CONICET | Buscador de Institutos y Recursos Humanos

ABSTRACT. Sacoila argentina (Griseb.) Garay is a terrestrial orchid with ornamental value living at northern Argentina, Bolivia and Paraguay and is considered an object of conservation within the paraguayan Chaco region, only found at Boquerón Department and chromosomally unknown until this study. Here, we present another natural population of Sacoila argentina for Paraguay (Paraguarí Department, Villa Florida, 57º07´48.71´´W-26º23´32.16´´S) so extending its area of distribution. Conventional cytogenetic techniques were applied in order to analyze its genetic system. Sacoila argentina is a diploid species with 2n = 2x = 46 small size chromosomes (1.21 - 4.45 µm) and 40.63 µm per haploid genome. Its karyotype, composed of 38m + 8sm, is bimodal (A2=0.36/R=3.69) due to a pair (# 20, sm) more than two times larger than chromosome length mean (1.77 µm), and symmetric (A1=0.18/i=44.58/r>2=0.13) belonging to Stebbins category 2B. The chromosome pair # 20 also carry a terminal macrosatellite on the short arm with an active NOR. Sporogenesis is normal and pollen grain viability is high (80%). Meiotic behaviour is regular and chromosomes pairs as 23 bivalents in the male (pollen mother cells, PMC) as in the female meiosis (megaspore mother cells, MMCs), confirming the basic number x = 23 for Sacoila. In PMCs and MMCs at diakinesis/metaphase I, ring bivalents (80%) with distal chiasmata (85%) are common and the mean of chiasmata per bivalent is high (1.80) in both germinal lines. The recombination index, afected by the meiotic number (n = 23) and the mean of chiasmata/cell (41.5) is high (RI=64.5). Natural populations of Sacoila argentina possess low density, are scarce, interspersed and just found at flowering time, for these reasons is a rarely collected species.

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