Effect of the amelioration of soil acidity and continuous cropping of cruciferous vegetables on the incidence of clubroot disease and resting spore density in soil

pp. 891–896
In order to elucidate the effect of converter furnace slag applied as a liming amendment and continuous cropping of Qing gin cai ( Brassicae chinensis L.) or leaf daikon ( Raphanus sativus ) on the incidence of clubroot disease and the resting spore density in soil, pot cultivation tests were carried out. In the pot tests, pH(H₂O) was 5.2–6.1 in the non-application pot, and 7.1–7.6 in the pots receiving an application of converter furnace slag.
A significant incidence of club-root disease was apparent in the non-application pots of Qing gin cai . The resting spore density in the soils decreased soon after harvesting, but then increased after mixing the infected roots and soils.
On the other hand, the incidence of the disease was suppressed significantly, in application pots of continuously cropped Qing gin cai . Furthermore, the resting spore density in these soils decreased with repeated cultivation.
These results agreed well with the results from field cultivation tests that the authors have already reported. Macfarlane has reported that the suppression mechanism of clubroot disease brought about by the amelioration of soil acidity is effected through the inhibition of resting spore germination.
In this study, the decrease of resting spores density was associated with the cultivation of Qing gin cai under conditions of high soil pH. From these results, it is concluded that the suppression mechanism is caused by some phenomenon that occurs after the primary zoospore is infected with the root hair.
Until now, avoidance of continuous cropping of susceptible cruciferous vegetables was promoted as one of the most fundamental countermeasures for the control of clubroot disease. However, continuous cropping of suceptible cruciferous vegetables will be a useful technique to decrease resting density specifically under conditions of high soil pH.