ORIGINAL ARTICLE Low-molecular-weight metabolites produced by Pseudomonas aeruginosa as an alternative to control Huanglongbing in Citrus sinensis cv. Valencia Juliana F. Pistori 1,2 & Ane S. Simionato 1 & Miguel O. P. Navarro 1 & Matheus F. L. Andreata 1 & Igor M. O. Santos 1 & Luciana Meneguim 2 & Rui P. Leite Junior 2 & Admilton G. Oliveira 1 & Galdino Andrade 1 Received: 21 March 2017 /Accepted: 25 May 2018 # Sociedade Brasileira de Fitopatologia 2018 Abstract 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 metab- olites 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. Keywords Natural products . Systemic acquired resistance (SAR) . Citrus . Secondary metabolites Introduction Huanglongbing (HLB), also known as Greening, is consid- ered the most destructive disease of citrus production in the world (Bové 2006). HLB is caused by three non-cultured Gram-negative bacterial species of the provisional genus ‘Candidatus Liberibacter ’, which are transmitted mostly by phloem-feeding insects, such as Diaphorina citri and Trioza erytreae (Bové 2006). HLB causes intense defolia- tion, fruit abscission, and reduces the number of production years of infected orange trees (Gottwald et al. 2012). Furthermore, there are not effective control measures for HLB. Nowadays, the management of the disease involves the use of healthy nursery cuttings for planting, eradication of diseased trees from contaminated areas, and frequent in- secticide sprays for vector control (Bové 2006; Belasque et al. 2009; Belasque et al. 2010). Application of several chemicals, such as antibiotics (Bové 2006 ) and different fertilizer formulations (Gottwald et al. 2012; Bassanezi et al. 2013), has been tested to control HLB with little success. One of the most promising strategies to control plant diseases is the use of natural compounds to induce a systemic response in the plant against the pathogen, the so-called systemic acquired resistance (SAR) (Louws et al. 2001). Elicitor Section Editor: Alessandra A. de Souza Electronic supplementary material The online version of this article (https://doi.org/10.1007/s40858-018-0231-3) contains supplementary material, which is available to authorized users. * Galdino Andrade gal.andrade7@gmail.com 1 CCB, Department of Microbiology, Microbial Ecology Laboratory, Universidade Estadual de Londrina, Londrina, PR 86051-990, Brazil 2 Bacteriology Laboratory, Instituto Agronômico do Paraná, Londrina, PR 86105-000, Brazil Tropical Plant Pathology https://doi.org/10.1007/s40858-018-0231-3