The endosperm balance number (EBN) hypothesis, as a classification of effective ploidy, is imperfect. Research since its initial proposal in 1980 has highlighted both its utility and inconsistencies. It is clear that the genetic mechanisms than govern effectively ploidy are complex and genome wide, suggesting that variation should exist in between species within each EBN category. This is supported by data generated at Michigan State University on the efficiency of S. verrucosum bridge crosses with 12 1EBN species across 18 plant introductions. This new information challenges our previous knowledge on what species are accessible to potato breeders, and through repeated measurements we have been able to identify how difficult/easily certain species can be accessed. Further research will focus on establishing the significant difference in bridging ability between S. verrucosum clones, to determine if clones with higher efficiency can be selected for.