Crop Physiology and Protection
Crop Physiology and Protection
This domain covers photosynthetic pathways, water relations, growth regulators, photoperiodism, vernalization, pest and disease diagnosis, and integrated pest management.
Core rules
- C3 plants use the Calvin cycle and RuBisCO; C4 plants use PEP carboxylase and Kranz anatomy; CAM plants open stomata at night and fix carbon as organic acids.
- C4 plants generally have higher water-use efficiency and a lower CO₂ compensation point than C3 plants.
- Photoperiodism is the response to day length; vernalization is the cold treatment needed to induce flowering in some crops.
- Growth regulators include auxins, gibberellins, cytokinins, abscisic acid and ethylene.
- IPM combines cultural, mechanical, biological and chemical methods; the economic threshold level is the pest density at which control pays.
Worked example
Maize grows well at high temperature and light intensity and shows Kranz anatomy. Its first CO₂ fixation product is a four-carbon acid, so it is a C4 plant. The reasoning is based on anatomy plus the enzyme system, not simply on yield.
Mark-losing traps
- Mixing photoperiodism with vernalization.
- Treating ETL as zero pest population; ETL is an economic decision point.
- Calling every pesticide a fungicide; match the target organism to the chemical group.
- Assuming C4 plants also avoid photorespiration at night; CAM plants are the night-time CO₂ fixers.