In vitro and In vivo Antifungal Activities of Organic and Inorganic Salts Against Citrus Sour Rot Agent Geotrichum candidum

The aim of this study was to find an alternative to the chemical fungicide currently used in the control of postharvest citrus sour rot. Here we screened thirty-two salt compounds, considered as common food additives, for their activity against Geotrichum candidum, causal agent of citrus sour rot. The lowest Minimum Inhibitory Concentrations (MICs) values were obtained by ammonium carbonate and EDTA at a concentration of 0.1% (w/v) and boric acid, sodium carbonate and sodium metabisulfite at 0.25% (w/v). Over all, the medium-pH in the range of 4.0 to 12.0 did not influence the mycelial growth of the pathogen. The ten best salt compounds were tested for their ability to reduce the arthrospores germination of the fungus. The effect of salts varied significantly (p<0.05) between tested compounds and depended on their concentrations. The arthrospore germination was completely inhibited by EDTA, boric acid, sodium metabisulfite, sodium carbonate, sodium sulfate and sodium thiosulfate, both at 100 and 75 mM. The most active salts in in vitro studies were tested in vivo against sour rot on citrus fruit. Incidence of sour rot was lowered to 25.93 and 38.89%, when mandarin fruit where treated by sodium salicylate, boric acid and EDTA, compared with 100% in the control. However, only the application of boric acid at 3% (w/v) reduced disease severity by more than 70%. These results suggest that sodium salicylate, boric acid and EDTA may be useful and effective compounds for control of citrus sour rot. Such healthy products therefore represent a sustainable alternative to the use of guazatine mainly in organic production.