Avaliação de Pseudoallinostoc soli como bioinsumo na nutrição de feijoeiro

Abstract

Cyanobacteria are prokaryotic, autotrophic, and highly adaptable microorganisms with considerable morphological and metabolic diversity. Their ability to fix atmospheric nitrogen, particularly among members of the order Nostocales due to the presence of heterocytes, enables their survival under adverse environmental conditions and makes them promising candidates for biotechnological applications in agricultural systems. In addition, cyanobacteria produce bioactive compounds such as exopolysaccharides (EPS), antioxidants, and enzymes, which have been explored for promoting plant growth and improving soil quality. In this context, the use of cyanobacterial biomass as a biofertilizer and biostimulant has emerged as a sustainable alternative, contributing to a reduced dependence on chemical fertilizers. The objectives of this study were to perform a comparative physiological characterization of five cyanobacterial strains belonging to the order Nostocales in order to select the strain with the greatest biotechnological potential and subsequently evaluate the biofertilizer effect of the selected strain on the cultivation of Ouro Negro black bean (Honduras 35). In the first stage, biomass growth (absorbance and dry weight), chlorophyll a concentration, EPS production, and nitrogenase activity were evaluated. In the second stage, under greenhouse conditions, the biomass of the selected strain was cultivated in BG110 medium under controlled conditions and applied to bean plants every seven days after the emergence of the first trifoliate leaf. The experiment was conducted in a completely randomized design with three treatments (NF, F, and N) and eight replicates. Biometric parameters, leaf pigments, yield, and soil microbiological attributes were evaluated. The UFLA 37 strain exhibited the highest chlorophyll a concentration (3.88 µg mL⁻¹) and mean absorbance (A680 = 3.54), indicating greater photosynthetic efficiency and superior growth compared with the other strains. It also showed high nitrogenase activity (94.84 ± 76.16 nmol N₂ g⁻¹ DW h⁻¹) and consistent EPS production (10 mg from 220 mg of biomass), being selected based on the overall physiological parameters evaluated. Agronomic assessment demonstrated that biomass application, particularly when combined with commercial fertilizer, promoted greater vegetative growth of bean plants, reflected by increases in plant height (14.44 cm), stem diameter (4.25 cm), number of leaves (6.25), and root length (38.33 ± 19.14 cm), as well as a higher soil microbial population (9.80 × 10⁵ CFU). Regarding yield, the combination of biomass and commercial fertilizer favored pod formation (11.80), whereas commercial fertilizer applied alone contributed more efficiently to grain filling (15.31 g), indicating a complementary effect between treatments. These results demonstrate that selection based on physiological characterization is an efficient strategy for identifying strains with promising potential as biofertilizers. Furthermore, the application of biomass from the selected strain shows potential for use as a biofertilizer in agricultural systems, particularly when integrated with mineral fertilization, contributing to plant growth, productivity, and soil biological quality, thereby reinforcing its application as a biotechnological tool for sustainable agriculture.