Inheritance and Linkage Relationships of Isozymes in Easter Cactus

Polyacrylamide gel electrophoresis was used to study inheritance and linkage of isozymes in Easter cactus ( Hatiora species and interspecific hybrids). Five isozyme systems were analyzed: aspartate aminotransferase (AAT), glucose-6-phosphate isomerase (GPI), malate dehydrogenase (MDH), phosphoglucomutase (PGM), and triosephosphate isomerase (TPI). F 1 , F 2 , BC 1 , and S 1 progeny were used for inheritance studies. Six polymorphic loci ( Aat-1, Gpi-1, Mdh-1, Pgm-1, Pgm-2 , and Tpi-2 ) were identified. Aat-1 and Pgm-1 were linked (recombination frequency = 26% ± 7%), but the other isozyme loci assorted independently. Aberrant segregation ratios were observed in at least one segregating family for all six isozyme loci. We hypothesize that segregation distortion was due to linkage between isozyme loci and other genes subject to pre- or postzygotic selection. The existence of five additional isozyme loci ( Aat-2, Gpi-2, Mdh-2, Mdh-3 , and Tpi-1 ) was inferred from segregation patterns and by comparison of isozyme profiles from phylloclades and pollen. These isozyme loci may prove useful for confirming hybridity in intra- and interspecific crosses, determining parentage of cultivars, and assessing genetic diversity in germplasm collections.