HYBRIDIZATION BETWEEN GP TUBEROSUM HAPLOIDS AND 1EBN WILD POTATO SPECIES

Diploid wild potato species, classified as 1EBN (Endosperm Balance Number), do not cross with tetraploid or diploid forms of S. tuberosum Gp. Tuberosum. The crossing of 2n pollen producing 1EBN clones as well as chromosome-doubled 1EBN clones with Gp. Tuberosum haploids was initiated to overcome this hybridization barrier. The screening of eleven 1EBN species, S. brachistotrichum, S. bulbocastanum, S. cardiophyllum, S. chancayense, S. commersonii, S. etuberosum, S. fernandezianum, S. jamesii, S. mochicense, S. pinnatisectum and S. trifidum, resulted in the identification of 2n pollen producers in eight of the species examined. Direct hybridization with Gp. Tuberosum haploids utilizing the above-mentioned crossing scheme was successful with S. chancayense and S. commersonii. The hybrids obtained, however, were male and female sterile. Abnormal microsporogenesis in the hybrids was postulated to be the result of an interaction between Gp. Tuberosum cytoplasm and nuclear genes contributed by the 1EBN male parent. Analyses of the growth of 1EBN species' pollen tubes in the stigma/style of Gp. Tuberosum haploids were also conducted. Interspecific incompatibilities were observed with the most severe forms found with the use of species in the Series Etuberosa. The use of the Endosperm Balance Number theory can aid in designing crosses which overcome barriers to successful endosperm development. Sterilities in the hybrids obtained as well as interspecific incompatibilities will also need to be addressed, however, before 1EBN species germplasm can be successfully utilized for the improvement of the cultivated potato.