Abstract
Vertical distribution of the clubroot pathogen, Plasmodiophora brassciae, in 7 heavily infested fields in Gifu Prefecture, was determined by the use of a susceptible plant, Chinese cabbage (Brassica campestris ssp pekinesis), as an indicator plant. Soil was sampled at every 5 cm depth from the soil surface to the subsoil. The pathogen sufficient to cause the disease was detected in soil above 5 cm deep, but not in soil below 40 cm deep in every field tested irrespective of their soil types and cropping histories. The disease severity was greatest in soil 0-15 cm deep, but varied among the fields. It decreased gradually with the depth of soil. In sandy loam, alluvial soil, with a deeper low layer, the pathogen was detected even at depths of 30-40 cm. In the field with shallow plowed layer above 30 cm deep, the disease occurred even in the subsoil layer where the pathogen might be distributed by direct tillage. The disease incidence and the vertical distribution of the pathogen in heavily infested fields seem not to be affected by once cropping with sweet corn (Zea mays var. saccharata),taro ( Colocasia esculenta) and eggplant ( Solanum melongena) or even by soil pH, differed slightly at depths of soil.
