Tomatoes, Potatoes and Rhubarb are Toxic to Pets
Tomatoes, potatoes and rhubarb contain oxalates, which trigger abnormalities with the nervous system, kidneys and digestive tract. Especially toxic are green tomatoes, green potatoes, potato skins, and tomato leaves and plants, can trigger tremors, seizure and heart arrhythimia, so tomatoes should never be given to dogs.
The tomato plant is toxic to dogs (and humans too). The fruit is not toxic. I occasionally add tomatoes to the veggie mix I feed my dog, with no problems.