Dual Role of Bacillus velezensis EM-A8 in Maize: Biocontrol of Exserohilum Turcicum and Enhancement of Plant Growth

Northern corn leaf blight (NCLB), caused by <i>Exserohilum turcicum</i>, is a major foliar disease of maize worldwide. To develop sustainable alternatives that reduce chemical products, we evaluated <i>Bacillus velezensis</i> EM-A8 (GenBank accession number OL704805) as a biocontrol agent under greenhouse and field conditions. The aims of this study were as follows: (i) characterize phytohormone production in two formulations containing the BCA; (ii) assess the influence of the BCA on plant biomass and yield; (iii) compare the efficacy of both formulations in controlling NCLB under field conditions; and (iv) determine whether the treatments affected salicylic acid and phenolic compound levels in maize tissues. The strain 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 increased maize dry biomass by 30%. In field trials, both formulations effectively suppressed NCLB, reducing the number of symptomatic leaves by 25-50% compared with controls. Furthermore, treated plants exhibited yield increases exceeding 1000 kg/ha. These findings demonstrate that <i>B. velezensis</i> EM-A8 provides effective biocontrol of <i>E. turcicum</i> while simultaneously enhancing maize growth and yield under field conditions. Future work should aim to scale up the use of <i>B. velezensis</i> EM-A8 in integrated pest management programs and evaluate its long-term impact on soil microbiota, plant health, and yield sustainability.