The correct answer is option 2: Agrobacterium tumefaciens. This bacterium is responsible for causing crown gall disease in plants. Crown gall is a disease that affects a wide range of plants, including fruit trees, grapevines, and ornamental plants. When Agrobacterium tumefaciens infects a plant, it transfers a piece of its own DNA, known as a plasmid, into the plant cells. This plasmid contains genes that cause abnormal growth and tumor formation in the plant. As a result, galls or tumor-like growths develop at the site of infection, typically on the stems or roots of the plant. These galls can impede the plant`s growth, reduce fruit yield, and even cause the death of the plant in severe cases.