Biologia e estrutura floral em acessos de Adenium obesum

Abstract

Adenium obesum, popularly known as desert rose, has become a valuable option for the ornamental plants sector. In floriculture, the production of hybrids is prioritized, for this, knowledge of the floral biology of the species is essential. Considering the lack of scientific data related to the species, mainly in Brazilian semi-arid environments, the objective of this study was to relate the ornamental potential of the species with (1) the floral events and the morphology; (2) the anatomy of flowers and (3) viability of pollen grains and stigmatic receptivity in three accessions of Adenium obesum. The design used for the experiments was completely randomized. For the analysis of pollen viability and stigmatic receptivity, a 3x3 factorial scheme was used, with three stages of flower collection (pre-anthesis, anthesis and post anthesis) and three accesses (ICA-rs, ICA-bd and ICA-vt), with four repetitions for pollen viability and five repetitions for stigmatic receptivity. A. obesum blooms all year and the flowers open in the morning. The ICA-vt access showed a longer development period (32.29 days) between the initial phase of the flower bud and anthesis compared to ICA-rs and ICA-bd, which did not differ statistically. There was a significant variation between the materials, indicating a great phenotypic diversity for Adenium obesum. The flowers of the three accessions of A. obesum studied were organized in terminal inflorescences and are generally slightly zygomorphic, pentameric and bisexual. Total and partial sterility of androceu and the changes in its appendages are aspects previously unknown. The ICA-vt access presented the largest dimensions of length and diameter of the floral tube and diameter of the open corolla. An additional layer of petals, small and more internal to the three whorls observed in general, appeared in the ICA-vt access. The potential of ICA-vt access was revealed by the morphological, morphometric, and floral longevity aspects for floriculture. The accesses ICA-rs and ICA-bd are similar in terms of gynecium aspects. Divergences were found in relation to the gynecium of the ICA-vt access, as to its vascularization, the number of stamens and the appearance of a structure with secretory portion in the ICA-vt access. Anatomical analysis revealed phenotypic diversity in A. obesum, mainly regarding Organs reproductive organs. Morphological variation in the stylus head of ICA-vt samples was found. Different levels and types of male sterility were recorded, as well as a tendency to decrease female fertility in some samples of ICA-vt. Morphological markers associated with the different stages of the sporogenesis and gametogenesis processes were determined. The access ICA-bd stood out and can be considered as a pollen donor in artificial pollinations. The germination rate of pollen grains was significantly higher for ICA-bd in all analyzed phases. The stigma of A. obesum flowers were receptive from one day before the opening of the flowers to three days after the flower opened, with no difference between accessions. These results may support several new studies in the fields of applied botany, genetics and plant breeding aiming at the development of new materials that meet the requirements of producers and consumers.