A breeding scheme is outlined which broadens the genetic base of the potato by incorporation of germplasm fromS. chacoense (Argentina) with Group Phureja and haploids of Group Tuberosum. Selection for adaptation to cultivation and production of 2n gametes is carried out at the diploid level, with the benefits of disomic ratios.S. chacoense provides increased genetic diversity, vegetative vigor and profuse flowering. About one-fifth of the 654 plants examined produced 2n eggs; clones with high 2n egg production may be obtained either by screening within particular introductions or by intercrossing known 2n egg producers. Only 16 of 1,212 plants screened produced 2n pollen —one by first division restitution. There is great variation among introductions and individuals for tuberization in the greenhouse. Selection for early tuberization in the field may be difficult due to extremely long stolons, but it would be facilitated by incorporation of the short stolon characteristic from the topiary mutant typeS. infundibuliforme. Male sterile Tuberosum haploids hybridize withS. chacoense to give male fertile interspecific F1 progeny, some of which produce 2n eggs or 2n pollen.