Aim: To evaluate the activity against fungal phytopathogens of two synthetic peptides derived from the protein bovine lactoferricin: the antibacterial active core of six amino acid residues (LfcinB₂₀₂₅) and an extension of 15 amino acids (LfcinB₁₇₃₁).

Methods and Results: In vitro activity against fungal pathogens was determined and compared with that against model micro-organisms. Activity was demonstrated against fungi of agronomic relevance. Distinct antimicrobial properties in vitro were found for the two peptides. LfcinB₁₇₃₁ had growth inhibitory activity higher than LfcinB₂₀₂₅. However, LfcinB₁₇₃₁ was not fungicidal to quiescent conidia of Penicillium digitatum at the concentrations assayed, while LfcinB₂₀₂₅ killed conidia more efficiently. Microscopical observations showed that the mycelium of P. digitatum treated with LfcinB₁₇₃₁ developed alterations of growth, sporulation and chitin deposition, and permeation of hyphal cells. In experimental inoculations of mandarins, both peptides showed limited protective effect against the disease caused by P. digitatum.

Conclusions: LfcinB₂₀₂₅ and LfcinB₁₇₃₁ peptides were shown to have antimicrobial activity against plant pathogenic filamentous fungi, with distinct properties and mode of action.

Significance and Impact of the Study: LfcinB₂₀₂₅ and LfcinB₁₇₃₁ peptides offer novel alternatives to develop resistant plants by molecular breeding.