Exploring the rhizospheric microbiota of Citrumelo Swingle rootstock in the field under water stress conditions

Abstract

The microbial community in the rhizosphere differs from the soil microbiota because it is influenced by root exudates and soil physicochemical properties. This enables the development of distinct beneficial microorganisms for plants. Among the benefits of this microbiota, the ability to provide nutrients through nitrogen fixation, phosphorus solubilization, and siderophore production stands out. Also noteworthy is the capacity to induce systemic resistance to both biotic and abiotic stress. Additionally, they can trigger morphological, physiological, and biochemical changes that enhance a plant's tolerance to water deficit. Due to the importance of the rhizospheric microbiota and the underexplored potential of these microorganisms for citrus cultivation, this study hypothesizes that the presence of plant growth-promoting bacteria (PGPB) is associated with phenotypes of reduced water stress damage in citrus plants. The main objective is to compare the populations of rhizobacteria in sweet orange plants with differential levels of water stress at different times of the year, and to select, through sequencing and physiological characterization, specimens with potential benefits for plants. Root samples from the Valencia variety grafted onto Citrumelo Swingle rootstock, exhibiting contrasting water deficiency symptoms, were collected in the Northwestern region of the State of São Paulo, in the municipality of Onda Verde. The isolates are being sequenced for the 16S rRNA gene and will be categorized at the genus level through bioinformatics analyses. Species and genera previously described as potential PGPBs found in the collection will be characterized in vitro for their potential to solubilize phosphorus, produce siderophores, produce auxin, and for mechanisms involved in water stress mitigation, such as the production of aminocyclopropane-1-carboxylate (ACC) deaminase, exopolysaccharide production, and biofilm formation. Isolates exhibiting growth-promoting characteristics will be selected to form a synthetic community (SynCom) for testing in vivo experiments on citrus plants under greenhouse conditions. It is expected that the constructed SynCom will contribute to the development of a bio-stimulant for use during citrus seedling formation.