INTRODUCTION

Wild species are products of natural evolution in centres of diversity. They are not manipulated on purpose or used by man. Their evolution is brought about by the interaction of abiotic and biotic factors with the genetically variable plant populations. This has resulted in the wealth of variation found among and within species. In the centres of diversity the species may coexist but remain largely separated by external and internal barriers developed in the course of evolution.

Domesticated or cultivated plants have derived from the wild species and are manipulated by man both agronomically and genetically in order to improve their adaptation to human needs. The potato has its main centre of diversity in the mountainous regions of Latin American countries. Here the potato was domesticated and has been grown for several millennia. These primitively cultivated potatoes comprise eight Solanum species: the diploids S. phureja, S. stenotomum, S. goniocalyx and S. ajanhuiri, the triploids S. chaucha and S. juzepczukii, the important tetraploid S. tuberosum ssp. andigena and the pentaploid S. curtilobum.

Not until the latter half of the 16th century was the potato introduced into countries outside Latin America, first into Europe, from there into North America and later on all over the world. The immediate ancestor of our present-day autotetraploid S. tuberosum ssp. tuberosum cultivars is the autotetraploid S. tuberosum ssp. andigena. Although initially only few genotypes of S. tuberosum ssp. andigena were introduced, a large number of different S. tuberosum ssp. tuberosum cultivars adapted to various conditions has been derived from that material.