1992 Volume 58 Issue 5 Pages 699-705
A highly germinative resting spore specimen of Plasmodiophora brassicae was obtained through a preparation procedure which involved rotting clubroot galls prior to purification process using Ficoll-400 discontinuous density gradient centrifugation. More than 60% resting spores thus prepared germinated at maximum. By using this specimen, the existence of a germination-stimulating factor (GSF) in some plants' root exudates was verified. The GSF was not lost by autoclaving, removed easily by dialysis, adsorbed partially to XAD-4 resin, and not extractable with diethyl ether and ethyl acetate. The GSF was therefore presumed to be a heat stable, fairly polar and low molecular weight compound. Since the GSF was found not specifically in root exudate of a clubroot-susceptible crucifer but also in that of a resistant crucifer and lettuce, the GSF was considered to be a factor not relating to clubroot resistance and host recognition.