Rizobactérias e silício no manejo da cultura do arroz de terras altas ao déficit hídrico e à brusone

Abstract

Rice (Oryza sativa L.) is one of the cereals with the highest potential for providing and maintaining human nutritional needs. Biotic factors (Magnaporthe oryzae) and abiotic factors (water deficiency) can compromise rice crops, such as diseases that reduce productivity and affect grain quality, as well as conditions of water stress. Additionally, the limited availability of Phosphorus (P) in the Cerrado soil stimulates the search for technologies such as phosphorus-solubilizing rhizobacteria and plant growth promoters to improve the acquisition of scarce minerals by plants and mitigate these stresses. The present study aimed to evaluate the combination of plant growth-promoting rhizobacteria (Serratia marcescens and Bacillus toyonensis) and silicon (Si) in managing upland rice crops under water deficit and blast stress. In the first study, S. marcescens showed potential to solubilize non-labile phosphorus and promote plant growth. Inoculation with S. marcescens increased root area by 61.5%, volume by 31.5%, and length by 101%. The presence of phosphorus solubilization halos around root segments confirmed its solubilizing action. Scanning electron microscopy (SEM) detected biofilms and microcolonies of the bacteria. Genome analysis revealed genes related to indole-3-acetic acid biosynthesis, phosphate solubilization, and biofilm production. In the second study, the combination of S. marcescens and B. toyonensis with silicon and non-labile phosphorus was tested under different osmotic pressures to evaluate resistance to water stress. The combination increased surface area: 27.5% (0 MPa), 20% (-2 MPa), and 18.5% (-4 MPa); root volume: 150% (0 MPa), 58% (-2 MPa), and 55% (-4 MPa); total length: 67.5% (0 MPa) and 116.5% (-2 MPa); thick roots: 158.5% (-2 MPa) and 25.5% (-4 MPa); very fine roots: 18.5% (-2 MPa) and 30% (-4 MPa). The presence of halos around microbiolized plant segments confirmed phosphorus solubilization. SEM revealed biofilms, microcolonies, and glycocalyx under different osmotic conditions. In the third study, rhizobacteria combined with Si suppressed blast and mitigated the effects of drought in rice grown in a greenhouse. Key results include: rice productivity increased by 72% under water deficit and 35% under irrigation; reduction of panicle blast (PBS) by 60% under water deficit and 77% under irrigation; reduction of blast on the auricle and ligule by 44% under water deficit and 70% under irrigation; positive modulation of antioxidant enzymes and defense-related proteins. In the fourth study, the impact of bioagents and silicon on suppressing blast and promoting rice growth under low phosphorus availability was analyzed in two field crops. Bioagents and silicon reduced leaf blast (LBS) by 77.93% and panicle blast (PBS) by 62.37%. Additionally: the Area Under the Disease Progress Curve (AUDPC) was reduced by 77.3% (LBS) and 60.6% (PBS); grain yield in the first crop (E1) was 25% higher than in the second crop (E2). In E2, productivity increased by 71.95% (2435.72 kg/ha) compared to the control. The combination of bioagents and silicon improved biochemical and enzymatic indicators, reducing the impact of blast and optimizing rice productivity in low soil fertility conditions. In the fifth study, the interaction between rhizobacteria and silicon promoted growth, nutrient absorption, and rice productivity under low phosphorus availability. The results were: suppression of blast, reduction by 77.93% (LBS) and 62.37% (PBS); reduction of AUDPC: 77.3% (LBS) and 60.6% (PBS); increased nutrient absorption: phosphorus (45%); potassium (21%); iron (94%); manganese (50%); zinc (10%). Improvement in plant growth: height increased by 10%; number of tillers by 19%; number of panicles by 43%; aerial biomass increased by 49%; reduction of panicle sterility by 49%; productivity increased by 72% in E2 (2435.72 kg/ha) compared to the control. Therefore, based on the results of the studies, we can conclude that rhizobacteria and silicon can be integrated into the management of blast and upland rice productivity.