Agrobacterium tumefaciens is a species of harmful bacteria that infects plants and is the cause of a lot of loss in various cultivated plants like walnuts, sugar beets, rhubarb, etc.
The bacteria has the ability to transfer a part of its DNA, also known as T-DNA into the plant's chromosomal DNA through its Ti plasmid.
Agrobacterium tumefaciens is very efficient in transfer of DNA as the T-DNA does not contain play a role in the functions required for movement and integration of the DNA. This has allowed scientists to use the bacterium as a means of modifying the DNA of plants which has been difficult to achieve using other methods using transposons and retroviruses.
For genetically modifying plants the genes that have to be added or modified are inserted into the bacteria and the recipient plant host is exposed to it. The genes are transferred to the plant by the bacteria with relative ease.
This has made Agrobacterium tumefaciens very useful in the field of genetically modifying plants to create characteristics that make them more useful.