The Agrobacterium tumefaciens T-DNA gene 6(b) is an onc gene.

In this article it is shown that the T-DNA of Agrobacterium tumefaciens contains besides the well-known cyt and aux genes another gene with an oncogenic effect in plants. The gene in question is called 6(b) and causes the formation of small tumors in plant species such as Nicotiana glauca and Kalanchoe tubiflora.