| Putative hybridization between Opuntia fulgida Engelm. and O. spinosior (Engelm.) Toumey (Cactaceae, subgenus Cylindropuntia, section on Chlindropuntia) was investigated using morphometrics, cytology, pollen stainability, chemistry and embryology. That O. spinosior is a sexually normal species was supported by its normal megasporogenesis, megagemetogenesis, and embryogenesis. This was the first normal megasporogenesis reported for the genus. That O. fulgida is a largely apomictic species of low fertility was supported by its lack of normal megasporogenesis. Clustering techniques supported recognition of the hybrid entity O. Xkelvinensis Grant & Grant pro sp. (= O. kelvinensis Grant & Grant) in the study population southeast of Florence, Arizona. Chromosome counts of 160 total individuals revealed all 48 individuals of O. spinosior, both in the hybrid and control populations, to be diploid, 2x = 22. Forty-six individuals of Opuntia fulgida were diploid, while 16 were triploid. The percentage of triploids was much higher in the hybrid population than in the control population. Twenty-six individuals of O. Xkelvinensis were tripolid and only three were diploid. Percent pollen stainability was high in O. spinosior, was extremely variable in diploid O. fulgida, and was low for diploid O. xkelvinensis. All triploids had very low pollen stainability overlapping in only six cases with diploids. This information could aid in the identification of triploids for future investigations. Both morphometrics and cytology support the previous hypotheses that there are two major morphotypes of the hybrid in the population studied. These types, which have been given the genomic formulae FFS and SSF, are probably not as well defined, however, as was originally proposed. The complexity is probably a result of introgression via backcrossing of diploid O. Xkelvinensis to O. spinosior and the contamination of genes from at least one other species, O. acanthocarpa. The analysis of the alkaloid content in individuals of the hybrid population provided no supporting evidence since even the putative parents could not be distinguished. It does suggest, however, that they may be more closely related than was previously thought. |
