03/14/2026
When your soil and plants are "teaming with microbes" like Arbuscular Mycorrhizal Fungi for example. You now have an improved defense against pathogens. Check out this Article.
Plant Responses to Pathogenic Fungi in the Absence and Presence of Arbuscular Mycorrhizal Fungi
Plant Pathology MCQs: https://jeas.agropublishers.com/2025/12/plant-pathology-mcqs/
Seed Science MCQs: https://jeas.agropublishers.com/2025/12/seed-science-mcqs/
Plants continuously interact with both beneficial and pathogenic microorganisms in the rhizosphere. The attached figure contrasts plant defense dynamics under two scenarios: (A) absence of arbuscular mycorrhizal fungi (AMF) colonization and (B) presence of AMF colonization. The comparison highlights how AMF reshape host immunity, nutrient acquisition, and systemic resistance.
In the absence of AMF, plants rely solely on innate immune responses against invading pathogenic fungi. Two major pathogen lifestyles dominate:
Necrotrophs, which kill host cells and exploit dead tissue.
Biotrophs, which derive nutrients from living cells.
a) Necrotrophic Infection
Necrotrophic pathogens typically activate programmed cell death (PCD) pathways, facilitating tissue necrosis and disease progression. Resistance against necrotrophs is primarily mediated through the jasmonic acid (JA) and ethylene (ET) signaling pathways.
However, without symbiotic buffering, excessive PCD often increases susceptibility.
b) Biotrophic Infection
Biotrophs are generally countered by the salicylic acid (SA) pathway, which activates pathogenesis-related (PR) proteins and localized hypersensitive responses.
Yet antagonistic crosstalk between the SA and JA pathways can suppress balanced defense, thereby facilitating infection establishment.
c) Nutritional Constraints
Without AMF: Phosphorus (PO₄³⁻), zinc (Zn²⁺), potassium (K⁺), ammonium (NH₄⁺), and water uptake remain limited to the root depletion zone. Nutrient stress weakens immune competence, as defense responses are metabolically expensive. Thus, susceptibility arises from both physiological stress and suboptimal immune modulation.
2. Plant Response With AMF Colonization
AMF (phylum Glomeromycota) establish intracellular arbuscules in cortical cells, forming a bidirectional nutrient exchange interface (Smith & Read, 2008, Mycorrhizal Symbiosis).
a) Enhanced Nutrient and Water Uptake
AMF hyphal networks extend beyond the root depletion zone, significantly improving phosphorus acquisition and micronutrient uptake. Improved nutrition enhances host fitness and supports energy-demanding defense metabolism.
b) Priming and Defense Gene Activation
MAPK cascades
Pattern-triggered immunity (PTI)
Effector-triggered immunity (ETI)
AMF colonization primes host defense systems without constitutively activating them, a phenomenon termed mycorrhiza-induced resistance (MIR).
Primed plants exhibit faster and stronger activation of defense genes upon pathogen attack.
AMF influences hormonal crosstalk:
AMF influence hormonal crosstalk:
Enhanced JA/ET signaling improves resistance against necrotrophs.
Balanced SA responses improve control of biotrophs.
Reduced inappropriate PCD limits pathogen exploitation.
This hormonal recalibration increases resistance while minimizing fitness costs.
d) Induced Systemic Resistance (ISR)
AMF trigger systemic resistance comparable to rhizobacteria-mediated ISR. Defense metabolites accumulate in distal tissues, conferring whole-plant protection.
AMF function as belowground immune modulators, integrating nutrition and defense. Under field conditions, AMF colonization can reduce disease severity and improve crop resilience, particularly in low-input or stress-prone systems.
From an agroecological perspective, promoting AMF through reduced tillage, organic amendments, and minimized fungicide use may enhance sustainable disease management.
Photo credit: Elhamouly et al., 2022
DOI: 10.3389/fpls.2022.1044896
Plant Pathology MCQs: https://jeas.agropublishers.com/2025/12/plant-pathology-mcqs/
Seed Science MCQs: https://jeas.agropublishers.com/2025/12/seed-science-mcqs/
