Comparative study of antimicrobial peptides to control citrus postharvest decay caused by Penicillium digitatum

The objective of this study was to investigate and compare the in vitro efficacy and in vivo potential of eight distinct short antimicrobial peptides to control the postharvest green mold disease of oranges caused by the fungus Penicillium digitatum. The L-amino acid versions of the four peptides PAF26, PAF38, PAF40, and BM0, previously obtained by combinatorial approaches, were examined. The study included two antibacterial peptides formerly identified by rational design, BP15 and BP76, and it is demonstrated that they also have in vitro antifungal properties. The natural antimicrobial peptides melittin and indolicidin were also selected for comparison, due to their well-known properties and modes of action. In vitro and in vivo results indicated differential behaviors among peptides, regarding the inhibitory potency in growth media, selectivity against distinct microorganisms, fungicidal activity towards nongerminated conidia of P. digitatum, and efficacy in fruit inoculation assays. Interestingly, a high in vitro inhibitory activity did not necessarily associate with an effective control of fruit infection by P. digitatum. The short tryptophan-rich cationic peptides PAF26, PAF38, PAF40, and BM0 were lethal to conidia of P. digitatum, and this property is correlated with better protection in the decay control test.