2n gametes in the potato: essential ingredients for breeding and germplasm transfer

2n gametes are the result of meiotic mutations occurring during micro - and mega-sporogenesis. They have been identified in several plant species of different taxa. The potato is probably the crop plant where they have been most intensively studied and also more appropriately used for the genetic improvement of cultivated genotypes. This paper reviews how 2n gametes allow potato breeders to broaden the genetic basis of the cultivated Solanum tuberosum, introducing both new genes for the improvement of traits of interest and allelic diversity to maximize heterozygosity. We provide molecular and breeding evidence that, in the potato, 2n gametes represent a unique tool to transfer target genes from wild forms to the cultivated tetraploid gene pool. In fact, species directly crossable to S. tuberosum haploids can be exploited through sexual polyploidization crossing schemes. For those which have developed crossability barriers, specific crossing schemes based on ploidy bridges can be designed. In this paper we also give possible hypotheses to explain conflicting results on the genetic control and meiotic mutations responsible for 2n-gamete formation in the potato.