Potatoes are a vegetatively propagated crop, and many disease organisms including several viruses and a viroid are disseminated in tubers. The important role that tubers play in virus spread is recognized by the strict requirements for foundation or certified seed production. For example, all four classes of New York foundation seed shall not show a total in excess of ½ percent of mosaic, leafroll, or spindle tuber viroid based upon a winter test performed in Florida. Seven viruses and spindle tuber viroid are recognized as important in the state from either a production or a seed certification standpoint. The viruses include potato leaf roll virus, potato viruses Y, X, A, S, M, and alfalfa mosaic virus, with the first three being the most important.