Fertility of somatic hybrids Solanum commersonii (2x, 1EBN) (plus) S-tuberosum haploid (2x, 2EBN) in intra- and inter-EBN crosses

Solanum commersonii (+) S. tuberosum hybrids with different endosperm balance numbers (EBN) and ploidy were used in various crossing schemes with 4EBN S. tuberosum cultivars and a 3EBN somatic hybrid to test their behavior in intra- and inter-EBN crosses and to derive a BC1 population for potato breeding. The somatic hybrids included 12 tetraploids (2n = 48, 3EBN), 18 hypotetraploids (2n = 43-47, 3EBN), 2 hexaploids (2n = 72, 4 or SEEN), and 5 hypohexaploids (2n = 63-70, 4 or SEEN). The results confirmed that in the potato, EBN is more important than actual ploidy in determining the success or failure of crosses. Indeed, crosses between some hypohexaploid hybrids and S. tuberosum cultivars gave the highest number of viable seeds per berry, and seed viability was similar to that of intra-EBN crosses between varieties. Inter-EBN crosses demonstrated that exceptions to the 2:1 maternal-paternal EBN ratio in the hybrid endosperm can sometimes be tolerated. However, an excess in maternal EBN dosage was better tolerated than an excess in paternal EBN.