THE LIFE‐CYCLE OF PLASMODIOPHORA BRASSICAE WORON. IN BRASSICA TISSUE CULTURES AND IN INTACT ROOTS

Abstract

Summary: The life cycle of Plasmodiophora brassicae was studied in stained preparations of Brassica napus and B. rapa callus tissue cultures and clubbed roots. Resting spores germinated in situ in callus cells to produce naked protoplasts which underwent plasmogamy to form multinucleate primary plasmodia. Mitosis then occurred and was followed by cleavage of the plasmodia into zoosporangia containing uninucleate zoospores. The zoospores were released and fused in pairs (without karyogamy) and then penetrated living callus cells where growth and mitosis took place to give multinucleate secondary vegetative plasmodia. The vegetative plasmodial nuclei fused in pairs and then underwent meiosis immediately. This was followed by cleavage of the plasmodial cytoplasm to yield uninucleate, haploid resting spores. P. brassicae had a haploid chromosome number of five in both 2‐year‐old callus cells and in recently harvested club‐root tissues.