Mecanismo de superação da dormência em sementes de Urochloa (Syn. Brachiaria)

Abstract

The physiological dormancy of seeds of the genus Urochloa makes their commercialization difficult. In this study, it was evaluated whether freshly harvested seeds of cultivars of the genus Urochloa with different levels of dormancy are sensitive to abscisic acid (ABA), gibberellins (GA) and their respective biosynthetic inhibitors [fluridone (FLU) and paclobutrazol] and whether this sensitivity is overcome during after-ripening in the laboratory environment and in the seed bank in the soil. In seeds of cultivars there were different levels of sensitivity to exogenous regulators and inhibitors, depending on the treatment and concentration used, germinative characteristics were influenced. In addition, during after-ripening in a laboratory environment, the seeds of the Cayana and Sabiá cultivars remained sensitive to ABA up to 131 days, whereas for the Marandu cultivar this occurred only in period 0 of after-ripening. For seedling vigor, it was observed that FLU applied to seeds negatively affects pigment content, regardless of cultivars and period analyzed. It was found that the cultivars do not acquire secondary dormancy in the seed bank in the soil. It was concluded that the physiological dormancy of the seeds of the tested cultivars is maintained by the sensitivity of seeds to ABA for the tested cultivars, so this sensitivity is the main impediment to germination. Treatments with GA, FLU and Pro-Gibb® did not promote the germination of seeds stored in a laboratory environment, and this after-ripening reduced the sensitivity of seeds to ABA, thus promoting germination. FLU negatively influences the photosynthetic pigment content of seedlings of the genus Urochloa and seed dormancy in the studied cultivars is innate.