R. A. Schilperoort

Summary: A mutant of A. tumefaciens strain B6S3, carrying the R factor RP4, was able to transfer its TI plasmid to various avirulent Agrobacterium strains and to a strain of Rhizobium. Strains carrying the TI(B6S3) plasmid were selected by their ability to utilize octopine. The isolates were able to induce tumours and exclude phage AP1. The tumours induced on Kalanchoë daigremontiana were rough and contained octopine. It was concluded that octopine utilization, phage exclusion, induction of rough tumours and synthesis of octopine in the tumours are determined by the TI(B6S3) plasmid. Tumorigenicity was determined this plasmid both in Agro-bacteria and in Rhizobium, suggesting that all the genes necessary for tumour induction are plasmid-borne.