ABSTRACT. Synthetic pesticides have a positive impact on food production. However, there are concerns due to the outbreak of resistance along with negative side effects on human health and the environment. New active compounds and control strategies are needed for the management of phytopathogens. Antimicrobial peptides (AMPs) are evolutionarily conserved components of the innate immune response in almost all organisms that constitute an interesting source of potential molecules for use as pesticides. The naturally derived antimicrobial peptide Aq- AMP (Amaranthus quitensis-Antimicrobial Peptide), obtained from Amaranthus quitensis, is cysteine-rich with activity against several phytopathogens. In the present work, we report on the expression in Escherichia coli of functionally active Aq-AMP fused to thioredoxin (TrxAq-AMP). The in vitro antifungal activity of purified TrxAq-AMP was confirmed against Alternaria solani, Fusarium oxysporum f. sp. lycopersici, Pencillium digitatum and P. italicum, as well as the in vivo control of P. digitatum in oranges. We demonstrated the stability of TrxAq-AMP in a range of pH (from 3 to 11) and at temperatures from 0°C to 100°C. Furthermore, it maintained activity after digestion with various proteases and it displayed no haemolytic activity suggesting a highly stable and safe molecule. For topical application we present AMP with no haemolytic/phytotoxic activity that is effective, stable to a wide range of temperature and pH, and resistant to protease activity. Besides, this molecule is naturally stored in the seed, easy to extract and potentially produced through molecular farming. These findings encourage further biotechnological research on topical application of AMPs, especially in relation to molecule bioavailability.