Bacterial wilt caused by Ralstonia solanacearum is the main bacterial disease in potato. Solanum commersonii Dun. (cmm; 2n = 2x = 24, 1 EBN) is a native species to southern Brazil, Uruguay and Argentina with desirable traits for introgressive hybridisation breeding into cultivated potato such as resistance to R. solanacearum. In Uruguay, successful crosses between cmm and Solanum tuberosum Group Tuberosum (tbr; 2n = 4x = 48, 4 EBN) have been carried out with this objective, resulting in backcross 1, 2 and 3 progenies. The aim of this study was to characterise one backcross 3 progeny (BC3) using cytogenetic, genetic, morphological and agronomic descriptors. Resistance to R. solanacearum showed transgressive segregation and an association with plant architecture. Fifty-two percent of individuals had chromosome numbers close to cultivated potato with no evidence of preferential loss of cmm chromosomes. All BC3 individuals showed male sterility, probably due to nuclear-cytoplasmic interactions. Although there was wide segregation in morphological traits, most individuals resembled the recurrent tbr parents. A few more backcrosses combined with screening for bacterial wilt resistance may be necessary to allow for further recombination and removal of undesirable traits from cmm. The presence of BC3 individuals with chromosome numbers close to 2n = 48, combining morphological traits from tbr with good levels of resistance, suggests the occurrence of introgression events. This points to S. commersonii as one of the most promising genetic resources for potato breeding from the Southern Atlantic region.