Final answer:
Agrobacterium, especially Agrobacterium tumefaciens, is used to create transgenic plants by modifying and using its Ti plasmid to transfer desired DNA into plant genomes.
Step-by-step explanation:
The genus that has proved useful for manipulating plant cells is Agrobacterium, particularly Agrobacterium tumefaciens. This bacterium has been a key tool in the creation of transgenic plants due to its natural ability to transfer DNA to plant hosts. Researchers use a modified form of the Ti plasmid found in A. tumefaciens to remove tumor-causing genes and insert desired DNA fragments which then integrate into the plant's genome.