Mecanismos de Evolução Cariotípica em Epidendrum L. (Orchidaceae: Epidendroideae)

The genus Epidendrum L. comprises approximately 1,500 species of exclusively neotropical distribution, with frequent occurrence of hybridization, polyploidy and asexual reproduction. In addition, some species show complex taxonomy, such as E. secundum, which shows extensive chromosome number variation. This study aimed to test the hypotheses about the causes of chromosome number variability in E. secundum; to investigate the hybrid origin in representatives with intermediate floral morphology between E. flammeum x E. secundum, and between E. xanthinum x E. secundum; and to analyze the heterochromatin diversity and DNA content in species belonging to the subgenus Amphiglottium and Epidendrum. To this end, we performed the quantification of nuclear DNA content by flow cytometry, analysed the heterochromatin distribution using CMA/DAPI fluorochrome banding, and performed the analysis of floral morphology on representatives found in hybridization zones. Mitotic analyzes showed different chromosome counts ranging from 2n = 24 in E. fulgens to 2n = 224 in E. cinnabarinum, with metacentric, submetacentric and acrocentric chromosomes in all species. CMA+/DAPI¬ pericentromeric and terminal chromosome regions, and some CMA¬/DAPI+ and CMA0 terminal regions were identified, with variation in size, number and position. Pericentromeric regions generally was CMA0/DAPI¬ in most species. The leaf tissues of all specimens examined presented one or two endoreduplication cycles. To 18 populations of E. secundum analyzed, 16 presented diploid individuals, with an average of 2C = 4.08 pg DNA, and in two populations were identified tetraploid individuals, with an average of 2C = 8.24 pg DNA. In some populations were identified cytotypes with B chromosomes in variable number, sometimes entirely CMA+/DAPI¬. In relation to putative hybrid analysis, three hybrid zones were investigated. In São João do Tigre (PB), E. flammeum presented 2n = 50 and 2C = 5.04 pg DNA, E. secundum presented 2n = 62 chromosomes and 2C = 4.82 pg DNA. Hybrid ...