Selection of Small Synthetic Antimicrobial Peptides Inhibiting Xanthomonas citri subsp citri Causing Citrus Canker

Citrus canker disease decreases the fruit quality and yield significantly, furthermore, emerging of strep-tomycin--resistant pathogens threatens the citrus industry seriously because of a lack of proper control agents. Small synthetic antimicrobial peptides (AMPs) could be a promising alternative. Fourteen hexapeptides were selected by using positional scanning of synthetic peptide combinatorial libraries. Each hexapeptide showed different antimicrobial spectrum against Bacillus, Pseudomonas, Xanthomonas, and Candida species. Intriguingly, BHCIO showed bactericidal activity exclusively on Xanthomonas citri subsp. citri (Xcc), while BHC7 was none-active exclusively against two Pseudomonas spp. at concentration of 100 pg/ml suggesting potential selectivity constrained in hexapeptide frame. Three hexapeptides, BHCO2, 06 and 11, showed bactericidal activities against various Xcc strains at concentration of 10 mu g/ml. When they were co-infiltrated with pathogens into citrus leaves the disease progress was suppressed significantly. Further study would be needed to confirm the actual disease control capacity of the selected hexapeptides.