Nitrogen fixation in cereals requires microbial symbiosis beyond plant genetics

Steps:

• Selective breeding improves heritable traits within a species by choosing parent plants with desired characteristics.
• Cereal crops like wheat and rice naturally lack nitrogen-fixing abilities, relying on soil fertilizers.
• Nitrogen fixation occurs via symbiotic bacteria in legumes, not cereals, so breeding can't introduce this trait.
• Other traits like yield or stress resistance vary genetically in cereals and can be enhanced through selection.

Why A is correct:

• Nitrogen fixation depends on specific symbiotic relationships with Rhizobium bacteria, which cereals cannot develop through breeding alone, as defined by plant-microbe interaction biology.

Why the others are wrong:

• B: Drought resistance arises from genetic variations in water-use efficiency, selectable in breeding programs.
• C: Low-temperature tolerance involves heritable cold-hardiness genes, improved by selecting resilient varieties.
• D: Seed number is a polygenic trait directly influenced by plant genetics, enhanced via yield breeding.

Final answer: A