a serious and still-growing problem for oilseed rape growers in both countries. The aim of this study was to evaluate the pathotype composition of P. brassicae populations from the Czech Republic and Poland, according to the three evaluation systems, and to determine soil inoculum loads for representative fields via traditional end-point PCR as well as quantitative PCR analysis. There were considerable differences between the populations of P. brassicae from both countries, and the number of pathotypes varied depending on the evaluation system and the threshold used to distinguish susceptible vs. resistant plant reactions. This is the first study comparing the effect of different thresholds. Using an index of disease (ID) of 25 % to distinguish susceptible vs. resistant reactions, there was a total of seven pathotypes identified based on the differentials of Williams, five with the system of Somé et al., and 18 with the European Clubroot Differential (ECD) set. However, based on a threshold of 50 %, there were nine pathotypes according to the evaluation system by Williams, four based on the differentials of Somé et al., and 15 with the ECD set. Changing of the thresholds led to the reclassification of some pathotypes. Several pathotypes were common in both countries. High amounts of pathogen DNA were found in many of the field soils analysed by quantitative PCR. There was a weak correlation between soil pH and infestation of P. brassicae for the Polish soils.
AbstractŘičařová 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 Plasmodiophora 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 resembling experiences from other countries (Canada, Germany) where clubroot has gradually expanded in the last 15 years.
Clubroot is caused by the pathogen Plasmodiophora brassicae Woronin and has become a serious problem in oilseed rape production in the Czech Republic. The disease was previously widespread in commercial vegetable production and in hobby gardens. Whereas previously restricted only to the NE, since 2010 oilseed rape clubroot has been spreading across the whole country. A five-year monitoring of clubroot occurrence based on disease symptoms detection on oilseed rape fields was accomplished by the Union of Oilseed Growers and Processors. The presence of P. brassicae and clubroot symptoms was reported in all regions of the Czech Republic, except the Ústecký region, and in 31 out of 76 districts. At present, at least 130 fields are known to be infested by the pathogen, but this number is very likely underestimated. Some soil samples were also tested using the conventional polymerase chain reaction (PCR) method to evaluate the soil usability. All 14 suspected samples tested positive.
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