Does sorghum phenolic extract have antifungal effect?

Abstract

This study aimed to evaluate the antifungal effect of SC319 sorghum phenolic extract (SPE) on the Aspergillus, Fusarium, Penicillium, Stenocarpella, Colletotrichum, and Macrophomina genera. SPE was extracted by 20% ethanol and used in four assays: (1) against Fusarium verticillioides in solid (PDA) and liquid (PD) potato dextrose media; (2) Minimum Inhibitory Concentration (MIC) assay with 16 fungi isolates; (3) Conidial Germination Rate (CGR) with 14 fungi isolates and (4) Growth Curve (GC) with 11 fungi isolates. There was no reduction in the mycelial growth (colony diameter and dry weight) and in the number of Fusarium verticillioides spores in assay 1 (PDA and PD). The colony's dry weight was almost six times higher in the presence than in the absence of SPE. All SPE samples presented MIC (assay 1) above the maximum concentration tested (5000 µg.mL^-1) for the 16 isolates. Also, there was no inhibitory effect of SPE on conidia germination rate (CGR). Oppositely, in GC assay, the control had a higher CFU count than the samples with SPE in 24 h. This result suggests that SPE can delay the fungal growth in the first hours of incubation, which is an important finding that may help reduce the severity of fungal diseases in plants. However, further studies are needed to confirm these results, including sorghum genotypes with different profiles of phenolic compounds. Although the SC319 SPE was not effective as an antifungal agent, it may have potential as a growth promoter of beneficial fungi in the food and pharmaceutical industries.

Keywords: Sorghum bicolor (L.) Moench; Biofungicide; Minimum inhibitory concentration; Toxigenic fungi.

Fig. 1

Summary of assays performed to evaluate the antifungal effect of phenolic sorghum extract

Fig. 2

Effect of sorghum phenolic extract (SPE) on conidia germination rate (CGR). Percentage of germinated conidia for fungal species (A—N) after 24 h in PD medium in the absence (control) and in the presence of SPE (5000 µg.mL.⁻¹). * Significant difference (p < 0.05) in relation to the absence of SPE **(p < 0.01); *** (p < 0.001)

Fig. 3

Effect of sorghum phenolic extract (SPE) on the growth curve (GC) of fungal species. Total colony-forming unit (CFU.mL⁻¹) of the fungal species (A—K) at 0, 8 and 24 h in the absence (control) and presence of SPE (5000 µg.mL.⁻¹). Significant difference in relation to the absence of the SPE *(p < 0.05); **(p < 0.01); ***(p < 0.001)