Produção de ácido giberélico em diferentes condições de fermentação e avaliação da aplicação agronômica do sobrenadante de cultivo

Abstract

Gibberellic acid (GA3) is a plant hormone belonging to the gibberellin group, which functions to enhance various growth and development factors in plants, such as seed germination, flowering, vigor, root growth, stem elongation, and consequently nutrient absorption. This acid can be produced by different methods; however, the most studied are solid-state fermentation and submerged fermentation. Given the relevance and biotechnological application opportunities in agriculture, this study aims to evaluate different strains of Fusarium fujikuroi and Aspergillus niger as potential GA3 producers, as well as to define the optimal fermentation conditions and the use of additives in the culture medium. Preliminary assays for selecting the strains with the highest acid production potential indicated the microorganisms Insumicro 175 and LGB-034-2015, which achieved yields of 8.11 mg gibberellic acid/g substrate and 6.57 mg gibberellic acid/g substrate, respectively. To evaluate the fermentation conditions, a 2³ factorial design was performed with the variables: fungus, temperature, and initial pH. The results showed that, regardless of the fungus, the best fermentation conditions were at a temperature of 28ºC and pH 5.0. The fungi LGB-034-2015 and Insumicro 175 achieved good production yields, with a maximum of 13.66 mg gibberellic acid/g substrate and 9.18 mg gibberellic acid/g substrate, with the Aspergillus genus strain being superior. Evaluating the effect of adding glycerol or yeast extract at previously determined concentrations, there was a reduction in production yield for both microorganisms; however, an increase in substrate consumption speed was observed. Subsequently, a central composite design was carried out to find the best substrate composition for maximum GA3 production. Thus, it was determined that for optimal conditions, the substrate composition should contain 26.4 g/L glucose, 8.7 g/L yeast extract, and 2.1 g/L glycerol for Fusarium fujikuroi, and for Aspergillus niger, the glycerol value should be increased to 4 g/L. In this composition, the gibberellic acid concentration is 580 ppm. To verify the supernatant's potential in relation to soybean seed germination, an increase in the number of normal soybean seedlings was observed by about 30% and a reduction in the number of abnormal plants by around 40% with a dose of 100 mL/100 kg of seeds. For evaluating the growth promotion of soybean plants, the supernatant showed improvements in all observed parameters, namely: aerial green mass (15%) and roots (31%), aerial dry mass (56%) and roots (56%), and root volume (18%), also indicating an 10 optimal dose close to 100 mL/100 kg of seeds. Regarding the agronomic effect observed in the bean crop, the supernatant at a dose of 2000 mL/ha promoted an increase of 5 sc/ha and significantly differed from the control treatment. Additionally, the supernatant has the capacity to reduce plant stress effects; however, not through enzymatic mechanisms. Therefore, future studies should be developed to understand the supernatant's mode of action, as well as applications in other economically important crops in Brazil.