Dual Role of <em>Bacillus velezensis</em> EM-A8 in Maize: Biocontrol of <em>Exserohilum turcicum</em> and Enhancement of Plant Growth

Northern corn leaf blight (NCLB), caused by the hemibiotrophic fungus Exserohilum turcicum, is a major foliar disease of maize worldwide. Reducing dependence on chemical fungicides requires the development of sustainable strategies to manage foliar diseases in economically important crops. As an eco-friendly alternative, we evaluated a biocontrol agent previously isolated in our laboratory (Bacillus velezensis EM-A8; GenBank accession number OL704805) and investigated its effects on maize under both greenhouse and field conditions. The aims of this study were: (i) characterize phytohormone production in two different formulations containing the biocontrol agent; (ii) assess the influence of the bacterium on plant biomass and yield; (iii) compare the efficacy of the two formulations in controlling NCLB under field conditions; and (iv) determine whether the formulations affected salicylic acid and phenolic compound levels in maize tissues. Our results showed that B. velezensis EM-A8 synthesized a broad spectrum of phytohormones, including salicylic acid, indoleacetic acid, indolebutyric acid, jasmonic acid, abscisic acid and gibberellic acid, as well as cytokinins such as kinetin, zeatin, and 6-benzylaminopurine. Foliar application of the bacterium increased maize dry biomass by 30%. In field trials, both formulations effectively suppressed NCLB, reducing the number of symptomatic leaves by 25–50% relative to untreated controls. Furthermore, treated plants exhibited yield increases exceeding 1,000 kg/ha. In conclusion, formulations containing B. velezensis EM-A8 provided effective biocontrol of E. turcicum while simultaneously enhancing maize grain yield under field conditions.