Antimicrobial Peptides for Plant Disease Control. From Discovery to Application

Sustainable protection of plant crops against diseases relies on a rational use of pesticides and to a reduction of the number of active ingredients to the more selective, less toxic and with a lower negative environmental impact. Antimicrobial peptides (AMPs) are envisaged as new plant disease control products because of the need for novel antifungals, antibacterials and plant strengtheners in Agriculture. Natural AMPs are produced in low amounts, some are toxic, or low active or unstable, and require generally complex and costly procedures for extraction and purification from the producing organism. Synthetic AMPs offer alternatives but require pharma approaches for development as plant protection products. We have developed linear undecapeptides (CECMEL11) and cyclic decapeptides (CYC10) against plant pathogens following the classical hit-to-lead and lead optimization approaches, based on combinatorial chemistry of some critical positions in their amino acid sequence. The peptides were improved for activity against plant pathogenic bacteria and fungi, but minimizing hemolytic activity and protease susceptibility. The selected peptides covered a wide range of action spectrum. Peptide BP100 was strongly lytic against Gram negative bacteria including plant pathogenic bacteria and food-borne human bacterial pathogens, but poorly antifungal. Peptide BP21 displayed strong fungicidal and sporicidal activity but slight antibacterial activity. Acute oral toxicity in mice is slight or non-toxic. Proof-of-concept assays have been performed with success including whole plant tests against Erwinia amylovora and Pseudomonas syringae on pear, and Xanthomonas axonopodis pv. vesicatoria on pepper, as well as in postharvest against Penicillium -rot on apple. The main limitation of the implementation of the antimicrobial peptide technology in the field of plant protection is due to the production costs, but strong efforts are in progress to produce these peptides using microbial and plant biofactories.