Síntese de vidros polifosfato e borofosfato à baixa temperatura para aplicação como agentes antifúngicos

Abstract

Fungal diseases represent one of the major threats to global agricultural production, causing significant losses in crop productivity and quality. To mitigate these impacts, chemical fungicides have been the most widely applied strategy. However, the increasing resistance of phytopathogens to these compounds reduces their effectiveness over time, requiring the search for more sustainable and effective control alternatives. This study investigated the synthesis of polyphosphate and borophosphate glasses at low temperatures, aiming at their application as antifungal agents for controlling phytopathogenic fungi. Polyphosphate glasses were prepared by combining potassium dihydrogen phosphate and ammonium dihydrogen phosphate in a molar ratio of 1, while borophosphate glasses were synthesized by adding boric acid to the same polyphosphate ratio using the melt-quenching method. To enhance the antifungal efficacy of the glasses, a full fractional experimental design was employed with three (3) factors: melting temperature (300–400 °C), melting time (1–2 h), and boric acid content (0–2%), aiming to identify the conditions that yield the highest antifungal activity. The synthesized glasses were characterized using Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, moisture absorption analysis, and density determination. Microbiological assays included agar well diffusion tests, determination of minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC), and evaluation of radial mycelial growth inhibition for the fungi Macrophomina phaseolina, Sclerotinia sclerotiorum, and Botrytis cinerea. Additionally, structural damage to hyphae was analyzed by optical microscopy after treatment with the glasses. The glasses were also applied in the treatment of strawberries to evaluate their efficacy in extending shelf life under storage conditions. FTIR and Raman spectroscopy characterization revealed characteristic bands of polyphosphate and borophosphate, with predominant symmetric and asymmetric P–O–P and O–P–O vibrations in Q² species for both matrices. Structural modifications were observed, attributed to variations in temperature, reaction time, and the addition of boric acid, directly impacting the hygroscopicity and density of the glasses. Under synthesis conditions of 400 °C for 1 h, both polyphosphate and borophosphate glasses exhibited superior antifungal activity against the tested strains. In the agar well diffusion test, borophosphate glasses showed the largest inhibition halo against Macrophomina phaseolina, with a diameter of up to 47.98 mm. MIC and MFC values were similar for both matrices, with MIC ranging from 1.95 to 3.90 mg/mL, MFC at 125 mg/mL, and inhibition percentages reaching up to 88.10%. Microscopic analysis revealed structural alterations in hyphae, and the application on strawberries effectively controlled B. cinerea without compromising fruit quality, highlighting the potential of these materials in controlling phytopathogenic fungi.