Padronização dos métodos de análises da cercosporina e isocercosporina do extrato de Cercospora brachiata e avaliação da atividade herbicida e de danos à biomembranas de lipossomas

Abstract

The fungus Cercospora brachiata was reported in Brazil for the first time in 2019 as Caruru leaf spot, and as it belongs to the genus Cercospora, it is known to be responsible for diseases in several plant species, causing great economic losses. However, phytopathogenicity can be used to develop new herbicides or bioherbicides. This research, therefore, aimed to evaluate the herbicidal activity of the ethyl acetate extract of this fungus, as well as its phytotoxin cercosporin, against the plant species Amaranthus viridis (Caruru). This work also reported for the first time the production of the phytotoxin cercosporin and its main isomer isocercosporin, in the species C. brachiata, as not all species of this genus are capable of producing this substance. Furthermore, it was possible to characterize the substances by NMR (Nuclear Magnetic Resonance), quantification by HPLC (High Performance Liquid Chromatography) and assessment of damage caused by cercosporin to lecithin liposome biomembranes, before and after exposure to substance to light. During the study, it was found that the fungus produces phytotoxins (cercosporin and isocercosporin) only when its growth occurs in the presence of light. Quantification by HPLC showed that the cercosporin content is equivalent to 20% of the extract, while the amount of isocercosporin is equivalent to 0.36% of the extract. In the evaluation of herbicidal activity, cercosporin did not show activity against Caruru at the concentration evaluated, but the extract showed activity at a concentration of 5.0 mg mL-1. The analysis of damage to the liposome biomembrane was carried out using the PTS/MV system (sodium pyrene tetrasulfonate/methyl violagen) allowing to verify that non-irradiated and irradiated cercosporin can promote damage to liposome biomembranes, but that the speed of damage is very higher in the presence of irradiation. Other studies must be carried out to understand the interactions between the substance under study and the cell membrane layer systems and evaluate other components that may interfere with the herbicidal activity of the fungus studied.