The cultivated potato, Solanum tuberosum, can be reproduced generatively through seeds and vegetatively through tubers. This may have evolutionary advantages: seeds may provide better survival under extreme conditions, such as frost or drought, and can remain viable in the soil for years. When conditions are mild, tubers survive in a dormant state for a couple of months. When conditions become favourable again, their fast and strong sprouting provides a clear competitive advantage over other plants in the same ecological niche. In traditional potato breeding, each breeding cycle starts with a cross between two genotypes, usually tetraploid varieties, followed by many years of selection and multiplication (see Chapters 2 and 3). The advantage of this approach is uniformity: the tubers are clones and thus genetically identical. The disadvantage is the low genetic gain in each lengthy breeding cycle, as the genetic composition of the two parental genotypes is just reshufﬂed, including alleles which negatively affect plant growth and development. As a result, potato yield has not signiﬁcantly been improved over the past century (Doucheset al., 1996; Vos et al., 2015). In addition, the reproduction of seed tubers is less than a factor 10 per season. It takes many years to build up sufﬁcient quantities of seed tubers for commercial production, and the risk of contamination by pathogens increases with each multiplication step. True potato seed (TPS) has been promoted as an alternative for seed tubers because TPS is easy to store and devoid of most soil-borne pathogens. In South Asia, East Africa and the Andes, TPS is used mainly by subsistent farmers (Almekinders et al., 1996). TPS is produced by crossing parent plants that have been selected to produce a hybrid variety. The parents are propagated vegetatively, similar to seed tuber propagation. As the parents of a TPS variety are heterozygous, all seeds of a TPS cultivar are genetically different. This results in a highly variable crop that is not acceptable in most markets, such as the high value markets of Europe and North America.
Pim Lindhout, Michiel de Vries, Menno ter Maat, Su Ying, Marcela Viquez-Zamora and Sjaak van Heusden, Solynta, the Netherlands
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