ASSIGNMENT OF ENDOSPERM BALANCE NUMBERS TO THE TUBER-BEARING SOLANUMS AND THEIR CLOSE NON-TUBER-BEARING RELATIVES

The Endosperm Balance Number (EBN) of over 80 species and subspecies of the tuber-bearing Solanums and their close non-tuber-bearing relatives representing 13 taxonomic series has been determined, with no species assigned to more than one EBN level. Among North American species, most diploids are 1EBN, most tetraploids are 2EBN and all hexaploids are 4EBN; however, among South American species most diploids are 2EBN, most tetraploids are 4EBN and again all hexaploids are 4EBN. Thus species may be isolated from others of the same ploidy level by EBN differences, e.g., 4x(2EBN) from 4x(4EBN), while other species differing in ploidy but having the same EBN may be intercrossed, e.g., 4x(2EBN) and 2x(2EBN). Chromosome doubling or 2n gametes can be used to make a lower EBN species compatible with a higher EBN species. These findings also explain the major crossing difficulties previously inherent in the use of North American species in potato improvement. They also have direct implications for potato improvement, barring the occurrence of other incompatibility barriers. Any 4x(4EBN) cultivar is endosperm compatible and thus will cross with 4x(4EBN) and 6x(4EBN) species. The 2x(2EBN) haploids of 4x(4EBN) cultivars likewise will hybridize with 2x(2EBN) and 4x(4EBN) species. All 2x(1EBN) species are crossable with 2x(2EBN) haploids through 2n gametes or chromosome doubling.