Which of the following methods is not commonly used for introducing foreign DNA into the plant cell? 

Bacteriophages are not commonly used for introducing foreign DNA into plant cells. Bacteriophages are viruses that infect bacteria and are mainly utilised for genetic engineering in bacterial systems.

(1) Agrobacterium-mediated transformation is a method commonly used for introducing foreign DNA into plant
cells. Agrobacterium tumefaciens is a natural vector that transfers DNA into plant cells.

(2) The gene gun or biolistic method is also commonly used for introducing foreign DNA directly into plant cells. It involves shooting microscopic gold or tungsten particles coated with foreign DNA into plant cells.

(3) ‘Disarmed pathogen’ vectors are derived from plant or animal based pathogens, like Agrobacterium or retroviruses respectively. Their pathogenic genes are removed and used to deliver foreign DNA into host cells during infection.