Tumor induction by Agrobacterium rhizogenes involves the transfer of plasmid DNA to the plant genome.

The DNA from tumors of Nicotiana glauca initiated by strains of Agrobacterium rhizogenes was shown to contain sequences that are homologous to the root-inducing (Ri) plasmid of the bacterium. Two independently established tumor lines contained a similar portion of the Ri-plasmid. The Ri-plasmid also hybridized to DNA fragments from uninfected N. glauca. A cosmid clone of the Ri-plasmid encompassing the region containing the Ri-plasmid sequences that are stably transferred to the plant also hybridized to the Ri-plasmid-related fragments found in uninfected plants. Five of six tumor lines tested produced a tumor-specific compound that is similar to agropine.