True Seed

• The fruits of a potato look like small green tomatoes and turn orange when ripe. Not all varieties produce fruit, which is poisonous because it contains a toxic substance called solanine. True seed cannot pass along any diseases from the parent plant like seed potatoes can. However, they require a longer growing season, the harvest is smaller and they will not "breed true," meaning they won't be identical to the parent plants.
  
  

Seed Potatoes

• Seed potatoes produce a harvest that is genetically identical to the parent plants. This assures a uniform crop, but any diseases that were in the parent plants are passed on via the seed potatoes. To combat this problem, grow certified disease-free seed potatoes, which authorities inspect throughout the growing season.
  
  

Sources

• True potato seed isn't as readily available in nurseries as seed potatoes. Online retailers such as Park Seed may be your best bet for finding potato seed.