Boro e manejo de crescimento das plantas nos componentes de rendimento e qualidade sementes de Brachiaria brizantha cv. BRS Paiaguás

Abstract

The production of tropical forage seeds has been based on the basic knowledge of producers, as there is a lack of available and accessible results on the management of these fields. The uniformization and fertilization of the forage plants can increase the productivity and the quality of seeds of Brachiaria brizantha. In this context, the objective was to evaluate the management of plant growth, through uniformization cuts, and the application of boron doses, in the productivity and seed quality of Brachiaria brizantha cv. BRS Paiaguás. The trial was conducted at Embrapa Gado de Corte, in Campo Grande-MS, in the harvest 2018/19. Growth management was carried out on 01/11 (67 days after sowing - DAS) and 01/25/2019 (81 DAS) and, as a control, free-growing plants (SEM) were used. Boron was applied on the leaves at the beginning of floral differentiation, at doses 0, 1, 2, 4 and 8 kg ha-1, as boric acid. It was evaluated the period between onset and full flowering, maximum number of inflorescences, chlorophyll (SPAD unit), quantity and viability of pollen grains, total seed and pure seed productivity, percentage of pure seeds, percentage of number of full and empty seeds, weight of a thousand seeds, viability by the tetrazolium test, electrical conductivity, germination pattern, first and second germination count and germination speed index. The trial was conducted in a randomized block design, with four replications, in a 3x5 factorial arrangement (growth management x boron doses). The data were submitted to analysis of variance by the F test, with comparison of means by the Tukey test (5%), using the statistical programs R version 3.6.0 and SAS version 9.3. Uniformization management interfered with the forage cycle, increasing the period between sowing and harvesting by up to 40 days in relation to free-growing plants. The onset of flowering occurred, on average, 18 days after the start of differentiation in reproductive tillers and full flowering occurred five days after the beginning of flowering, for all growth management. The full flowering (PF) of the plants occurred on 30/01, 15/02 and 25/02/2019 and the harvest of the seeds in the inflorescences (bunch) on 07/03 (30 days after PF), 26/03 (34 days after PF) and 04/16/2019 (45 days after PF), respectively for SEM management, 67 DAS and 81 DAS. None of the treatments showed a difference in terms of chlorophyll content by the SPAD unit. The number and viability of pollen grains per anther were higher when the plants were kept in free growth. The management of growth by uniformization provided an increase in seed productivity by up to 355%. When carried out at 81 DAS, it resulted in the highest productivity of pure seeds, of 90.9 kg ha-1, as well as the highest weight of a thousand seeds, of 5.8 g, followed by manegement at 67 DAS and SEM, with yields being , respectively, 55.7 kg ha-1 and 26.9 kg ha-1. Seeds from plants uniformized at 81 DAS showed a higher percentage of germination in the second count and a higher rate of germination speed, being of the better quality than those of the other treatments. The electrical conductivity varied in relation to growth management and uniformization at 67 DAS provided the greatest seed vigor. The treatments did not influence the seeds viability and, when compared with the standard germination test, it was possible to verify the presence of dormancy. Thus, it was concluded that application of boron to shoot of B. brizantha cv. BRS Paiaguás, at the beginning of floral differentiation, did not influence the variables evaluated, either alone or in combination with the uniformization managements. The growth uniformization applied at 81 DAS provided an increase in the forage cycle, prolonged the flowering period, increased the productivity of pure seeds and the weight of a thousand seeds, resulting in a higher rate of germination speed.