Introgression of resistance to late blight (Phytophthora infestans) from Solanum pinnatisectum into S-tuberosum using embryo rescue and double pollination

Efforts to generate hybrids from crosses of Mexican diploid 2x(1EBN) species x 2x(2EBN) Solanum tuberosum haploids via embryo rescue and double pollination were conducted. The species included were S. bulbocastanum, S. pinnatisectum and S. trifidum. The species S. phureja was used as a second pollinator. After 3, 077 pollinations were made during the spring and summer of 1995, 31 potential hybrids were obtained; however, they were discarded because of their S. phureja second pollinator characteristics. The length of time before conducting embryo rescue [20-25 days after pollination (DAP)] was presumed responsible for this failure. In 1996, 3,288 pollinations were made, resulting in 184 fruit. Embryo rescue was performed between 15 and 20 DAP and resulted in 3, 867 embryos of which 530 developed into seedlings. In January of 1997, a single unique hybrid was discovered in this population and was almost discarded because of its S. phureja anthocyanin nodal banding marker. This diploid hybrid arose from a cross between the haploid US-W 13,089 (Sebago) x S. pinnatisectum (PI 275233). The hybrid was hypoploid (22 chromosomes). Its hybridity was confirmed through morphology, chromosome number and RAPD analysis. Its resistance to late blight was tested in an unsprayed replicated experiment at the UW Agricultural Research Station at Hancock, WI during the summer of 1997, where the results indicated a high level of field resistance. The hybrid exhibited a low degree of male and female fertility. From meiotic analysis, it was evident that normal pairing between the two genomes occurred, although the presence of univalents was observed. No hybrids with S. bulbocastanum and S. trifidum were obtained. These results support the view that transfer of valuable characters from S. pinnatisectum to S. tuberosum is feasible; however, aneuploidy and the presence of univalents may inhibit this effort.