Julio R. Daviña

Chromosome studies in Orchidaceae from Argentina

The center of diversity of Argentinean orchids is in the northeast region of the country. Chromosome numbers and karyotype features of 43 species belonging to 28 genera are presented here. Five chromosome records are the first ones at the genus level; these taxa are Aspidogyne kuckzinskii (2n = 42), Eurystyles actinosophila (2n = 56), Skeptrostachys paraguayensis (2n = 46), Stigmatosema polyaden (2n = 40) and Zygostates alleniana (2n = 54). In addition, a chromosome number is presented for the first time for 15 species: Corymborkis flava (2n = 56), Cyclopogon callophyllus (2n = 28), C. oliganthus (2n = 64), Cyrtopodium hatschbachii (2n = 46), C. palmifrons (2n = 46), Galeandra beyrichii (2n = 54), Habenaria bractescens (2n = 44), Oncidium edwallii (2n = 42), O. fimbriatum (2n = 56), O. pubes (2n = 84), O. riograndense (2n = 56), Pelexia ekmanii (2n = 46), P. lindmanii (2n = 46) and Warrea warreana (2n = 48). For Oncidium longicornu (2n = 42), O. divaricatum (2n = 56) and Sarcoglottis fasciculata (2n = 46+1B?, 46+3B?), a new cytotype was found. Chromosome data support phylogenetic relationships proposed by previous cytological, morphologic and molecular analyses, and in all the cases cover some gaps in the South American literature on orchid chromosomes.

Comparative cytogenetics in Cyclopogon (Orchidaceae)

A cytotaxonomical description of Cyclopogon (Spiranthinae, Orchidaceae) is carried out through a deep karyotype analysis of four species from NE Argentina. Distinctive karyotype parameters concerning the chromosomes number, morphology, size and symmetry and the genome size associate to each taxon. Cyclopogon calophyllus (2n = 2x =28; 18m + 10sm), C. congestus (2n = 2x = 32; 26m + 6sm), C. elatus (2n = 2x = 28; 18m + 10sm) and C. oliganthus (2n = 4x = 64; 40m + 24sm) possess symmetrical karyotypes (i-mean = 40.01–42.84; A1 = 0.24–032; r>2 = 0.06–0.29) and excluding C. congestus (A2 = 0.26; R = 2.62) unimodality is the rule (A2 = 0.12–0.20; R = 1.73–1.92). Diploid taxa show a terminal macrosatellite in the m pair no. 2 (large arm) and share a comparable mean chromosome length (ca. 2.75 μm) and genome size (ca. 40 μm), superior to the tetraploid C. oliganthus (ca. 2 and 32 μm, respectively). The novel data added to preceding cytological, morphological and molecular approaches involving Cyclopogon and those related taxa of Spiranthinae largely based on x = 23 support the hypothesis that the unusual 2n and the karyotype morphology of Cyclopogon is an evolutionary advance within Spiranthinae with a basic reduction to x = 14 or 16 by chromosome fusions. A polyploid-dysploid series added to dibasic hybridization explain the extant 2n diversity though a paleopolyploid series on x = 7–8 is also possible.

Cytotaxonomy of Tripogandra diuretica and Tripogandra glandulosa (Commelinaceae) from NE Argentina

Abstract Karyotype features and microsporogenesis of Tripogandra diuretica (Mart.) Handlos and Tripogandra glandulosa (Seub.) Rohw. from 15 NE Argentina accessions are analysed via classical cytogenetics, CMA/DA/DAPI and Ag-NOR. The karyotype of T. glandulosa (2n = 2x = 16; 2m + 6sm + 8st) is bimodal (A 2 = 0.37; R = 2.65) and asymmetrical (A 1 = 0.63; i = 26.06; r > 2 = 0.88) (3B-Stebbins) with a genome size of 33.28 μm; two pairs are satellited, CMA+ and NOR-actives. Another four CMA+ loci and DAPI+ universal centromeric heterochromatin occur. Microsporogenesis is normal (pollen viability short stamens = 97.8%; large = 96.7%), meiotic behaviour is regular and chromosomes pair as 8II. The karyotype of T. diuretica (2n = 8x = 64; 8m + 24sm + 32st) is bimodal (A 2 = 0.27; R = 2.54) and asymmetrical (A 1 = 0.60; i = 27.32; r > 2 = 0.88) (3B-Stebbins); additionally, two pairs are satellited. Microsporogenesis is normal (short stamens = 77.8%; large = 68.5%), except for micronuclei and low pollen viability in some accessions. Meiotic behaviour is regular with 32II, acting as a cytological diploid, however the arrangement of the haploid karyotype suggests that T. diuretica, which also exhibits a reduction of the genome size (18.58 μm), constitutes an auto-octoploid taxa. Additionally, both species share cytological features common to karyotype orthoselection.

Estudios cromosómicos en Acmella bellidioides (Sm.) R.K.Jansen (Asteraceae) del nordeste de Argentina

Acmella bellidioides es una hierba perenne pequena, que crece naturalmente en las provincias del nordeste de Argentina, en Brasil, Paraguay y Uruguay. Pertenece a la seccion Megaglottis, presenta numero cromosomico gametico n = 13 y exhibe un amplio rango de variacion morfologica que ha hecho dificil separarla de especies muy cercanas de la misma seccion. Acmella bellidioides fue coleccionada en campos abiertos, de suelo arenoso y rocoso y se aplicaron tecnicas citogeneticas convencionales para analizar sus cromosomas en mitosis, su comportamiento en la microsporogenesis y para confeccionar su cariotipo. Acmella bellidioides es diploide con 2n = 2x = 26 cromosomas de tamano pequeno (2,22 - 4,01µm) y 39,25 µm/genoma. Su cariotipo, 12m + 10sm + 4st, es unimodal (A2 = 0,16 / R = 1,80) y levemente asimetrico (A1 = 0,42 / i = 35,88 / r>2 = 0,54 / AI = 3,69) (Categoria 3A de Stebbins). El par 9 (sm) presenta un macrosatelite terminal y constriccion secundaria en el brazo corto. La microsporogenesis es normal y produce polen viable (>90%). El comportamiento meiotico es regular. En CMP en diacinesis y metafase I se observan 13 bivalentes. Este es el primer estudio cariotipico en Acmella. Nuestro registro de 2n = 2x = 26 cromosomas coincide con el numero basico x = 13 propuesto para el genero y para Megaglottis, la seccion mas ancestral. Por lo tanto, esta es la descripcion del cariotipo basico de Acmella.