In a world with constant population growth, and in the context of climate change, the need to supply the demand of safe crops has stimulated an interest in ecological products that can increase agricultural productivity. This implies the use of beneficial organisms and natural products to improve crop performance and control pests and diseases, replacing chemical compounds that can affect the environment and human health. Microbial biological control agents (MBCAs) interact with pathogens directly or by inducing a physiological state of resistance in the plant. This involves several mechanisms, like interference with phytohormone pathways and priming defensive compounds. In Argentina, one of the world’s main maize exporters, yield is restricted by several limitations, including foliar diseases such as common rust and northern corn leaf blight (NCLB). Here, we discuss the impact of pathogen infection on important food crops and MBCA interactions with the plant’s immune system, and its biochemical indicators such as phytohormones, reactive oxygen species, phenolic compounds and lytic enzymes, focused mainly on the maize–NCLB pathosystem. MBCA could be integrated into disease management as a mechanism to improve the plant’s inducible defences against foliar diseases. However, there is still much to elucidate regarding plant responses when exposed to hemibiotrophic pathogens.

Northern corn leaf blight (NCLB), caused by Exserohilum turcicum, is a major foliar disease of maize worldwide. To develop sustainable alternatives that reduce chemical products, we evaluated Bacillus velezensis 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 B. velezensis EM-A8 provides effective biocontrol of E. turcicum while simultaneously enhancing maize growth and yield under field conditions. Future work should aim to scale up the use of B. velezensis EM-A8 in integrated pest management programs and evaluate its long-term impact on soil microbiota, plant health, and yield sustainability.

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.