Abstract: Phloem-restricted Candidatus Liberibacter species are the causative agents of economically significant crop diseases, including citrus Huanglongbing (HLB) and potato zebra chip disease (ZCD). ZCD, caused by Candidatus Liberibacter solanacearum (CLso), and transmitted by the potato psyllid, has spread to over 56% of United States potato production areas, resulting in millions of dollars in annual losses. Current control strategies rely on eliminating infected plants and reducing vector populations using insecticides, which have limited efficacy, pose risks to human and animal health, and raise environmental concerns and drug-resistant insect vectors. We have previously identified a novel stable antimicrobial peptide (SAMP) from Australian finger lime that can inhibit citrus HLB by suppressing C. Liberibacter asiaticus (CLas) growth and activating plant immune responses. In this study, we evaluated SAMP for controlling the CLso pathogen in solanaceous crops, as well as an unrelated vascular pathogen (Xanthomonas campestris pv. Campestris (Xcc)) in Arabidopsis thaliana. Topical application of SAMP on potato and tomato plants increased resistance to CLso in greenhouse trials. Potatoes and Arabidopsis internally expressing SAMP by the transgenic approach showed no growth defects and had significantly reduced bacterial titers after pathogen challenge. Remarkably, SAMP also suppressed CLso within the insect vector. These results highlight the broad-spectrum efficacy of SAMP, demonstrating its potential for bioengineering disease-resistant plants as a sustainable, cross-crop tool to combat vascular bacterial pathogens and enhance plant immunity beyond citrus species.

Key words: antimicrobial peptides, Bactericera cockerelli, Candidatus Liberibacter, plant defense priming, Xanthomonas campestris pv. campestris, zebra chip disease