Following an outline of the great variation in the primitive cultivars and wild species of potatoes in Latin America, the history of introductions and breeding procedures is discussed. Although two introductions occurred in the 16th century there were only few early introductions, and only very few varieties were grown in the early 18th century. The appearance of virus diseases, which debilitated established varieties but did not pass through true seed, led to widespread selection among seedlings and a vast increase in the number of varieties grown in the late 18th and early 19th centuries. The seedlings were from naturally-set berries and most would be selfed derivatives; selection among them may have reduced the gene-pool.
Improvements made by this selection were such that most 19th century introductions appeared primitive and, with only two known exceptions, they were discarded. Blight appeared in the mid 19th century and eliminated almost all varieties, including a number which were probably virus resistant, thus further reducing the gene-pool.
T. A. Knight commenced deliberate crossing before 1810 but this practice did not become widespread until the second half of the 19th century. Breeding among the few survivors of the blight epidemics and the few new introductions led, by the early 20th century, to a great many varieties being grown, e.g. over 500 in Britain and over 50 in North America, but they represented only a very limited gene-pool.
The pedigrees of modern potato varieties show that, although several 20th century introductions may occur in their ancestries, generally 80% or more of their genes are derived from varieties grown early this century. An appendix illustrates this for the recent varieties Pentland Dell and Croft. It follows that the gene-pool is still rather limited, and that modern varieties are somewhat inbred due to relationships between their parents and ancestors.