Caracterização de rizobactérias no porta-enxerto citrumelo ‘swingle’ sob sistemas de cultivos orgânico e convencional

Abstract

Understanding the impact of the plant microbiome has driven new strategies to enhance agricultural production, especially in the face of climate change, increased prevalence of pathogens, and adverse growing conditions. Studying soil microorganisms is essential for transforming the rhizosphere to benefit plants, but there is still a knowledge gap regarding the prospecting of Plant Growth-Promoting Bacteria (PGPB) in citrus, particularly when comparing different cultivation systems. This project investigated citrus rhizobacteria under organic and conventional cultivation systems, aiming to identify microorganisms with potential for the formulation of synthetic communities (SynComs) and their application as bioinputs. Rhizospheric soil samples were collected for total soil DNA sequencing to perform metataxonomic analyses, and root samples were collected to isolate bacterial populations from the rhizosphere and rhizoplane using four culture media to maximize bacterial diversity. After morphological selection, the isolates were cryopreserved and taxonomically characterized by sequencing the V4-V5 region of the 16S rRNA gene using the Illumina platform (250x250bp paired-end), allowing identification at the genus level. Through in silico analyses, a core community of approximately 76% was observed across both cultivation systems, along with higher alpha diversity and a greater number of biomarkers in organic cultivation. Beta diversity indicated that the cultivation type explained 25% of the variation in microbial community composition. In vitro assays were conducted to functionally characterize the isolates, including phosphate solubilization, indole-3-acetic acid (IAA) production, siderophore production, and nitrogen fixation tests. In vivo assays were also carried out, including seed germination tests and seed inoculation in seedling trays under greenhouse conditions to assess the potential of the bacteria as PGPB. A total of 61 isolates were tested in vitro, with up to 70% of isolates from organically grown plants exhibiting phosphate solubilization ability and approximately 80% demonstrating siderophore production potential. In contrast, isolates from conventional cultivation stood out for their biological nitrogen fixation capacity, with 55% showing this trait. In the seed germination tests, isolates from the organic system significantly accelerated germination speed and vigor, while the SynCom formed from conventionally derived bacteria—selected based on their growth-promotion abilities—showed a significant positive effect (p<0.05) on root mass (g). In the in vivo assays, 16 isolates significantly increased (p<0.05) root volume in plants. The results of this study reinforce the potential of the isolated bacteria, particularly from organic cultivation, in promoting plant growth and developing sustainable strategies for citrus farming. Furthermore, the formation of SynComs represents an innovative approach for the formulation of bioinputs, contributing to plant resilience under different cultivation conditions.