Chromosome pairing in auto-allotetraploid (AAAB) interspecific hybrid potatoes

The commercial potato Solanum tuberosum L. 2n = 4x = 48 is a tetrasomic (AAAA) species, with a narrow genetic base. Wild genomic allotetraploid species such as S. stoloniferum (AABB) have great importance in potato breeding, but getting homoploid hybrid by direct crossing between the cultivated potato and wild allotetraploid species is difficult due to genic imbalance in endosperm. In this study chromosome pairing during metaphase I of meiosis in three exceptional homoploid hybrids between S. stoloniferum × S. tuberosum was analysed. The main chromosome configuration at metaphase I was bivalent and univalent with the frequencies of 15.17 and 6.56, respectively. Low frequency of trivalent (1.88) and tetravalent (0.7) was also observed. Further unequal segregation in first and second meiotic division was observed. Results indicated that although one genome of stoloniferum was different from its other genome as well as those of tuberosum, intergenomic pairing occurred between A and B genomes.