Control of green and blue mold and sour rot in citrus fruits by the cationic antimicrobial peptide PAF56

The ability of the short cationic antimicrobial peptide PAF56 (amino acid sequence GHRKKWFW) to control postharvest infectious diseases of citrus fruits was evaluated. PAF56 inhibited the growth of Penicillium digitatum, Penicillium italicum and Geotrichum candidum. The minimum inhibitory concentrations (MICs) of PAF56 for the control of P. digitatum, P. italicum and G. candidum were 8, 16, and 8 μM, respectively. The conidia of P. digitatum, P. italicum and G. candidum were also highly sensitive to PAF56. The peptide PAF56 could effectively control green mold, blue mold and sour rot on inoculated citrus fruits. Fluorescence microscopy with the fluorescent stains SYTOX Green (SG) and Calcofluor White (CFW) was used to characterize the modes of action and interaction of PAF56 with the mycelia of P. digitatum, P. italicum and G. candidum. SG and CFW signals indicated that PAF56 could inhibit the formation of spores and change the cell membrane permeability and cell wall structure. A range of concentrations of PAF56 (from 16 to 128 μM) showed no hemolysis or toxicity to human red blood cells (erythrocytes).