In the first part of the thesis, experiments are described where self-compatible tetraploids of L. peruvianum were isolated from tissue culture and the expression and inheritance of their S-related proteins was explored. The S-related protein profiles of styles of self-compatible tetraploids were indistinguishable from the diploid self-incompatible explant source based on SDS-PAGE. Progenies obtained from self-fertilization of two tetraploids were all found to be self-compatible. Cloned cDNA sequences of the S-related proteins were used to determine the inheritance at the locus in these progenies through Southern hybridization. The allelic ratio consistent with the predicted ratio obtained if only the pollen bearing two different alleles was successful in achieving fertilization. This work demonstrates that the observed self-compatibility in the tetraploids was due to failure of recognition of heterogenic pollen by the style, while the expression and activity of the S-related stylar proteins remained unaffected. In the second part of the thesis, periclinal chimeras between the SI L. peruvianum (P) and the SC L. esculentum (E) were utilized to analyze the relative influence of apical cell layers as they relate to SI and Unilateral incompatibility (UI). Irrespective of the expression of S-proteins in the chimeral styles, the chimeras were compatible with P component indicating that there was failure of recognition of the "self" pollen (the chimeras and the P component are genetically similar at the S-locus). The breakdown of SI was not related to the RNase activity of the S-proteins which was intact in all chimeras. Therefore S-proteins are not sufficient to maintain the SI response. Since the response was lost if either of the two layers (L1 and L2) was composed of E component, we conclude that both L1 and L2 are required for the SI phenotype. On the other hand, UI response was maintained in all the chimeras in which the L1 or L2 layer was P. This seems to suggest that SI and UI responses are developmentally unrelated in these chimeras.

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.