INTRODUCTION

In common with applications of tissue culture to other crops, there is a fundamental divide between culture systems of potato in which the organization of meristems is maintained, and those where cultured cells pass through a disorganized callus phase. In tissue explants where meristem organization is maintained, and from which whole plants can be regenerated, such regenerated plants are normally uniform and true-to-type. Thus techniques such as micropropagation, virus elimination through meristem culture, embryo rescue, ploidy manipulation and germplasm storage, which employ this approach, are widely used by breeders as practical adjuncts to plant breeding programmes. However, when potato cells pass through a callus phase, the plants subsequently regenerated may well exhibit differences from the original genotype. Variation so produced has been termed somaclonal variation, and its nature needs to be outlined and taken account of in any manipulations that involve production of callus tissue.

In this article, manipulations of potato that involve callus culture are described, in particular techniques of protoplast fusion and somaclonal variation. The aim of work described here is to induce and exploit useful genetic changes in potato, and to evaluate the practical potential of these techniques in plant breeding.

PROTOPLAST CELL CULTURE AND CONSEQUENCES OF A CALLUS PHASE

Regeneration from explants

It is now well established that whole plants of potato can be regenerated from excised tissue segments such as leaf, stem or tuber.