Cytogenetics and cytotaxonomy of some Brazilian species of Cymbidioid orchids

Abstract

The Cymbidioid phylad presents the widest chromosome number variation among orchids, with records varying from 2n = 10 in Psygmorchis pusilla to 2n = 168 in two species of Oncidium. In the present work, a total of 44 species were studied belonging to 20 Cymbidioid genera, as a contribution to clarifying the karyological evolution of the group. All the plants investigated were collected in Brazil, mainly in the northeast region. The chromosome variation found was similar to that previously registered in the literature. Chromosome numbers observed were: 2n = 54 (subtribe Eulophiinae), 2n = 44, 46, 92 (subtribe Cyrtopodiinae), 2n = 54, ca. 108 (subtribe Catasetinae), 2n = 52, ca. 96 (subtribe Zygopetalinae), 2n = 40, 80 (subtribe Lycastinae), 2n = 40, 42 (subtribe Maxillariinae), 2n = 40 (subtribe Stanhopeinae), 2n = 56 (subtribe Ornithocephalinae), and 2n = 12, 20, 30, 36, 42, 44, 56, 112, ca. 168 (subtribe Oncidiinae). Interphase nuclei varied widely from simple chromocenter to complex chromocenter types, with no apparent cytotaxonomic value. In the genera Catasetum and Oncidium, the terrestrial and lithophytic species presented higher ploidy levels than the epiphytic species, suggesting a higher adaptability of the polyploids to those habitats. The primary base number x = 7 seems to be associated to the haploid chromosome numbers of most Cymbidioid groups, although n = 7 was observed only in two extant genera of Oncidiinae. For each tribe, subtribe and genus the probable base numbers were discussed along with the possible relationships to the primary base number x 1 = 7 admitted for the whole phylad.

Heterochromatin diversity and its co-localization with 5S and 45S rDNA sites in chromosomes of four Maxillaria species (Orchidaceae)

“…three species with 2n = 40 and three with 2n = 42 . Similarly, most better-studied orchid genera, such as the horticulturally important genera Laelia and Cattleya, show little variation in their chromosome numbers (see Felix and Guerra, 2000;. However, our analysis with base-specific fluorochromes showed more pronounced karyological differentiation among the four Maxillaria species, including variation in the number and location of heterochromatic bands with both CMA and DAPI staining.…”

Cytogenetic and cytometric analyses in artificial intercytotypic hybrids of the emergent orchid model species Erycina pusilla

“…The variation in genome size causes no difference in gene number, but does cause divergence in the quantity of repetitive DNA sequences (Flavell et al 1974(Flavell et al , 1977Leitch et al 2009). E. pusilla is placed in the Cymbidioid group, which suggested that the most probable basic chromosome number for this group is x = 7 (Felix and Guerra 2000. Moreover, the haploid chromosome number in the genus Erycina, previously called Psygmorchis Dodson and Dressler, was found to vary between 2n = 10, 12 and 14 (Felix and Guerra 2000).…”

“…E. pusilla is placed in the Cymbidioid group, which suggested that the most probable basic chromosome number for this group is x = 7 (Felix and Guerra 2000. Moreover, the haploid chromosome number in the genus Erycina, previously called Psygmorchis Dodson and Dressler, was found to vary between 2n = 10, 12 and 14 (Felix and Guerra 2000). Therefore, the change in chromosome number is apparently from 12 to 10, and possibly initially from 14.…”

“…Karyotype analysis in the Orchidaceae revealed a wide range of chromosome numbers, and this diversity has been employed to evaluate evolutionary relationships and taxonomic divisions (Felix and Guerra 2000. E. pusilla has several advantageous features, such as a relatively small genome size (1.5 pg/1C, Chase et al 2005), low chromosome number (2n = 10, Felix and Guerra 2000or 2n = 12, Felix and Guerra 1999, short generation time (less than 1 year), tiny adult plant (less than 10 cm in height at maturity) and all year blooming, which makes it a good potential model species in the Orchidaceae, one of the largest flowering families. However, variable chromosome complements of 2n = 10 and 2n = 12 are reported for this species, and it is rare for a species to present more than one cytotype.…”

Two reported cytotypes of the emergent orchid model species Erycina pusilla are two different species

“…For example, the basic chromosome number of Paphiopedilum was proposed as 2n = 26, and the chromosome number variation under the genus ranged from 2n = 26-42 caused by a Robertsonian centric fission mechanism (Jones 1998;Lee et al 2011). It has been proposed that the change in chromosome number is from 12 to 10, even initially from 14, in this species (Yeh et al 2015) because E. pusilla is in the Cymbidioid group, in which the most probable basic chromosome number is x = 7 (Félix and Guerra 2000. In this study, we have demonstrated divergent chromosome profiles between two karyotypes that are mostly likely due to multiple steps in chromosome rearrangements.…”