Improved potato varieties are obtained by bringing together desirable combinations of genes. Generally this is achieved by sexual hybridization followed by selection of plants with the desired characters. New techniques are now in existence that enable specific genes to be inserted into all the cells of a particular plant, leaving the residing somatic genome largely intact. In principle, such foreign genes can originate from any organism. They may be naturally existing genes, genetically engineered derivatives or may even consist of newly designed and chemically and/or biochemically synthesized DNA.

In this chapter three aspects of introducing specific genes into potato are discussed. Firstly the transformation of potato cells by direct infection of wounded shoot cultures of cultivars with Agrobacterium, the acquired growth properties of such transformed cells and the isolation of transformed plants. Secondly, the initial analysis of the expression of genes introduced into potato and finally implications for future genetic manipulations in potato, based on the known effects of genes already introduced.

Possible alternative ways of obtaining potato plants transformed with specific foreign DNA are omitted or only mentioned in passing. This is not to express a preference for direct Agrobacterium infections but simply because experimental progress in potato using other systems is less advanced.