Bacterial spot caused by Xanthomonas arboricola pv. pruni (Xap) is considered as a major problem in peach orchards. Copper and antibiotics are used to control, and biocontrol should be a new alternative with low environment impact. The objective was evaluated by the antibiotic activity of the metabolite produced by Pseudomonas aeruginosa LV strain. The free cells supernatant was fractionated with a serial organic solvent with crescent polarity and a dichloromethane phase was concentrated and lyophilised, and after was fractionated using vacuum liquid chromatography. The antibiotic activity of the F3 fraction containing an organometallic compound was tested on Xap in vitro and in a greenhouse conditions. Plants were sprayed with F3 before or after Xap infection and the results showed changes in exopolysaccharides and cell morphology. The F3 concentration of 450 µg•mL-1 was more effective. The results showed that F3 fraction could be a new alternative to control bacterial spot.

Huanglongbing (HLB) is the most destructive disease of citrus worldwide and an efficient management strategy to control it has not yet been established. The potential of pseudomonads to suppress plant pathogens is well known and the secondary metabolites they produce represent new alternatives of compounds to control plant diseases. The main challenge is to find new compounds that show strong antibiotic activity, low toxicity to plants and little or no harm to the environment. The objectives of the present study were to determine the potential of the F4A fraction from Pseudomonas aeruginosa to control HLB and to induce systemic resistance. Low molecular weight compounds with antimicrobial activity were purified with organic solvent, thin layer chromatography (TLC) and normal and reverse phase chromatography. Compounds present in the F4A fraction were mainly obtained by thin-layer chromatography (TLC) and Preparative-High Performance Liquid Chromatography (HPLC-prep). To assess their biological activities, conventional and quantitative polymerase chain reaction were usxed. The F4A was sprayed on citrus trees infected with the causal agent of HLB, 'Candidatus Liberibacter asiaticus' under greenhouse conditions. The bacterial titers were reduced and defense genes were induced in leaves of trees treated with F4A, as assed by PCR analysis. The results showed that F4A (pseudomonads secondary metabolites) may provide a useful tool for the management of HLB.