Bacillus spp. are widely marketed and used in agricultural systems as antagonists to various phytopathogens, but it can also benefit the plant as plant growth promoters. Therefore, the longer presence of the bacterium in the rhizosphere would result in a prolonged growth-promoting benefit, but little is yet known about its persistence in the rhizosphere after seed coating. The objectives of this study were to evaluate the tomato growth promotion mediated by Bacillus licheniformis FMCH001 and Bacillus subtilis FMCH002 and the survival rate of these bacteria both in shoots and in the rhizosphere. The Bacillus strains used throughout this study were obtained from Quartzo® produced by Chr. Hansen. The application of a mixture of B. subtilis and B. licheniformis (Quartzo®) at concentrations 1 × 10⁸, 1 × 10⁹, and 1 × 10¹⁰ CFU mL⁻¹, as well as the application of B. subtilis and B. licheniformis individually at concentration 1 × 10⁸ CFU mL⁻¹, increased fresh and dry masses of shoot and root system, volume of root system, and length of roots of tomato plants when compared to control. Both Bacillus strains produced IAA after 48 h of in vitro. Bacillus colonies obtained from plant sap were morphologically similar to colonies of B. subtilis and B. licheniformis strains and were detected in inoculated on plants and not detected in control ones. A similar pattern was obtained through DNA-based detection (qPCR). Therefore, B. subtilis and B. licheniformis were able to produce auxin, promote tomato growth, and colonize and persist in the rhizosphere.

The rhizosphere is a narrow and dynamic region of plant root-soil interfaces, and it’s considered one of the most intricate and functionally active ecosystems on the Earth, which boosts plant health and alleviates the impact of biotic and abiotic stresses. Improving the key functions of the microbiome via engineering the rhizosphere microbiome is an emerging tool for improving plant growth, resilience, and soil-borne diseases. Recently, the advent of omics tools, gene-editing techniques, and sequencing technology has allowed us to unravel the entangled webs of plant-microbes interactions, enhancing plant fitness and tolerance to biotic and abiotic challenges. Plants secrete signaling compounds with low molecular weight into the rhizosphere, that engage various species to generate a massive deep complex array. The underlying principle governing the multitrophic interactions of the rhizosphere microbiome is yet unknown, however, some efforts have been made for disease management and agricultural sustainability. This review discussed the intra- and inter- microbe-microbe and microbe-animal interactions and their multifunctional roles in rhizosphere microbiome engineering for plant health and soil-borne disease management. Simultaneously, it investigates the significant impact of immunity utilizing PGPR and cover crop strategy in increasing rhizosphere microbiome functions for plant development and protection using omics techniques. The ecological engineering of rhizosphere plant interactions could be used as a potential alternative technology for plant growth improvement, sustainable disease control management, and increased production of economically significant crops

Rhizoctonia solani compromises the production of lima bean, an alternative and low-input food source in many tropical regions. Inoculation of bacterial strains has been used, but research on their biocontrol and growth promotion potential on lima bean is scarce. The objective of this study was to evaluate the effects of inoculation with rhizobacterial strains of the genera Bacillus, Brevibacillus, Paenibacillus, Burkholderia, Pseudomonas, and Rhizobium in combination or not with N₂-fixing Rhizobium tropici on the control of damping-off disease and growth promotion in lima bean plants. Greenhouse experiments were conducted to evaluate the inoculation with bacterial strains with biocontrol potential in combination or not with R. tropici in substrate infected with R. solani CML 1846. Growth promotion of these strains was also assessed. Strains of Brevibacillus (UFLA 02-286), Pseudomonas (UFLA 02-281 and UFLA 04-885), Rhizobium (UFLA 04-195), and Burkholderia (UFLA 04-227) co-inoculated with the strain CIAT 899 (Rhizobium tropici) were the most effective in controlling R. solani, reducing the disease incidence in 47–60% on lima bean. The promising strains used in the biocontrol assays were also responsive in promoting growth of lima bean under disease and sterile conditions. A positive synergistic effect of co-inoculation of different genera contributed to plant growth, and these outcomes are important first steps to improve lima bean production.

The integration of management methods for both diseases and weeds depends on the compatibility between the tools. Biological control represents an important strategy to cope with the integrated management of white mold (Sclerotinia sclerotiorum) through parasitism of sclerotia. However, its application in the field is more cost-effective if combined with the herbicide in a tank mix, as long as the products are compatible. Therefore, we aimed at (i) evaluating two compatibility test methodologies (constant exposure and different times) and (ii) two soybean crop seasons to infer the compatibility of Trichoderma-based products. In vitro bioassays were performed to assess the compatibility between herbicides (Haloxifope-p- methyl, Glyphosate N-ammonium salt, Fluasifope-p-butyl, Fomesafem, Chlorimuron ethyl and Imazapyc + Imazapyr) and two biocontrol agents (Trichoderma asperellum and Trichoderma harzianum). Thus, the recommended spray volume for each herbicide was added to the PDA culture medium (Potato-Dextrose-Agar) and then deposited in the center of the plate a disc of mycelium from each antagonist isolate (constant exposure). The tests with time of exposure were marked at times 0, 2, 4, 8 and 16 h (simulating tank mixing) and at the spp of each time were plated on PDA medium. For both tests, the mycelial growth and conidiogenesis of Trichoderma spp. were observed. The combination of herbicide and biocontrol was also tested in the field and sclerotia parasitism, white mold incidence and plant yield were assessed in two field trials. The constant exposure of the antagonists to herbicides revealed that no herbicide was compatible with the T. asperellum or T. harzianum. While in test, exposure time exhibited compatibility with either T. asperellum or T. harzianum, within a period of 2 to 8 h. Conclusively, the integration of biocontrol agents with the herbicide imazapique + imazapyr exhibited significant reductions in white mold disease incidence and conidia germination, along with effective parasitism of S. sclerotiorum and even the least compatible herbicide (glyphosate) resulted in significant reduction in the disease incidence and sustained yield when compared to the untreated control. Therefore, the integration of the biocontrol agent for white mold should always be considered, and the tank mixing of it with the herbicide represents a cost-effective alternative for the grower.

• Applying mixtures of microbial species/strains provides plant health benefits.
• Microbial compatibility is vital for consortium development.
• Consortia enhance microorganism performance to control plant disease.
• Field studies are needed to optimize the use of microbial consortia.
• In Brazil, multi-microbe biopesticides are becoming more common.

Abstract

Beneficial microbes play crucial role in modern agriculture, serving as biopesticides, biostimulants/biofertilizers, and alleviating abiotic stress in crops. Their multifaceted functions contribute significantly to crop health and sustainability, aligning with the principles of regenerative agriculture by minimizing carbon footprints and reducing dependence on agrichemical inputs. The concept of ‘microbial consortia’, involving the combination of multiple fungal and bacterial species or strains, has gained recognition for its potential advantages over single species/strains applications. This method aims to employ a spectrum of ecological functions, encouraging biological equilibrium within agricultural systems. Recent research highlights how microbial consortia can directly and indirectly enhance plant health, through various mechanisms and interactions with their host plants. This review presents examples demonstrating the efficacy of microbial consortia as biopesticides and biostimulants/biofertilizers. These consortia exhibit potential in managing plant diseases and pests, while also promoting plant growth and mitigating specific abiotic and biotic stresses in crops. This review examines real-world examples considering instances of success and failure, discusses methodologies employed for evaluating interactions, and also addresses challenges in the selection, production, and application of optimal microbial consortia for agricultural use providing valuable insights in the current and future prospects of microbial consortia in modern agriculture.