Bioprospecção de rizobactérias com potencial de mitigação a Candidatus Liberibacter asiaticus e ao HLB

Abstract

Among the major citrus diseases currently occurring in the state of São Paulo, Brazil, Huanglongbing (HLB), caused by the bacterium Candidatus Liberibacter asiaticus (CLas), is considered the most damaging to citrus production. To date, CLas has not been successfully cultured under axenic conditions outside its hosts (plants and Diaphorina citri), which has greatly hindered research on this pathogen. Genetically related and culturable microorganisms, such as Sinorhizobium meliloti (Sme) and Liberibacter crescens, have been used as model organisms in vitro to identify antimicrobial compounds and microbial antagonists against CLas. However, efficient screening strategies require both rapid in vitro approaches and in situ methods capable of directly evaluating the behavior of potential antagonists against CLas. The objective of this study was to select and evaluate bacterial genera previously described as antagonistic to phytopathogens for their potential activity against CLas. For this purpose, we had as goals: i. Conduct in vitro antagonism assays using S. meliloti as a model organism. ii. Evaluate the selected isolates over CLas titer and the plant physiological development in infected plants under greenhouse conditions. A total of 274 bacterial isolates were screened, of which 18 exhibited inhibitory activity, belonging to the genera Bacillus, Burkholderia, Lelliottia, Methylobacterium, Serratia, and Pseudomonas. Selected isolates were subsequently evaluated in CLas-infected citrus plants. Pathogen quantification was performed by qPCR in leaves and roots, together with assessments of plant growth characteristics. The results demonstrated that several isolates significantly reduced CLas titers during the experimental period. Among them, Methylobacterium_IAC80 was the most promising, reducing bacterial populations in both leaves and roots while also promoting plant growth. The isolates Serratia_IAC568, Lelliottia_IAC75, Pseudomonas_IAC532, and Bacillus_IAC362 also showed potential to reduce CLas populations in leaves, exhibiting performance equal or superior to oxytetracycline without causing negative effects on plant development.