Caracterização bioquímica e funcional de isolados bacterianos com potencial de promoção de crescimento e biocontrole em arroz

Abstract

Rice (Oryza sativa L.) plays a crucial role in global food supply and is cultivated under two main production systems: upland rice and irrigated rice. Upland rice is grown under nonflooded conditions, relying primarily on rainfall for its development. However, the productivity of this system faces challenges due to the occurrence of diseases such as rice blast, brown spot, and sheath blight, as well as periods of drought. In this context, this study highlights the importance of plant growth-promoting rhizobacteria (PGPR) in mitigating biotic stresses, such as diseases, and abiotic stresses, such as water deficit, as well as in promoting rice growth. The objective of this study was to biochemically and functionally characterize the potential of 13 bacterial isolates from the Embrapa Rice and Beans collection in promoting rice plant growth and suppressing major diseases affecting the crop under controlled laboratory and greenhouse conditions. The specific objectives were to compare the efficiency of the isolates in producing acid and alkaline phosphatases; solubilizing phosphorus (P), potassium (K), and zinc (Zn); producing extracellular enzymes such as amylase, cellulase, and lipase; producing indole-3-acetic acid (IAA), biofilm, and biological nitrogen fixation; evaluating the efficiency of extracted biofilm in promoting plant growth; assessing the antagonistic activity of the isolates against Pyricularia oryzae, Bipolaris oryzae, and Rhizoctonia solani; determining compatibility among selected isolates; and detecting morphological changes induced in the root system by the bacteria and their derivatives. The results demonstrated the ability of different isolates to solubilize phosphorus, zinc, and potassium, as well as to produce enzymes, biofilm, and exopolysaccharides (EPS), traits that contribute to improved plant nutritional efficiency and adaptation to adverse conditions. Antagonism assays indicated that isolates BRM69515 and BRM69524 exhibited strong activity against phytopathogenic fungi, reinforcing their applicability as biocontrol agents. In in vitro assays with rice seedlings, isolate BRM69524, either alone or combined with EPS, stood out in promoting shoot and root growth, while BRM69521 showed remarkable performance in inducing very fine roots. EPS also significantly contributed to plant development across all evaluated parameters. Overall, these findings highlight the multifunctional nature of the studied bacterial isolates and reinforce their potential as promising bioinoculants to reduce dependence on chemical inputs and promote more sustainable agricultural systems.