HEBERT Elvira Maria
congresos y reuniones científicas
Antagonist activity of lactic acid bacteria against fungal postharvest pathogens of citrus.
Congreso; LVII SAIB Meeting - XVI SAMIGE Meeting SAIB - SAMIGE Joint Meeting online; 2021
Postharvest diseases caused mainly by green mold (Penicillium digitatum) and blue mold (P. italicum) led to economic losses in the Argentine citrus production, by affecting the shelf-life and quality of fresh fruits. Several synthetic fungicides are commonly used to control the fungal phytopathogens. Their widespread use has led to the appearance of resistant isolates; thus, there is an urgent need to develop natural and safe strategies to control postharvest diseases and to guarantee fruit conservation through alternative technologies. Biocontrol has received much attention in the last years. Lactic acid bacteria (LAB) are the most promising candidates to be used as fungal antagonists, since they have been reported to have strong antimicrobial properties and are considered harmless to human health. The aim of this study was to evaluate the potential antifungal activity of several LAB strains against P. digitatum and P. italicum, and to determine the nature of the antifungal metabolites produced. First, inhibitory activities of Lactobacillus fermentum CRL 973, L. paraplantarum CRL 1905, L. casei CRL 1110 and L. plantarum Q1 strains were assayed by the overlayed method as a fast preliminary screening. Based on the inhibition halo, all strains showed an antifungal ability against both fungi, exerting a major activity against P. italicum. Next, LAB were grown in MRS medium at 37 °C; at 24 and 48 h, cells were removed, and cell-free supernatants (CFS24 and CFS48, respectively) were obtained by filtration. The antifungal activity of each CFS was evaluated in a 96-well polystyrene microtiter plate containing the conidial suspensions adjust to 105 CFU/ml. Microplates were incubated during 5 d at 22°C, and conidia germination was evaluated by observation using an inverted light microscope. Additionally, conidia viability after each time incubation was determined. Results showed that CFS24 and CFS48 from CRL 1905 and Q1 strains, and CFS24 from CRL 973 inhibited conidia germination of P. digitatum until 5 d of incubation, while CFS of most strains delayed P. italicum germination. It is worth to mention that the CFS inhibitory activity seems to be fungistatic, since conidia viability was maintained after treatments. To determine the nature of the antifungal compound, the different CFS were submitted to heat, proteinases treatment or neutralization. It was observed that most CFS lost their antagonistic properties after pH neutralization, suggesting an acidic nature of the antifungal metabolite. In vivo assays on lemons are necessary to detect whether CFS has a potential application for the prevention and control of postharvest diseases. Our results showed that LAB could be a promising alternative to be used as natural preservatives in postharvest lemons to control fungal growth.