166 Adv. Hort. Sci., 2009 23(3): 166-170 Received for publication 6 May 2009. Accepted for publication 23 July 2009. Field performance and resistance to tuber soft rot of potato clones derived from sexual polyploidization A. Di Matteo, G. Caruso, A. Barone, R. Aversano, L. Frusciante, D. Carputo Dipartimento di Scienze del Suolo, della Pianta e dell’Ambiente e Produzioni Animali, Università di Napoli Federico II, Via Università 100, 80055 Portici (NA), Italy. Key words: Erwinia carotovora, phenotypic selection, Solanum tuberosum, Solanum phureja, tuber yield. Abstract: Unilateral sexual polyploidization through 4x x 2x crosses is widely used to introgress genes from the diploid gene pool to the tetraploid cultivated potato Solanum tuberosum. Clones of eight 4x x 2x families, from crosses between four tetraploid cultivated potatoes and two diploid S. phureja – S. tuberosum hybrids, produc- ing 2n pollen, were evaluated for yield performances and resistance to tuber soft rot. Significant differences in terms of tuber yield and number were found between families and clones, with several clones outyielding their tetraploid parents. The source of variation due to females (4x females GCA) was significant for both tuber yield and number. A number of clones displayed inheritance of resistance to tuber soft rot. No relationship was found between agronomic traits and resistance to soft rot. Results suggest that the genotypes produced represent genet- ic material with good potentiality in the constitution of new genotypes with interesting trait combinations. 1. Introduction Potato breeding has generally been directed at two ploidy levels: the tetraploid and the diploid. The former is essentially based on phenotypic recurrent selection, involving crosses between tetraploid varieties and/or advanced clones, and then field evaluation and selec- tion (MacKay, 2006). Due to the high levels of het- erozygosity of cultivated S. tuberosum, segregation of traits is expected in the F 1 generation. After several years of clonal selection, superior clones are tested in different locations to estimate the extent of genotype x environment interaction. To exploit the wealth in allel- ic diversity of tuber and non-tuber bearing related species, to increase the frequency of multiallelic loci, and also to deal with simpler inheritance patterns, sev- eral breeding programs have been directed at the diploid level (Bradshaw et al., 2006). They require the use of diploid (2n=2x=24) germplasm as a source of useful traits, and S. tuberosum haploids (2n=2x=24) to “capture” the genetic diversity (Carputo et al., 2000). Following 2x x 2x crosses, diploid hybrids are pro- duced and selected for traits of interest, exploiting the advantages of disomic rather than tetrasomic inheri- tance of characters. Diploid hybrids are also selected for 2n gamete production, to be employed in unilateral sexual polyploidization schemes with tetraploid potato (4x - 2x crosses) to re-establish the tetraploid level of the cultivated S. tuberosum. The use of 2n gametes not only allows the restoration of the tetraploid level, but also permits the transmission of large amounts of the parental heterozygosity and epistatic interactions with- out disruption by recombination (Peloquin et al., 1999). Tetraploid progenies obtained are then included in field evaluation and clonal selection programs. This breeding strategy has already been used to introgress into the cultivated gene pool allelic diversity and use- ful genes from various species, including S. berthaultii, S. tarijense, S. bukasovii, S. sparsipilum, S. phureja, S. multidissectum, S. chacoense (Jansky, 2006). Among diploid tuber-bearing Solanum species, S. phureja is very interesting. It has a number of note- worthy traits that can be incorporated into the cultivat- ed potato, such as resistance to biotic stresses, improved flavor, reduced cooking time, and high ascor- bic acid, carotenoid and dry matter content in the tubers. Recently, it has also become a source of genom- ic resources (Evers et al., 2006). However, has some undesired traits, such as tuber eye depth and lack of tuber dormancy that may hamper its use in breeding. In several breeding programs S. phureja has received much attention. One of the most successful uses of S. phureja has been by the potato breeding program at Scottish Crop Research Institute (SCRI) in Dundee, where a collection of adapted clones has been devel- oped (Bradshaw and Ramsay, 2005).