Estádios embrionários e pré-condicionamento para superação de dormência de sementes de Ilex paraguariensis A. St.-Hil. (Aquifoliaceae)

Abstract

Yerba mate seeds have embryonic dormancy due to the presence of a rudimentary embryo, in addition to the mechanical dormancy of the woody endocarp that hinders embryonic growth. In addition, dormancy is possibly linked to the origin of the matrices, and in places with a lower average temperature, the seeds need more time to develop their embryos. In this way, the work was divided into two experiments, the first aimed at characterizing the embryonic stages of six mother trees grown in Santa Maria - RS and comparing them with a matrix from Chapecó-SC. The second experiment aimed to apply seed preconditioning to accelerate the embryonic development process. In the first experiment, the seeds collected in Santa Maria and received from Chapecó, were evaluated for their biometric measurements (length, width and thickness), their weight of a thousand seeds, viability, visible embryos and embryo size, and these evaluations were made on seeds before and after stratification. In the second experiment, three factors were used, namely: pre-conditioning time (5, 10, 15 days), three levels of the solution factor (water, 0.02% KNO3 and 0.1% gibberellic acid) and four levels stratification time factor (0, 65, 140, 200 days). In the first experiment, it was observed that the seeds embryonic development was similar for all the studied mother trees, being that the number 4 mother tree was the only one to present torpedo-sized embryos. In the second experiment, the preconditioning favored germination, reaching 16% of germination in the preconditioned seeds for 15 days in 0.1% gibberellic acid and stratified for 200 days. It is concluded all the seeds of mother trees cultivated in Santa Maria - RS showed viability and percentage of visible embryos lower than the seeds of Chapecó - SC, and the embryos of the seeds of the latter did not present a more developed shape and size than the from mother tree 4 (Santa Maria - RS), which presented the most developed embryo among all mother trees. Seed pre-conditioning in 0.1% gibberellic acid for 15 days was efficient to increase the germination of yerba mate seeds after 200 days of stratification.