Effectiveness of selection for quality traits during the early stage in the potato breeding population

Potato cultivars resistant to cold-temperature sweetening are of major importance to the processing industry producing both chips (crisps) and French fries. When most modern potato cultivars are maintained in cold storage to retard sprouting, the tubers accumulate reducing sugars, and the products become an unacceptable brown colour when fried. Selection for better processing quality during the early generations of a breeding programme could be of considerable advantage. Using a portable 'sugarmeter', which requires only a drop of sap from the tuber on a test strip, many samples can be efficiently surveyed for low sugar as early as the F 1 generation. Using seedlings of three test crosses, glucose and specific gravity of field-grown tubers, minitubers from greenhouses and microtubers from in vitro culture were compared after cold treatment. Although the mean glucose levels of minitubers and microtubers were higher than field-grown tubers, the correlation between the glucose contents of the three types of tubers was fairly high. A considerable genetic improvement was noted when progenies were grown as minitubers or microtubers, even though the response to selection for low glucose levels in minitubers and microtubers was lower than from direct selection from field-grown tubers. The specific gravity of field-grown tubers showed a significant association with freshly harvested minitubers and microtubers. Selection for low glucose content in minitubers can therefore save considerable resources in a breeding programme.