Indução de poliploidia em Oncidium crispum

Abstract

The production of polyploids by artificial means has been widely used in plant breeding programs and is considered advantageous from genetic, agronomic, and evolutionary perspectives. In most cases, induced chromosome doubling promotes the expansion of available gene combinations, resulting in increased genetic variability and enabling the emergence of phenotypes with agronomically desirable traits. Artificial polyploidization is, therefore, a strategic tool in the development of new cultivars with added commercial value, especially in the ornamental sector. This study aimed to induce and comparatively characterize artificial polyploids in Oncidium crispum using in vitro treatments with two concentrations (0.05% and 0.1%) of colchicine for periods of 4 and 7 days. Polyploidy induction was evaluated using cytogenetic techniques, including classical chromosome counting with the fluorochrome DAPI and flow cytometry to estimate genomic content. Control individuals had 58 chromosomes and an average of 3.58 pg of DNA, while induced polyploids had 116 chromosomes and approximately 6.76 pg of DNA. Furthermore, a comparative analysis of the DNA methylation pattern between diploid, polyploid, and mixoploid plants was performed using methylation-sensitive enzymes and ISSR markers (MS-ISSR). The results indicated that internal DNA cytosine methylation was absent in diploids but present in polyploids and mixoploids, while external cytosine methylation was observed only in diploids, suggesting a significant modification in the epigenetic profile resulting from genome duplication. There was no statistically significant difference in total methylation between diploids and polyploids. This study reinforces the feasibility of inducing polyploidy in O. crispum for ornamental breeding purposes and highlights the importance of integrated cytogenetic and epigenetic analyses for understanding the molecular consequences of polyploidy in ornamental plants.