New chromosome number reports in tragacanthic Astragalus species

Abstract Cytological studies were performed in 12 populations of 10 tragacanthic Astragalus species from 3 sections of the genus Astragalus L., growing in Iran. The species of A. verus, A. caspicus, A. meyerei showed 2n = 2x = 16, A. gossypinus showed 2n = 2x = 14, A. microcephalus, A. denudatus, A. dschuparensis and A. hirticalyx showed 2n = 4x = 32, A. brachycalyx and A. compactus showed 2n = 6x = 48 chromosome number. The chromosome number of A. verus, A. caspicus, A. meyerei, A. gossypinus, A. hirticalyx, A. brachycalyx and A. compactus are new to science while, the chromosome numbers obtained for A. microcephalus and A. denudatus support the earlier studies. Only diploid and tetraploid levels have been reported in the old world thorny Astragalus species, but the occurrence of 2n = 6x = 48 in A. brachycalyx and A. compactus increases the polyploidy level occurring in this group. The species studied showed metacentric and sub-metacentric chromosomes in their karyotype. The size of chromosomes varied from 2.20 μm in A. compactus to 5.51 μm in A. hirticalyx. The species studied differed signifcantly in the size of their chromosomes and also in karyotype formulae indicating the role of quantitative and qualitative change in the chromatin (DNA) material along with polyploidy in the species diversifcation.

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