Abstract: Sour rot, caused by Geotrichum citri-aurantii, is one of the most devastating diseases of harvested citrus fruit. Nonetheless, there are currently no efficient fungicides available to control this disease. In this study, ammonium carbonate as a generally recognized as safe compound was evaluated for its antifungal activity against the pathogen and the possible mechanism of its action was investigated. The results showed that ammonium carbonate could inhibit spore germination, germ tube elongation and mycelial growth of G. citri-aurantii in vitro in a dose-dependent manner, completely inhibiting spore germination and mycelial growth at a concentration of 0.8 g/L. Further analysis revealed that ammonium carbonate inhibited spore activity, powerfully repressed mycelial respiration, altered the permeability of cell membrane as indicated by propidium iodide (PI) staining, and gradually increased the leakage of intracellular ions, proteins and nucleic acids, thus leading to the functional loss of hyphal cells. In vivo experiment demonstrated that 20 g/L ammonium carbonate could effectively decrease lesion diameter in Valencia oranges artificially inoculated with a spore suspension at 1 × 106 spores/mL, 20 μL and reduce disease incidence. These results suggested that ammonia carbonate could be a potential alternative to fungicides to control sour rot in citrus fruit.

Key words: ammonium carbonate; Geotrichum citri-aurantii; inhibition; action mechanism; citrus fruit