Biocontrole de Fusarium verticillioides e promoção de crescimento de milho por bactérias isoladas de milho e sorgo

Abstract

In recent years, changes in cropping systems to improve agricultural production have favored an increase in the occurrence and severity of diseases and the intensive use of fungicides to control phytopathogens. However, the indiscriminate use of fungicides can negatively affect the environment and increase pathogen resistance. Furthermore, in some cases, such as Fusarium verticillioides, there are no effective chemical fungicides to control the fungus. Fusarium verticillioides is considered one of the primary pathogens of maize. This pathogen can cause seed losses, seedling death, stem rot, root and ear rot, and damages to stored grains. In addition, F. verticillioides produces fumonisins and mycotoxins harmful to humans and animals, which are obstacles to international trade. The difficulty of fungal control has stimulated research involving integrated disease management, with biological control being a feasible strategy with the potential for advantageous and sustainable use. Furthermore, some fungi-antagonistic bacteria may also perform functions like plant growth promoters. Thus, these organisms are ideal candidates for developing bioproducts. In this study, three bacteria isolated from maize and two isolated from sorghum were evaluated as candidates for biological control of maize pathogenic fungi and plant growth promoters. Preliminary tests in vitro showed the antagonistic activity of these bacteria against important pathogenic fungi of maize crops. Genomic sequencing revealed that the bacterial strains belong to the Bacillus velezensis species (LIS05, IM14, and CT02), Paenibacillus ottowii (LIS04), and Pseudomonas aeruginosa (IPR45). Analysis of bacterial filtrates by UPLC-MS and genomic analysis revealed that different antifungal metabolites inhibited the growth of Fusarium verticillioides, namely, iturin, fengycin, and surfactin (B. velezensis), quinolone and rhamnolipid (P. aeruginosa) and polymyxin (P. ottowii). Furthermore, the five isolates' genome analysis revealed other genes involved in synthesizing bioactive metabolites. The potential of these strains as biocontrol agents and plant growth promoters was validated by greenhouse and field experiments. Under controlled conditions, using isolates, individually or in combination with other bacteria or chemical fungicides, the treatments favored the improvement of seed germination, plant height, stalk diameter, plant dry matter, and root dry matter. In field evaluations, all isolates, individually or in combination, were efficient in reducing the stalk rot caused by F. verticillioides. The treatments using two bacteria or bacteria plus fungicides efficiently prevented yield losses by plants inoculated with F. verticillioides. Furthermore, these selected bacteria showed in vitro characteristics for plant growth promotion, which were confirmed by greenhouse tests. The combination of two B. velezensis isolates (CT02 + IM14) promoted increases of 18.1% in plant height, 15.1% in stem diameter, 44% in shoot dry mass MSPA, 72, 4% in the dry mass of MSR roots, and 46.8% in the total dry mass. This work presents results concerning how the selected microorganisms control phytopathogens and the proportion of the plant-protective effect of the antagonistic bacteria in controlling F. verticillioides. In addition, the results open new perspectives for using these bacteria to develop multifunctional biofungicides.