Which pathogen delivers a piece of DNA known as 'T-DNA' to transform normal plant cells into a tumor?

Agrobacterium tumefaciens

The correct answer is Option (2) –Agrobacterium tumefaciens

Agrobacterium tumefaciens is a pathogenic bacterium that naturally infects several dicot plants. It carries a piece of DNA known as "T-DNA" (transfer DNA) on its tumor-inducing (Ti) plasmid. When this bacterium infects normal plant cells, it transfers the T-DNA into the plant cell's genome. The T-DNA then integrates into the plant's DNA and causes the transformation of normal plant cells into a tumor. The transformed tumor cells produce chemicals required by the pathogen, promoting its growth and providing nutrients to the bacteria. The process of delivering T-DNA into plant cells is an essential step in plant genetic engineering, allowing the introduction of desirable genes into plants for various purposes, such as crop improvement and biotechnology applications.