1978 Volume 44 Issue 4 Pages 432-439
The root hair infection with Plasmodiophora brassicae Wor. was the most frequent in the 2-3cm part of the tap root below the hypocotyle of Chinese cabbage (cv. Kinshyo-hakusai) grown in the soil infested with 106 spores/g dry soil at 25C for 12 days. Clearly differentiated zoosporangia were found at first in the infected root hair cells in 7-day-old seedlings, followed by the completely evacuated zoosporangial clusters in 8-day-old ones. No root hair infection was found at the lowest spore density of 10 spores/g dry soil, neverthless severely clubbed roots were formed. Although the frequencies of infected root hairs, clubbed plants, and the disease index were increased with the spore density, the spore density correlated only with the disease index (r=0.82**). The minimum spore density required to produce clubbed roots was more than 3.55 spores/g dry soil. There was no correlation between the root hair infection and the disease index. In Chinese cabbage seedlings used in this study, it seems that a few infected root hairs may be associated with subsequent club formation.