The correct option is D Agrobacterium tumefaciens
Transgenic plants are ones that have new traits introduced into it using recombinant DNA technology. This is basically used to develop insect resistant, disease resistant plants and plants with improved nutritional value. Agrobacterium tumefaciens which causes the crown gall disease in plants is well known for its ability to transfer DNA between itself and plants, and is thus widely used an a genetic engineering tool in the production of transgenic plants.