Karyotype analysis of bearded iris (original) (raw)

Mitra, J.

Bot Gaz 117(4): 265-293

1956

DOI: 10.2307/2473138
Accession: 024919858

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Abstract

A karyotype analysis of 40 spp., geographical races, and miscellaneous species hybrids of Iris belonging to the subgenera Eupogoniris and Pogoniris. A comparative karyotype analysis of the two dwarf diploid spp., I attica (2n = 16) and I pseudopumila (2n = 16), and the tetraploid I pumila (2n = 32), indicates that the latter is an amphidiploid of the 2 former spp. The karyotypes of the 24-chromosome dwarf species I mellita, I reichenbachii, I bosniaca. and I balkana are similar except for minor differences. Two pairs of metacentric "marker" chromosomes are found in all these spp. In the 48-chromosome dwarf species, I aphylla, and in an unidentified dwarf from the Chalcidice peninsula of northern Greece, 4 pairs of these median-constricted marker chromosomes are present, and in addition, other chromosomes are similar to those of the diploid dwarf spp. These relationships are interpreted as evidence of an autotetraploid origin of I. aphylla and of the Chalcidice dwarf. The tetraploid form of I. balkana includes some chromosomes like those of I. mellita and others like those of the diploid I balkana, suggesting an allotetraploid origin of this form. In 24-chromosome tall bearded spp., 3 different kinds of karyotypes were noted I. pallida of the Heinig collection and the diploid I. kashmiriana have 2 pairs of median-constricted marker chromosomes; other forms of I pallida, as well as I. illyrica, I. cengialti, and I. imbricata, have only 1 pair of these metacentric chromosomes. Iris variegata, I reginae, and I. perrieri have no median-constricted chromosomes. The 48-chromosome tall bearded species, I. kashmiriana, I. mesopotamica, I. cypriana, I. trojana, and I. croatica, are characterized by having 4 pairs of median-constricted chromosomes, twice the number of those present in I. pallida Heinig and the diploid I. kashmiriana. This is intepreted as evidence that these tetraploids originated from diploids of the I. pallida Heinig and I. kashimiriana type. A detailed analysis of chromosomes of both the diploid and the tetraploid I. kashmiriana indicates a possible autotetraploid origin of the tetraploid form. The occurrence of these 2 forms in the same region supports this conclusion. The 40-chromosome dwarf species, I. chamaeiris, I olbiensis, I italica, and I. benacensis, have in their somatic complement 16 chromosomes morphologically very similar to those of I. pseudopumila, and the remaining 24 chromosomes resemble those of I pallida. An amphidiploid origin of these 40-chromosome spp. from a cross between 16-chromosome dwarf spp., like I. pseudopumila, and 24-chromosome tall spp., such as I. pallida, followed by doubling, is indicated by the karyotype analysis. Similarly, a hybrid origin of 44-chromosome intermediate bearded forms from 48-chromosome tall and 40-chromosome dwarf spp. is indicated from the studies of chromosome morphology. Two distinct karyotypes were noted in the 22-chromo-some spp. belonging to the Regelia section: I arenaria and I flavissima have 2 pairs of median-constricted chromosomes, whereas I korolkowii has only 1 pair. The two 44-chromosome Regelia sp., I stolonifera and I hoogiana,have slightly different karyotypes. The 20-chromosome Oncocyclus species. I gatesii, I susiana, I lortettii, and I soforana, have exclusively chromosomes with subterminal centromeres. In various miscellaneous hybrids characteristic chromosomes of the respective parents were identified. Chromosomal heteromorphism and karyotype variation within geographical races of the same species are of frequent occurrence. The phylogenetic significance of differences in chromosome length, changes in centromere position, number of satellites, and secondary constrictions is discussed. It is suggested that chromosomal repatterning, possibly as a result of segmental interchange, inversion, or duplication, accompanied by both auto- and allotetraploidy, has played an important role in the origin of bearded iris species.