Which one of the following is commonly used in the transfer of foreign DNA into crop plants?

The correct option is C

Agrobacterium tumefaciens

The correct option is C.

The explanation for the correct option:

1. The transfer of a particular gene or DNA in the host body is transformation.
2. Transformation is done in crops to raise genetically modified plants for creating disease-free, high crop yielding, vigor verities of crops.
3. Genetic modification can be achieved by transforming DNA from host to target species through the help of a vector.
4. Agrobacterium tumefaciens is a soil bacteria that cause crown gall disease in cotton. In the process of transforming DNA, it acts as a vector.
5. Desired genes are first transferred in Agrobacterium tumefaciens and when it infects the host plant, it transfers this gene into the host plant.
6. And hence genetic modification is achieved.

The explanation for the incorrect options:

Option A:

1. The genus Trichoderma includes fungal species which used as pesticides and fungicides.
2. It is not a vector species.

Option B:

1. Penicillium expansum is fungal species widely used in food and pharmaceutical industries due to its characteristic properties.
2. It is not a vector species.

Option D:

1. Meloidogyne incognita is a root-knot nematode that is a parasitic worm causing infection in the family Heteroderidae.
2. It is not a vector species.

Final answer: Agrobacterium tumefaciens is commonly used in the transfer of foreign DNA into crop plants.