CONICET | Buscador de Institutos y Recursos Humanos

Background and aims: Zephyranthes mesochloa, is a bulb species with white flowers that inhabits the subtropical regions of South America and presents different chromosome numbers. Different chromosome numbers have been reported for this species. The aim of this work is to perform chromosome analysis of specimens of Z. mesochloa from northern Argentina, in order to contribute to cytogenetic knowledge of the genus.M & M: Ploidy levels and somatic chromosome numbers were determined in individuals belonging to 8 populations from northern Argentina using conventional staining. In addition, meiotic preparations with acetic carmine in one of the individuals, were made.Results: Seventy five percent of the populations were diploid, with 2n = 2x = 12 with a karyotypic formula 4m + 4sm + 4st. In two of the diploid populations, individuals with 2n = 13 were observed. These individuals presented an additional metacentric chromosome, a B chromosome. Analysis of diakinesis and metaphase I of aneuploid plants microsporogenesis (2n = 13) showed 6 bivalents and 1 univalent in all pollen mother cells (PMCs) analyzed. The remaining populations (25%) were tetraploids with 2n = 4x = 24 and a karyotypic formula 8m + 8sm + 8st. Geographically, the distribution of Z. mesochloa cytotypes are discontinuous, without sympatric or adjacent combinations.Conclusions: The duplicate karyotype formula in tetraploids regarding its con-specific diploids and the high morphological identity between the 2x and 4x accessions, indicate that the origin of an autopolyploid cytotype. The available data allows us to consider the group of cytotypes as part of a polyploid complex with a basic number of x = 6.

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