The effect of chromosome doubling on fertility,meiotic behaviour and crossability of Solanum etuberosum × S. pinnatisectum

Summary Doubling the chromosome number of sterile F₁ hybrids of S. etuberosum × S. pinnatisectum resulted in fertile allotetraploid hybrids (code 4x-EP) with nearly normal chromosome pairing at meiosis. Many seeds were obtained from selfing and sibbing, but seed set varied considerably. The 4x-EP hybrids were successfully crosses as females with S. stoloniferum and S. polytrichon and as males with S. verrucosum. The crosses with S. stoloniferum and S. polytrichon were carried out reciprocally and unilateral incompatibility was detected. Crosses of 4x-EP hybrids as males onto S. phureja and S. tuberosum cv. Gineke produced parthenocarpic berries only. Nearly 1700 flowers of colchicine-doubled S. pinnatisectum × S. bulbocastanum and the trispecific hybrid (S. acaule × S. bulbocastanum) × S. phureja did not yield a single berry after pollination with a pollen mixture from 20 4x-EP plants.It is concluded that the use of the bridging species S. pinnatisectum and either S. stoloniferum, S. polytrichon or S. verrucosum may enable gene transfer from the non-tuberous Etuberosa species to potato cultivars.