Abstract
Abstract Plants of Opuntia cochinera, O. hyptiacantha, and O. streptacantha species, collected in the Valley of Mexico, were consistently octoploids with a chromosome number 2n=8x=88, confirming a base chromosome number x=11 for the genus Opuntia. Karyotypes of the three species were homogeneous with 88 metacentric chromosomes. Interspecific variation of the genome was shown in chromosome size, genome length and chromosomes with satellites. The smallest chromosomes were found in O. hyptiacantha (1.07-2.50 μm), the intermediate size in O. cochinera (1.19-2.71 μm) and the largest in O. streptacantha (1.55-3.57 μm). Genome length was as follow: O. hyptiacantha had the smallest value (152.49 μm), O. cochinera an intermediate value (166.79 μm), and O. streptacantha the longest (210.99 μm). Opuntia cochinera presented 16 chromosomes with a satellite, this fact suggested an auto-octoploid origin. There were 6 chromosomes with a satellite in O. hyptiacantha and 20 in O. streptacantha, it indicated that both species had an allooctoploid origin; so it is possible to call these Opuntia species with genomes of partial homology.
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