Bacterium commonly used in plant genetic engineering is

The correct option is C $Agrobacterium$

Genetic engineering
The modification of the genetic material (RNA or DNA) of organisms to use them to produce commercially important substances is called genetic engineering.

The basic process of genetic engineering
The basic process of genetic engineering using plant cells is as follows:

• The gene of interest is removed from the cell of an organism and inserted into the vector DNA (Ti plasmid) to form recombinant DNA.
• The formation of the rDNA is done using enzymes, endonucleases, and ligases.
• The recombinant DNA is then transferred to the plant cell where multiple copies of the DNA are made or the gene is expressed.

$Agrobacteriumtumefaciens$
$Agrobacteriumtumefaciens$ is a bacterial plant pathogen that carries the Ti plasmid or tumour inducing plasmid (extrachromosomal DNA). The T-DNA segment of the Ti plasmid integrates itself into the plant cell’s genome to induce tumor formation in plants. This property of the plasmid makes it an effective vector for transferring foreign genes into plant cells.

$Corynebacterium$
$Corynebacterium$ glutamicum is used as a host in genetic engineering for the mass production of amino acids like L-glutamate, L-lysine, and carotenoids (lycopene). It cannot be used as a vector as it is a cell, because a gene that is inserted directly into a cell usually does not function.

$Bacillussubtilis$
$Bacillussubtilis$ is commonly used as a host, for the production of vitamins, inositol, acetoin, hyaluronan, etc., in genetic engineering. It cannot be used as a vector as it is a cell, because a gene that is inserted directly into a cell usually does not function.

$Salmonellatyphi$
$Salmonellatyphi$ is a Gram-negative bacterium that causes typhoid. Genetically engineered Salmonella typhi has the tumor-targeting ability. It cannot be used as a vector as it is a cell, because a gene that is inserted directly into a cell usually does not function.

Final answer
(A) $Agrobacterium$