Country-Wide qPCR Based Assessment of Plasmodiophora brassicae Spread in Agricultural Soils and Recommendations for the Cultivation of Brassicaceae Crops in Poland.

Clubroot is a damaging disease of oilseed rape and vegetable brassicas worldwide, caused by the soil-borne protist Plasmodiophora brassicae Wor. Due to the long life of resting spores, the assessment of the pathogen abundance in agricultural fields can serve as a guideline for disease control at the country-wide level or the regional scale. Between 2013 and 2019, we collected 431 soil samples from fields cultivated with Brassicaceae crops throughout 16 provinces of Poland. The samples were subjected to qPCR based analysis of P. brassicae DNA concentration. From these data, the spore loads and gene copies g-1 soil were calculated and used to produce an assessment of the current clubroot risk potential at a country-wide and regional scale. The country-wide map, showing the spread of the pathogen in agricultural soils, was made using ArcGis software package implementing the interpolation with the Inverse Distance Weight method. The calculation of gene copies specific to P. brassicae helped to formulate the recommendations for farmers in respect to the cultivation guidelines. It showed a high risk of yield losses in defined regions of north, south-west and central Poland and an urgent need to undertake intensive preventative measures.