SUMMARY: Explants of young tumour tissue from several Brassica species infected with plasmodia gave rapid callus growth on medium containing 2,4-dichlorophenoxyacetic acid and coconut milk. Degeneration of the callus followed as resting spores were formed. The resting spores germinated and primary plasmodia and zoosporangia developed in some cells, then secondary plasmodia reappeared and normal callus growth was resumed; thereafter all stages of the parasite life-cycle were present in active cells. This situation has been maintaned for over 18 months by 8-weekly transfer of calluses to new medium. Callus clones containing only vegetative plasmodia were established on a coconut-milk + 2, 4-dichloro-phenoxyacetic acid medium. Sporogenesis did not occur readily in these clones unless callus was transferred to a kinetin + α-naphthylacetic acid medium or to other media which did not contain 2,4-dichlorophenoxyacetic acid. Stages of the life-cycle found in callus appeared similar to those in intact hosts, while zoosporangia were formed in the root hairs of organ cultures infected with callus-produced resting spores. It was concluded that on suitable media may be maintained in complete balance with host callus.


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