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Biological Soil Mapping - Infesttion By Plasmodiophora Brassicae And Soil Characteristics
1C. Aberger, 2A. Wallenhammar, 2A. Jonsson
1. Department of Soil and Environment, SLU, Skara , Sweden
2. Department of Soil and Environment, SLU, Skara, Sweden
Clubroot, caused by Plasmodiophora brassicae, is a soilborne pathogen that causes severe yield losses in many Brassica crops. It is a increasing problem in many Brassica growing countries. The spores survive for 15-20 years and might cause significant yield losses (>10%), already when 20% of plant are infected. An infestation with a couple of thousands spores/g soil is considered to have the potential to give such significant losses. Inoculum levels of >> 100.000 spores has been observed and this soil borne pathogens can be transported with soil. DNA-based methods have been developed to determinate levels of infestation in soil and a protocol to check farms is being developed. Presently has two steps. The first is to check the infestation on a field level. It is based on a sampling with approx. 40 subsamples along a W-line. This is followed by second point-sampling on fields where you suspect in-field variation in the infestation level. At a farm in the County Skaraborg, Sweden, fields were sampled using W-line and analysed. The levels of spores varied between field  from  <5 to >700 fg DNA equivalent to  >400.000 sporers/g soil. Two field where investigates using point sampling and analyzed for inoculum of  P.brasssicae, pH-value and amount -inof boron in the soil. The pH-value and boron are both reported to effect the development of clubroot and the combination of soil analysis of P.brassicae and boron opens a possibility to use variable rate application of nutrients ie boron to improve control of clubroot  in an integrated pest management approach. The pH-value and boron content varied between the fields and with-in the tested fields and this is presented together with possibilities of variable rate application of boron.
 
Keyword: Biological soil mapping, Clubroot, Plasmodiophora brassicae, in-field variation, boron