107 Interspecific Hybridization in Potato by Unilateral Sexual Polyploidization L. Augustin, S. Salazar, M.I. Baggio, D.A. Bisognin M.F. Grando, M. Valiati and M. Suzin Universidade Federal de Santa Maria Universidade de Passo Fundo (UPF) Centro de Ciências Agrárias Faculdade de Agronomia e Medicina Veterinária Santa Maria Laboratório de Biotecnologia Vegetal Rio Grande do Sul Passo Fundo, RS Brazil Brazil Keywords: Solanum tuberosum, wild species, unreduced gametes, introgression, genetic breeding Abstract This work was carried out in the Laboratory of Plant Biotechnology at University of Passo Fundo, in South Brazil. The objective of these experiments was to test, for local condition, the hybridization technique strategy by sexual unilateral poly- ploidization in potato in order to transfer genes from wild diploid into the tetraploid cultivated species. Initially, the temperature effect on the occurrence of unreduced (2n) pollen grains in two diploid clones at temperature of 10, 15, 20, 25, 30 and 35°C was evaluated. The highest frequency of unreduced pollen grains was observed in temperatures of 15°C with an average of 30.7% for one clone and 7.6% for the other. Both clones were used as male parents in crosses with tetraploid cultivars. A total of 109 crosses were performed, and in 14 of them, 2,4-D was applied after pollinations. After pollination, three fruits were obtained from 14 flowers that were treated with 2,4D. However, only one of them was fertile, producing five plants, which presented morphological traits from both parents, eliminating the self-pollination hypothesis. The number of mitotic chromosomes of F 1 plants was 48. This tetraploid ploidy level shows that the tetraploid cultivar oosfere was fertilized by the unreduced pollen of diploid species. This indicated the overcoming of a critical restriction for the genes transference between plants with different ploidy levels had occurred. Although this strategy needs to be optimized, this work shows the possibility of using non reduced pollen grain as a bridge to transfer desirable traits from wild gene pool to the cultivated one under our conditions. This enlarges the genetic variability of the crop, increasing the potential of developing new potato cultivars having disease resistance, good eating quality and superior agronomic traits. INTRODUCTION Potato (Solanum tuberosum L.) is an important crop plant and one of the most important food supplies in the world. Among seven species of cultivated potato, the tetraploid (2n=48) S. tuberosum subspecies tuberosum which originated in South America, is the most important species (Hawkes, 1990). Potato probably has the widest genetic diversity among related wild species than any other cultivated plant (Hawkes and Jackson, 1992) with more than 70% of the wild species being diploid (2n=24) (Hawkes, 1994). For breeding programs of the tetraploid potato (Solanum tuberosum), both wild and cultivated diploid relatives are valuable sources of genetic diversity (Janski and Peloquin, 2006). The South American diploid species S. microdontum has shown high levels of resistance to late blight (Douches et al., 2001). Strong hypersensitive reaction or infection efficiency, lesion growth rate and sporulation time were associated with high levels of resistance in S. microdontum (Colon et al., 1995). One selected clone (PI595511-5) was crossed with a diploid breeding clone MSA133-57 [(S. tuberosum × S. chacoense) × S. phureja]. From this cross, the clones SMIDLB1-140 and SMIDLB1-150 were selected for late blight resistance, early maturity, tuber processing quality and production of Proc. XXVIII th IHC – IS on New Developments in Plant Genetics and Breeding Ed.: J.M. Leitão Acta Hort. 935, ISHS 2012