Paul Bethke, USDA-ARS Vegetable Crops Research and Department of Horticulture, University of Wisconsin-Madison 

There is worldwide interest in converting potato from a tetraploid, vegetatively propagated crop to a diploid inbred-hybrid crop that is propagated from true seed. Whether or not this can be done successfully depends on a wide range of research activities, some of which are scarcely underway. It is clear that potato genetics research will benefit from using diploid lines. Genomic sequencing and computational analysis tools will allow researchers to study the genetics of diploid potato in unprecedented ways. Parent selection and progeny identification based on genetic markers will produce improved breeding stocks. Research using targeted molecular manipulations, such as gene editing, will be more informative and will lead to more rapid genetic improvement when done with diploid rather than tetraploid germplasm. Diploid potato varieties can be expected have a few clear advantages over tetraploid varieties. Varieties can be maintained as true potato seed (TPS) rather than as tissue culture plantlets. Variety expansion will be more rapid than with the current system. There are clear disadvantages of diploid varieties, however, and significant areas where the path forward is unknown. Seed certification efforts will have to expand to guard against TPS-borne diseases. A method for producing TPS on a large scale without hand pollination is not available. Intellectual property laws for TPS-propagated potato varieties do not exist. Regulations for moving TPS between countries will need to be modernized. Less obvious concerns exist at all levels. To an unknown extent, potato variety development in the United States will shift from public to private breeding. As lines become more inbred, breeders will be more reluctant to share advanced germplasm than they are today. Seed costs will likely increase. The greatest unknown is whether diploid varieties will be commercially successful. New diploid varieties must produce economic benefits that cover the cost of variety development. For the grower, this means that economic returns from increases in productivity or crop quality must cover increases in seed cost. To achieve this goal, diploid varieties will need to meet the high standards expected by the industry and have substantial increases in marketable yield or decreases in input costs when compared with the best tetraploid varieties.