Cytogenetical investigations into some garden ornamentals. II. The genus Aloe L.

Abstract

Sixteen taxa belonging to ten species of Aloe were investigated. Most of these species exist only as diploids. A. arborescens was found to be tetraploid, whereas, both diploid and tetraploid individuals were studied in A. arborescens var. natalensis, A. latifolia and A. vera. Apart from unreduced gametes and hybridization, the origin of polyploidy in the genus is attributed to mitotic system as well.Split metaphases/anaphases and/or non-orientation and ultimate exclusion of some of the chromosomes accounts for aneusomatic cells (2n=9, 10, 11, 12) in A. aristata. Non-disjunction leading to unequal anaphases explains such cells in A. humilis (2n=13, 15) and A. vera (2n=15). Somatic pairing as observed in A. ferox may also result in such unequal segregations. While, the aneusomatic cells were observed in the gametic tissue as well in A. vera, their absence in the meiotic tissue in A. aristata and A. humilis indicates that these cells are not selected in the germ line.Different species presently studied, though exhibited a gross similarity in the morphology of their bimodal karyotype, differed from one another in their total chromatin length, F% and S% ratios. Satellites were observed on the long arm of large chromosomes in A. arborescens var. natalensis, A. ferox and A. vera. In A. saponaria only one chromosome of a long pair possessed satellite.Hybrid nature of the polyploid taxa in A. latifolia and A. vera is apparent, on the basis of their karyotypes. In A. arborescens, polyploidy explains meiotic abnormalities, whereas, structural heterozygosity accounts for such aberrations in A. africana, A. ferox, A. transvaalensis and A. vera (2x).