Produção e qualidade de sementes de Paspalum notatum Flügge: impactos do arranjo de plantas, do momento da colheita e do estresse hídrico durante o estágio reprodutivo

Abstract

The present work aimed to determine the appropriate time for harvesting seeds of tetraploid bahiagrass and to study factors associated with sowing (density and spacing) that would provide high seed yields in the first year of implantation, as well as to evaluate the physiological and biochemical mechanisms of this same species when exposed to water stress in the reproductive stage and its impacts on seed production and quality. The results obtained show that the implantation via sowing of 230 viable seeds allowed a high seed yield in the first year of implantation (315 kg ha-1). Seed yield in the second year after implantation was not affected by factors associated with sowing. The maturation of tetraploid bahiagrass seeds is an uneven process and the appropriate time to harvest the seeds - based on the percentage of viable seeds - can be determined from two indicators: the first is visual, which is linked to the presence of shattering in approximately 10%, while the second is a direct method, based on seed moisture, in which a percentage equal to or less than 33% should be recommended. In evaluating the impacts of water stress, diploid and tetraploid plants grew in a greenhouse under well-watered conditions until the appearance of the first inflorescences, when water deficit and excess were introduced and maintained for ten days. The photosynthetic performance of diploid and tetraploid plants was not affected by flooding. On the other hand, low water availability decreased stomatal conductance, increased leaf temperature and resulted in decreased assimilation rate of the two genotypes. The superoxide dismutase activity in the roots was similar (under flooding) and even lower (in drought) to that observed in the control plants. The roots of plants exposed to water deficit maintained an accumulation of biomass similar to that of control plants. In leaves of plants previously exposed to drought, proline was higher even in recovery. While tetraploid plants showed greater stability in reproductive characteristics, diploid plants subjected to flooding showed more inflorescences, but the total number of seeds formed per plant was reduced by drought. The results indicate that the synthesis of osmoprotectants and the activation of the antioxidant machinery are important strategies in the tolerance of bahiagrass to water stress in the reproductive phase.