Estabilidade genética, perfil de óleo essencial e morfologia em poliploides sintéticos de Lippia alba (Mill) N. E. Brown (Verbenaceae)

Abstract

Polyploidy is considered to be one of the main mechanisms related to evolution and speciation in plants. Its presence is often associated with the evolutionary success of these individuals. Lippia alba (Mill.) NE Brown (Verbenaceae) is a species of medicinal plant that is widely distributed throughout South America. Previous studies have revealed that this species constitutes a polyploid complex with five distinct chromosome numbers, making it an interesting tropical polyploid model for studies involving plant evolution. Synthetic polyploidy provides a better understanding of the biological processes related to polyploidization. The aim of this study was to induce polyploidy in diploid (2x=30) and triploid (3x=45) accessions of L. alba, to evaluate the genetic stability of the polyploids obtained over time and analyze the morphological differences between these accessions. First, a pilot experiment was carried out, testing 5 concentrations and 2 different exposure times for colchicine - from this, 1 concentration and 2 exposure times were selected for the next experiments. In these experiments, 100 explants were exposed in vitro to colchicine at a concentration of 0.2% for 4 and 6 hours. To assess the survival rate, analyses were carried out from the 20th day after exposure and repeated every 10 days until 60 days had elapsed. At the end of this period, the amounts of DNA were estimated via flow cytometry to check the level of ploidy. In addition, the ploidy level was assessed every 30 days to monitor the genetic stability of these plants. In all the accessions, there was a significant difference in the survival rate of the treatments compared to the control group. At the end of the experiment, the diploid accessions were responsible for the largest generation of mixoploids and polyploids. The only acquired hexaploid experienced a drop in its DNA quantity over time, presenting itself as a mixoploid after 90 days and remaining so until the last analysis. For the surviving tetraploid and synthetic mixoploid accessions, exposure to colchicine did not generate significant results for all the morphological parameters evaluated, only in the measurements of root, stem and leaf area. With regard to the essential oil profile, the patterns observed in the synthetic polyploids were the same as those already reported in other studies on the species, with triploids showing a higher composition of linalool and diploids and tetraploids higher amounts of citral. The results obtained in this study contributed to a better understanding of the process of inducing polyploidy in the Lippia alba species, as well as to optimizing the protocol for inducing synthetic materials. In addition, the polyploids and mixoploids generated will be of great value for comparative studies between ploidies and for understanding the evolution of the genome in the species.