Development of resting spores on plants inoculated with a dikaryotic resting spore of <e1>Plasmodiophora brassicae</e1> (K. Narisawa and T. Hashiba)

A dikaryotic resting spore or two monokaryotic resting spores of <e1>Plasmodiophora brassicae</e1> were inoculated onto 1-d-old seedlings of <e1>Brassica campestris</e1>. The relative DNA content of a nucleus in a dikaryotic resting spore corresponded with that of a haploid nucleus in a monokaryotic resting spore. Plasmodia and zoosporangia were observed within the galls in some root cortical cells approximately 2 mo after inoculation. Resting spores were also formed within the galls in some cortical cells, and root hair infection was observed. The frequency of resting spore formation in <e1>B. campestris</e1> seedlings inoculated with a dikaryotic resting spore or two monokaryotic resting spores was 26·2 and 3·6%, respectively. The results indicate that the life-cycle of <e1>P. brassicae</e1> was completed on plants infected with a dikaryotic resting spore or by two monokaryotic resting spores.