Ácido ascórbico na qualidade fisiológica de sementes de capim-marandu em condições hídricas e térmicas

Abstract

The use of techniques capable of stimulating the performance of seeds and seedlings, especially in adverse conditions, are extremely important for the provision of an adequate seedling stand, determining the establishment of the crop. Thus, the objective of the present work was to evaluate the physiological quality of seeds of marandu grass submitted to ascorbic acid doses and exposed to different water and thermal conditions. For this, two experiments were installed, both in a completely randomized design, using four replicates per treatment, and conducted in a 3x5 factorial scheme. The first consisted of submitting the seeds to three osmotic potentials obtained with polyethylene glycol 6000 solutions (0; -0.2 and -0.4 MPa) depending on their conditioning in five doses of ascorbic acid (0; 20; 40; 60 and 80 mM). The following physiological analyzes were then performed: germination, root protrusion, first germination count, germination speed index, root length and seedling shoot. The second experiment involved exposing the seeds to three temperature conditions (20; 35 and 20-35 °C) by conditioning with five doses of ascorbic acid (0; 20; 40; 60 and 80 mM). Therefore, the germination percentages, first germination count, as well as the germination speed index, root length and seedling length were evaluated. The data were subjected to analysis of variance, and the means of both osmotic potentials and temperatures were compared by Tukey's test (P<0,05), while the results from ascorbic acid doses were subjected to analysis of regression. The osmotic potentials influenced all the variables analyzed, with reductions in the physiological performance of seeds submitted to the potentials -0.2 and -0.4 MPa. In relation to temperatures, seeds exposed to 20 °C had their quality reduced, whereas in the presence of higher temperatures (35 and 20-35 °C), there was greater physiological performance. However, conditioning the seeds with 40 to 50 mM of ascorbic acid minimized the damage caused by low water availability, in addition to promoting a biostimulating effect, both in adequate water condition and in the presence of a higher temperature.