Isozyme polymorphism and inheritance in Hatiora and Schlumbergera (Cactaceae)

Isozyme analysis was used to identify clones, measure levels of genetic variation within groups of clones, and analyze mating systems in two Cactaceae genera--Hatiora and Schlumbergera. Isozymes were extracted from phylloclades and pollen and were separated by polyacrylamide gel electrophoresis. The inheritance of aspartate aminotransferase (AAT), glucose-6-phosphate isomerase (GPI), malate dehydrogenase (MDH), phosphoglucomutase (PGM), and triosephosphate isomerase (TPI) was examined in Hatiora. Six loci (Aat-1, Gpi-1, Mdh-1, Pgm-1, Pgm-2, and Tpi-2) were analyzed, and results were generally as expected for single loci with codominant alleles. For all six isozyme loci segregation distortion was observed in at least one segregating family. Aat-1 was linked with Pgm-1 (26 cM), but the other isozyme loci assorted independently. The inheritance of leucine aminopeptidase (LAP), phosphoglucomutase (PGM), and shikimate dehydrogenase (SKD) was investigated in Schlumbergera. Three loci were analyzed (Lap-1, Pgm-1, and Skd-1), and results were generally as expected for single loci with codominant alleles. Significant segregation distortion was observed in at least one segregating family for all three isozyme loci. Disturbed segregation at Lap-1 was due to tight linkage (7 cM) with the locus controlling gametophytic self-incompatibility (S). All three loci assorted independently of each other. In a third study, a Hatiora germplasm collection composed of 49 clones was assayed for AAT, GPI, LAP, MDH, PGM, SKD, and TPI. Thirteen putative loci and 42 putative alleles were identified, and 9 of the 13 loci (69%) were polymorphic. Twenty-two clones (45%) could be distinguished solely on the basis of their isozyme profiles, but the other 27 clones shared isozyme profiles with one to five other clones. Thirteen modern H. x graeseri cultivars exhibited less genetic diversity than 40 H. gaertneri, H. x graeseri, and H. rosea clones representing older and modern cultivars plus field-collected specimens. The difference in genetic diversity was primarily attributed to a loss of alleles during breeding. In a fourth study, a Schlumbergera germplasm collection composed of 59 clones was assayed for AAT, GPI, LAP, MDH, PGM, SKD, and TPI. Twelve putative loci and 36 putative alleles were identified, and 10 of the 12 loci (83%) were polymorphic. Forty-one clones (69%) could be distinguished solely on the basis of their isozyme profiles, but the other 18 clones shared isozyme profiles with one or two other clones. Forty-two commercial clones of S. truncata, S. x buckleyi, and S. x exotica exhibited less genetic diversity than 14 field-collected clones of S. kautskyi, S. opuntioides, S. orssichiana, S. russelliana, and S. truncata. The difference in genetic diversity was attributed to limited sampling from wild populations and loss of alleles during breeding