How do pests and pathogens reduce yields?

Climate change is expected to intensify both biotic (pests and diseases) and abiotic (temperature, drought, salinity, etc.) risks to crop production by altering environmental conditions that affect plant physiology, pest dynamics, and soil stability.

Effects on Abiotic Risks

1. Temperature Extremes
   • Rising global temperatures cause heat stress, damaging enzymes, reducing pollen viability, and shortening grain-filling periods in crops like rice and wheat.
   • More frequent cold snaps in variable climates lead to frost injury in subtropical crops such as sugarcane and banana.
2. Drought and Flooding
   • Irregular rainfall patterns increase drought frequency, leading to water scarcity and soil desiccation in arid regions.
   • Conversely, heavy rainfall events and flooding result in oxygen-deficient soils, impairing root respiration and nutrient uptake.
   • The combined occurrence of drought and salinity stress has become common in coastal and semi-arid zones.
3. Salinity and Soil Degradation
   • Rising sea levels and increased irrigation from saline water sources intensify soil salinization, particularly in delta and coastal regions.
   • Salinity reduces root water absorption, disrupts ion homeostasis, and causes nutrient imbalance in sensitive crops like maize and beans.
4. Atmospheric Changes
   • Elevated CO₂ levels can initially enhance photosynthesis, but long-term effects include nutrient dilution (lower protein and micronutrient content).
   • Higher ozone (O₃) concentrations damage chloroplasts and oxidative balance, leading to premature leaf senescence.

Effects on Biotic Risks

1. Increased Pest Pressure
   • Warmer climates allow insect pests like aphids and caterpillars to survive milder winters, expand their geographic range, and complete more generations per year.
   • Longer growing seasons promote pest population explosions, especially in tropical and subtropical zones.
2. Pathogen Evolution and Spread
   • Higher temperatures and humidity favor fungal pathogens (e.g., rusts and blights) and enhance viral transmission through insect vectors.
   • Pathogen virulence and mutation rates increase under fluctuating weather, leading to more aggressive strains.
3. Cross-Interaction between Biotic and Abiotic Stress
   • Climate-induced drought or heat stress weakens plant defenses, making crops more susceptible to pathogens and herbivory.
   • Combined stresses alter hormone signaling (e.g., abscisic acid and salicylic acid balance), disrupting plants’ ability to respond effectively to both threats.