Wheat faces frequent challenges such as foliar diseases and abiotic stresses, including water deficits, extreme temperatures, and nutrient deficiencies, which negatively impact its development and final grain yield. Strategic foliar nutrition is a tool that significantly contributes to strengthening wheat during the vegetative phase, improving its disease resistance and metabolism under stress.
Micronutrients such as manganese (Mn), copper (Cu), and zinc (Zn) play a crucial role in activating defense enzymes and vitamins and antioxidant compounds, making plants less susceptible to foliar pathogens. Foliar nutrition acts as a reinforcement for soil fertilization, as well as correcting deficiencies with more immediate action, delivering nutrients directly to the leaves, which promotes faster and more effective assimilation. This technique is especially effective for immediately filling nutritional deficiencies that were not met through soil application, in addition to meeting the plant's needs at crucial stages of its development, such as when it needs to strengthen its defense mechanisms.
The role of micronutrients in plant defense
Manganese (Mn) - The activator of systemic resistance. Manganese strengthens wheat resistance by activating enzymes that produce antifungal compounds (lignins, phenolics, and flavonoids). It helps reduce fungal incidence through enzyme activation and the formation of structural barriers, hindering the penetration of pathogens. These combined mechanisms are essential for plant defense and sustainable disease management in the crop.
Furthermore, manganese plays a structural strengthening role through the synthesis of lignin and phenolic compounds. This creates an effective physical barrier against pathogen penetration and significantly reduces water loss through transpiration. Furthermore, manganese participates in the photosynthetic process, ensuring continuous energy production even under unfavorable climatic conditions.
Copper (Cu) - The cell wall reinforcer. Copper is an essential micronutrient that acts as a key component of enzymes involved in lignin synthesis, strengthening cell walls against pathogens. A deficiency compromises lignification, increasing vulnerability to diseases such as powdery mildew, leaf rust, septoria leaf spot, and stem bacterial diseases. As a metabolic regulator, it protects cell membranes through lipid stabilization and improves photosynthetic efficiency under stress.
Furthermore, copper reduces the efficiency of ROS (reactive oxygen species), preventing oxidative damage and maintaining productive performance. Its multifunctional action combines structural reinforcement, metabolic protection, and pathogen control, resulting in more resilient plants with better development, even under adverse conditions.
Zinc (Zn) - The antioxidant regulator. Zinc (Zn) deficiency compromises antioxidant defense by reducing the activity of the SOD (superoxide dismutase) enzyme, leading to the accumulation of O?? radicals. These radicals attack membrane lipids, causing peroxidation and loss of cellular integrity. Zn is also essential for stabilizing bonds between proteins and sulfhydryl (-SH) groups, maintaining the structure of defense enzymes. Without sufficient Zn, these proteins become unstable, impairing resistance mechanisms. The result is a plant that is more vulnerable to pathogens and less able to respond positively to stress.
Studies confirm the importance of applying manganese (Mn), copper (Cu), and zinc (Zn)
Several scientific studies demonstrate the importance of applying micronutrients such as manganese (Mn), copper (Cu), and zinc (Zn) to plants. These elements are essential for plant development, participating in fundamental physiological processes such as photosynthesis, enzyme synthesis, cellular respiration, and resistance to biotic and abiotic stresses.
Moreira et al. (2020) demonstrated that zinc (Zn) reduces the severity of wheat blast (Magnaporthe oryzae) by modulating hydrogen peroxide production and cell death. Efficacy varied depending on the cultivar and the applied Zn concentration. Cakmak (2000) highlights that zinc (Zn) plays a crucial role in protecting plant cells against oxidative stress by activating the enzyme superoxide dismutase (SOD), which neutralizes reactive oxygen species (ROS). During the vegetative stage of wheat, this action is vital, as environmental and biotic stress can compromise cellular integrity and growth. An adequate supply of Zn, therefore, strengthens the plant's antioxidant defense and contributes to its physiological health.
Studies conducted by Stepien and Wojtkowiak (2016) show that foliar application of copper (Cu), manganese (Mn), and zinc (Zn) to wheat crops during the vegetative stage had positive effects on grain quality, with impacts on protein content, gluten, and sedimentation index. These elements also influence physiological parameters essential to the plant's resistance to environmental stresses, indirectly contributing to its defense.
According to Broadley et al. (2012), the micronutrients Cu, Mn, and Zn are essential for plant metabolism. During the vegetative stage, these nutrients are crucial for the structural and functional development of the plant, and their deficiency can compromise not only growth but also natural defense mechanisms against pathogens.
Final Considerations
Foliar application of micronutrients acts as part of an integrated management system, reinforcing physiological barriers and reducing dependence on chemical interventions, but without replacing them. More than just supplying nutrients, foliar nutrition strengthens the plant's natural defense mechanisms, reducing the pressure for chemical interventions and contributing to production systems.
This integrated nutritional management approach is a valuable tool for sustainable, high-yield production systems. Therefore, foliar application of micronutrients to wheat crops should not only be viewed from a nutritional perspective, but also as a strategy to protect the plant against stress and strengthen its defense mechanisms against diseases.
Text written by Omega Saul and Gabrielly dos Passos Morigi, students in the Agronomy program at UFSM, Frederico Westphalen campus, members of the Tutorial Education Program - PET Agricultural Sciences, under the supervision of their tutor, Professor Dr. Claudir José Basso.
BIBLIOGRAPHIC REFERENCES:
BROADLEY, Martin et al. Function of Nutrients: Micronutrients. 2012. Available at: https://www.sciencedirect.com/science/article/abs/pii/B9780123849052000078?via%3Dihub. Accessed on: June 5, 2025.
CAKMAK, Ismail. Possible roles of zinc in protecting plant cells from damage by reactive oxygen species. 2000. Available at: https://nph.onlinelibrary.wiley.com/doi/epdf/10.1046/j.1469-8137.2000.00630.x. Accessed on: June 5, 2025.
COSTA, Magna Maria Macedo Nunes. Micronutrients in Agriculture. Campina Grande: Embrapa Algodão, 2024. 44 p. eu. color. (Documents/Embrapa Algodão, e-ISSN 2966-0343; 297). Available at: https://www.infoteca.cnptia.embrapa.br/infoteca/bitstream/doc/1164119/1/MICRONUTRIENTES-AGRICULTURA.pdf. Accessed: June 5, 2025.
MACIEL, João Leodato Nunes et al. Healthy nutrition: the relationship between the balanced supply of mineral nutrients to wheat plants and the occurrence of biotic diseases in the crop. Cultivar Magazine, v. 264, p. 32–36, 2021. Available at: https://www.infoteca.cnptia.embrapa.br/infoteca/bitstream/doc/1132492/1/Trigo-nutricao-saudavel.pdf. Accessed on: June 5, 2025. Moreira, C.; Camacho, M.A. & Graichen, F.A.S. (2020). Reducing wheat blast severity with foliar application of zinc sulfate. Summa Phytopathologica, 46, 3, 255-259.
STEPIEN, Arkadiusz; WOJTKOWIAK, Katarzyna. Effect of foliar application of Cu, Zn, and Mn on yield and quality indicators of winter wheat grain. 2015. Available at: https://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-58392016000200012. Accessed on: June 5, 2025.
Photo: Marlon Bastiani/PDI 3tentos
