Minerals affect plant health. They improve plant vigor indirectly by altering root exudates and changing the microflora population dynamics. The availability of potassium (K+) to the plant is highly variable due to the complex soil dynamics which is influenced by the root-soil interaction (Ashley et al., 2006). K+ is available to plants only in soluble form. Potassium can affect most of the biochemical and physiological function that influence plant’s susceptibility to disease. These processes include stomatal regulation, enzyme activation and solute transport which is in context to plant nutrition or disease control. Majority of bacterial and fungal diseases decreased with increasing K+ nutrition, whereas the viral diseases and nematode infection had inconsistent response to K+ nutrition (Ortel et al., 2024). K+ is involved in control of water and nutrient fluxes from roots to different plant organ tissues and organic molecules among distinct plant organ tissues, controlling cell osmosis, turgor and pH allowing adequate cell organelle status and movement (Sardans and Penuelas 2021). Shortage of K+ in plants induces many responses at different levels such as morphological, physiological, biochemical and molecular. Activation of signaling cascades including reactive oxygen species, phytohormones (ethylene, auxin and jasmonic acid), Ca2+ and phosphatidic acid is also triggered (Hafsi et al., 2014).
Potassium deficient plant tends to be more susceptible to infection (Wang et al., 2013). The K+ deficiency in plant is associated with lower cell-membrane resistance and higher concentrations of sugar and amino acids, which can increase the risk of pathogenic and herbivorous damage (Sardans and Penuelas 2021). In K+ deficient soil, cotton and other crops can be susceptible to Fusarium wilt and root rot caused by Fusarium oxysporum f. sp. (Zhang et al., 2016). The molecules that signal low K+ status in plant include reactive oxygen species and phytohormone such as auxin, ethylene and jasmonic acid (JA) (Ashley et al., 2006). Potassium deficiency may result in problem such as thinning of the cell walls, weakening of the trunk and branches, sugar accumulation in leaves and an increase in the amount of unused nitrogen. These effects may reduce plant resistance, thus facilitating entry and development of plant pathogens such as fungus and bacteria causing plant disease. The accumulation of sugar and amino acid in plant increases the risk of disease development (Bayindir and Kucukyumuk 2025). Potassium deficiency is associated with high synthesis and concentration of JA, activating defense mechanism and the activity of high-affinity selective K+ transporters in the cells of fine roots (Sardans and Penuelas 2021). Potassium deficient rice (Oryza sativa L.) is susceptible to diseases including stem rot (Maschmann et al. 2010), high potassium rate reduced brown spot in rice caused by Bipolaris oryzae (Carvalho et al., 2010). Davis et al.(2018) result suggest that induction of JA signaling pathway by low K+ status may protect barley plant against powdery mildew caused by Blumeria graminis but not against the fungal pathogen Rhynchosporium commune causing leaf scald disease. Potassium application creates a good micro-ecological environment for the root system by changing the K+ status, the root exudate and the rhizosphere microflora can reduce Verticillium wilt of cotton (Ju et al., 2020).
Potassium is required by plant to synthesize large biomolecules such as cellulose, starch and proteins. As a result, small molecule such as sugars, amino acids, organic acids and amides are reduced in the cell while there is an increase in concentration of phenols and these compound aid in plant resistance (Hasanuzzaman et al., 2018). Potassium when present in adequate concentration it can certainly increase the plant’s polyphenolic concentration, and which has a role in plant defense mechanisms (Tripathi et al., 2022). Adequate K+ increase phenol concentration and acts in providing plant resistance (Wang et al., 2013).
The variable effect of K+ on disease incidence could be affected on the amount of source of K+, plant and pathogen species and trial type (Wang et al., 2013). Strawberries when grown with increased potassium resulted in increased severity of anthracnose caused by Colletotrichum gloeosporioides whereas, minimum potassium application decreased anthracnose in strawberries (Nam et al., 2006). Potassium may also control plant disease. Bacterial stem rot caused by Erwinia carotovora subsp. carotoyora may be suppressed when high potassium-to-nitrogen ratio is supplied in nutrient solution of hydroponically grown tomato (Dhanvantari and Papasdopoulos 1994). Foliar application of potassium nitrate is effective in suppressing Alternaria leaf blight of cotton (Bhuiyan et al., 2007). High dose of K+ decreased incidence of Alternaria leaf blight of mustard (Khatun et al., 2011). Foliar application of potassium chloride can control fungal disease probably due to osmotic effects on the fungal pathogens, disrupting pathogen development and subsequent infection (Regmi and Shrestha 2018). Potassium deficiency generally reduces plant resistance due to decrease or eliminating environmental stress response proteins in cotton seedling xylem sap (Zhang et al., 2016). If pathogen evade the pre-formed defense system that is weakened in the root apoplast by potassium deficiency, then a more efficient defense mechanism is required. Active defense requires plant to recognize pathogens, signal and activate the related genes to fortify the cell wall with callose, lignin and hydroxyproline-rich glycoprotein, produce phytoalexins and induce pathogenesis-related proteins.
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