INTRODUCTION

The utilization of true potato seed (TPS) for potato production has developed rapidly in many parts of the world since 1978, when TPS was adopted as a principal research programme at the International Potato Center (CIP) in Peru. By 1984, the range of TPS activities had become extensive (International Potato Center 1984). In 34 countries, research on TPS was being conducted at the experiment station level, while 10 countries were involved in on-farm research. TPS was being used at that time by farmers in Sri Lanka, the People's Republic of China, Rwanda, Samoa and in the Philippines.

Much of the early work on TPS agronomy was carried out using open pollinated seed collected from cultivars which produced large quantities of true seed. One of the problems with this true seed was the heterogeneity of some of the progenies, because of the high heterozygosity of the mother plants, which could not be compared with clones in terms of uniformity. Initially it was felt that complete uniformity might not be necessary for potatoes from TPS. Researchers at CIP had been encouraged in this belief by the fact that they had observed farmers in Costa Rica (Central America) mixing white-skinned and red-skinned varieties at harvest. It was thought that this might also be typical of the situation in other countries. Subsequent studies have indicated however that uniformity is important, not only with regard to phenotype in the field, but also with regard to maturity, pest and disease resistance and cooking quality.