Considerações sobre a química de Brachiaria humidicola e efeitos alelopáticos sobre leguminosas tropicais

Abstract

Knowledge of allelopathic profile can improve the use of species of grasses and legumes with low allelopathic activity among themselves, and may thus result in a more balanced and sustainable mixed pasture. Based on these aspects, was structured this work, assuming, hypothetically, that the Brachiaria humidicola, their extracts, fractions or substances extracted from grass have allelopathic effects on tropical legumes (Stylosanthes spp., Desmodium ovalifolium, Macrotyloma axillare, Calopogonium mucunoides and Cajanus cajan). To test this hypothesis experiments were developed in the laboratory or greenhouse, to demonstrate the allelopathic effect of this grass, besides verifying, among legumes evaluated, the more tolerant. We obtained crude extracts, fractions and compounds isolated from successive and exhaustive extraction with organic solvents cold. The samples were subjected to various techniques of identifying substances such as phytochemical, using RMN 1H and 13C, GC-MS and capillary electrophoresis technique. The volatile components were obtained by hydrodistillation from fresh plant material. Despite the exploration analysis with only qualitatively characterize chemical classes or their metabolites, this technique combined with RMN 1H and 13C guided interpretation of biological events occurring in the germination bioassays. Although cinnamic acids and their derivatives have not been precisely identified in prospecting techniques and RMN, it is likely that the inhibitory effects observed are associated with them. According to the results of capillary electrophoresis low concentration of phenolic compounds were detected in the aqueous extracts of seed. While the highest concentration was found in the methanol extract of shoot. For the crude extracts of the shoot, root and seeds, legumes Stylosanthes spp. were more sensitive following C. mucunoides. M. axillare was the most tolerant. Samples of saponins obtained from the roots of B. humidicola showed high inhibitory capacity. A similar relationship was observed between the control and evaluations with flavonoids in M. axillare. The hydrolate and water decoction parts of B. humidicola (root, shoot and seed) showed inhibitory effect on the receptor species. Water decoction, mainly from the roots, resulted in a greater inhibitory effect. In contrast, the seed hydrolate showed less activity In contrast, the hidrolact seed showed less allelopathic activity. In experiments conducted in the greenhouse, the presence of straw B. humidicola the culture substrate inhibited so intense growth and dry matter production of C. Cajan and Stylosanthes spp. Readings of chlorophyll, in particular chlorophyll a/b can be used as an index of the effect of allelopathic B. humidicola on legume C. cajan. The positive response of flavonoids against germination L. sativa and M. axillare shows that the trend of improvement should prioritize studies on grasses that favor this metabolite biosynthesis.