Healthy plant has strong vigor and improved resistance to disease, and because of this there is less disease incidence. No single nutrient controls all diseases or favor disease control of any one group of plants (Huber and Graham 1999). Magnesium (Mg) is an essential mineral element and has both direct and indirect effect on disease. Mg is vital for photosynthesis, as it is a central atom in chlorophyll molecule (Sarraf et al., 2026). Magnesium ion (Mg2+) is key in fortifying plants against environmental stressors and diseases by reinforcing cell walls and spurring the synthesis of defense substances (Ahmed et al., 2023). Mg2+ has a role in capturing photon and the subsequent transfer of energy to the photosynthetic machinery of the plants (Ahmed et al., 2023; Igamberdiev and Kleczkowski 2011); Mg2+ also plays a significant role in transporting carbohydrate via phloem from leaves to sink organs such as root, shoot tips and seeds (Cakmak 2013; Jiao et al., 2023) and has a role in the maintenance of structural stability in plant cells. It aids in stabilizing cell structure such as cell membrane, ribosomes, mitochondria, chloroplasts and nucleic acid ensuring structural integrity and functional efficiency of plant cells (Ahmed et al., 2023). Mg functions as a cofactor for several enzymes involved in the synthesis of proteins, carbohydrates, lipids and nucleic acids, including ATPases, kinases, phosphatases, Rubisco and acetyl-CoA carboxylase (Chen et al., 2018; Sarraf et al., 2026). Depending on pathogen/ pest, plant species and environmental condition, Mg nutrition may increase or decrease disease incidence. Magnesium deficiency increases the severity of peanut leaf spot caused by Mycosphaerella arachidicola (Bledsoe et al., 1946; Huber and Jones 2012). Whereas high level of Mg increased susceptibility to bacterial leaf spot in pepper and tomato caused by Xanthomonas campestris pv. vesicatoria (Jones et al., 1983; Martin-Cardoso and Segundo 2025). High rates of Mg interfere with Ca uptake, which may increase incidence of disease such as bacterial spot of tomato and pepper or peanut pod rot (Huber and Jones 2013).
The high concentration of sugars in source leaves under Mg deficiency is due to impaired phloem transportation which may promote pathogen invasion and infection (Cakmak et al., 2013). The use of excessive amount of potash will cause very high content of K in plants but will lower Ca and Mg (Lucas and Scarseth 1947). High concentration of Ca or sodium in soil antagonize Mg absorption due to competition for binding sites on root plasma membranes, leading to Mg deficiency even in Mg-rich soils (Sarraf et al., 2026). A deficiency of Mg during growth reduces the structural integrity of the middle lamella and the production of energy necessary for defense function and inactivation of pathogen metabolites (Huber and Jones 2012). High level of sugars in tissue under Mg deficiency reduces the effectiveness of calcium in reducing post-harvest rot diseases of apple caused by Botrytis cinerea and Penicillium expansum (Huber and Jones 2012). A moderate increase in Mg supply induced a synergistic effect between K and Mg in the shoot of tomato plant, whereas high Mg supply severely inhibited K absorption due to an antagonistic effect (Qu et al., 2023).
Mg can complement or antagonize other minerals, which can result in different disease responses to Mg under different environmental conditions. Magnesium oxide is a promising agent for control of Fusarium wilt. (Fujikawa et al., 2021). Fusarium wiltpathogens tend to be less severe when adequate Mg is available; Mg also increases resistance of tissues to degradation by some pectolytic enzymes of macerating or soft rotting pathogens (Huber and Jones 2012). Addition of extra Mg to potting soil was associated with increased damping-off of Calendula (Elmer and Datnoff 2014). But when carnation was grown on calcareous soil, Mg application suppressed Fusarium wilt (Elmer and Datnoff 2014). The added Mg corrected the deficiency occurred due to high Ca concentration.
Mg suppresses brown spot disease severity in rice caused by Bipolaris oryzae and preserves photosynthetic performance by allowing better stomatal conductance and consequently, greater availability of CO2 at the carboxylation sites (Moreira et al., 2015). The severity of take-all of wheat caused by Gaeumannomyces graminis var. tritici increasedwith increasing pH but not with increasing amount of Ca and Mg (Reis et al., 1983). Maize plant infected with Spiroplasma kunkelii display symptomslike plant growing in Mg-deficient soil. Spiroplasma alters plant Mg absorption (Nome et al., 2009).
Magnesium oxide nanoparticle (MgO NP) induces systemic resistance in tomato plant against Ralstonia solanacearum causing bacterial wilt (Imada et al., 2015). Rapid generation of reactive oxygen species (ROS) such as super oxide in tomato roots may be due to the reaction between MgO NP and polyphenols present in the roots. ROS not only limits pathogen ingress but also play a role in activating local and systemic defense response inducing pathogenesis related (PR) protein genes (Henry et al., 2013). Caution should be exercised in Mg application as nutrient. A reasonable application of Mg can increase crop yield and enhance plant resistance to diseases.
References:
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BIOLOGICAL PROCESSES- A NATURE'S GIFT 