Use of bridge species and rescue pollination for introducing the wild diploid 1EBN species germplasm to cultivated potatoes

The commercial potato is an autotetraploid with a narrow genetic base, while wild diploid potato species are sources of genetic diversity and genes for resistance to most of the biotic and abiotic stresses along with quality traits. However, the utilization of wild species in potato breeding is restricted by pre- and post-zygotic crossing barriers resulting from different ploidy levels, endosperm balance number, or genomic structure. Diploid 1EBN species, due to such barriers, are considered the tertiary germplasm for potato breeding. Here we used Solanum verrucosum, a rare self-compatible wild diploid potato, as a bridge species along with rescue pollination and indolebutyric acid (IBA) application for germplasm transferring from four 1EBN species including S. commersonii, S. bulbocastanum, S. cardiophylum, and S. pinnatisectum. Results showed that rescue pollination for fruit retention seems slightly better than the IBA application. The same results were also obtained for the seed set. IBA mainly led to fully parthenocarpic fruits. Seeds obtained from these crosses had gibberellic acid resistance dormancy and low germination capacity. As it was expected, the crossability of S. commersonii with S. verrucosum was better than the other three species. Interspecific S. verrucosum × S. commersonii hybrids showed both male and female fertility. However, they were crossable with the cultivated diploid potato species S. phureja just as the female parent.