Parâmetros para poliploidização in vitro de Adenium obesum: contribuições para o melhoramento de plantas ornamentais

Abstract

Adenium obesum, popularly known as desert rose, is a highly attractive ornamental plant due to its morphological characteristics and economic potential. Optimizing protocols for polyploid induction requires establishing the type of explant, the type of chemical agent, the concentration of antimitotics, and the exposure time. Conversely, studies related to seed structure and endosperm tissue formation are important for better understanding and identification of the species, as well as assisting in germination processes and genetic improvement. Therefore, this thesis was divided into two articles with the following objectives: to establish an in vitro regeneration system for the production of polyploid plants using antimitotics in A. obesum to improve the vegetative and floral attributes of the species, and to identify the structure of the seed and endosperm tissues in A. obesum. For article 1, the following procedures were followed: in trial 1, in a factorial design (3x3x3+1), three types of explants (apical, medial, and basal) were evaluated, subjected to three concentrations of colchicine (0.01%, 0.05%, and 0.1%) + 0% at different exposure times (6h, 12h, and 18h). In trial 2, also in a factorial design (3x2 +1), shoot apices were subjected to three concentrations of colchicine (0.001%, 0.005%, and 0.01%) + 0%, at different exposure times (9h and 12h). In trial 1, it was observed that explants from the apical and medial regions showed the highest survival rates, especially during the longer exposure periods. Sprouting occurred at 6 and 12h intervals. In trial 2, the results were significant only in the oxidation characteristic. In the same study, flow cytometry analyses showed high polyploidization in explants from the apical region at concentrations of 0.001%, 0.005%, and 0.01% for 9 hours, in addition to those exposed to 0.01% for 12 hours. For the second article, the anatomical results reveal that A. obesum presents anatropous, unitegumented, and tenuinucellate ovules, formed by a tegument, nucellus, and embryo sac. Eight days after pollination (DAP), it was possible to observe a voluminous cell with a central vacuole, peripheral cytoplasm, and multinucleation, characterizing the primary endosperm cell. At 40 DAP, endosperm cellularization was complete, and the embryo could be observed. The seed is formed by a tegument, storage tissue, and embryo. Therefore, we conclude that it was possible to induce polyploidy in A. obesum through the optimization of protocols that indicated the apical region and the 9h time with greater efficiency. In parallel, anatomical studies of the seeds and their endospermic tissues are fundamental for a better understanding of embryonic development, since little is still known about the species, in addition to providing, with these studies, an understanding of the dynamics of germination and seedling development.