Análise do potencial bioherbicida de fungos selvagens cultivados em biomassa microalgal

Abstract

Weeds cause disturbances in the crop growth by presenting a rapid and unusual growth, competing for space and resources with other species, thus harming the environment, yield and quality of crops of agricultural interest. Weed control is often carried out through the use of chemical herbicides in conjunction with other conventional methods, but which end up raising concerns in the area of human and environmental health. Due to these issues, alternative methods for weed control are sought, which promote food security and the maintenance of a healthy ecosystem. In this sense, this study sought to evaluate the bioherbicidal potential of wild fungi grown in microalgae biomass from the treatment of the digestate of biogas production. For this, the microalgal biomass was separated after tertiary treatment of swine effluent and a mass of 10 g was used as a substrate for the fermentations that occurred in a submerged and solid form containing 106 spores/mL of each microorganism. The extracts from different fermentations (solid and submerged) were mixed, in the proportion of 1:1 v/v, in order to evaluate the efficiency of a mixed extract. Four fungal isolates were used: Trichoderma koningiopsis, which was isolated from the weed Digitaria ciliares, Fusarium sp. and two fungi with associated growth, Fusarium denticulatum and Mucor circinelloides, which were isolated from the intestines of military caterpillars (Spodoptera frugiperda). The extracts were evaluated for the activity of the enzymes amylase, cellulase, peroxidase, lipase and laccase. Bioherbicidal activity was evaluated through application on Cucumis sativus and leaf damage was visually estimated according to the scale recommended by the Brazilian Society of Weed Science. A preliminary characterization of the extracts was also carried out by means of a liquid-liquid extraction, in which the reaction products were identified by gas chromatography coupled with mass spectrometry. The extract with the highest phytotoxic potential was also subjected to lyophilization and drying tests in order to concentrate its enzymatic activity. The toxicity of the extracts was verified with tests on apical meristem of Allium cepa, from which the mitotic index was calculated. In a global view of the study, the microorganisms showed potential as producers of an enzymatic pool by the two fermentative methods. Among the extracts produced by solid state fermentation, those obtained by the fungi Fusarium denticulatum in consortium with Mucor circinelloides and Fusarium sp. demonstrated higher levels of leaf damage (80-100 ± 3.00%). In submerged fermentation, with the fungi Trichoderma koningiopsis and Fusarium sp., irreversible leaf damage was obtained in the tested cultures. The combined extract from the submerged fermentation of the fungus Fusarium sp. and by the solid fermentation of the Fusarium denticulatum and Mucor circinelloides fungi consortium, it presented a severe phytotoxic effect (98.00 ± 3.00%), which demonstrates the synergistic action on the target plant, probably because the enzyme pool present in this extract is composed of amylase, cellulase, lipase and peroxidase. The profile of compounds present in the extracts is basically organic compounds, but their contributions to the bioherbicidal action are not yet known. For all analyzed enzymes, the lyophilization technique was the most efficient in the concentration process. As for toxicity, the results showed positive effects, with low potential for contamination. Through the tests carried out, it can be inferred that the microbial strains are potential agents of biological control of invasive plants, which together with the biomass of microalgae, offered the appropriate conditions to obtain an enzymatic pool of biotechnological relevance and with promising characteristics to be explored as a bioherbicide, addressing aspects of environmental sustainability.