What is Disease Resistance?
Disease resistance refers to the ability of a plant to restrict, slow, or ward off disease when exposed to a pathogen. It is an important trait that plant breeders select for to help reduce crop losses from diseases.
There are two main types of disease resistance in plants:
- Vertical resistance - Also called qualitative or race-specific resistance. This type of resistance is controlled by a single gene and is effective against specific races of a pathogen. It typically leads to a strong defense response. But vertical resistance can be overcome by new races of the pathogen, making it less durable.
- Horizontal resistance - Also called quantitative or race-non-specific resistance. This type of resistance is controlled by multiple genes and provides resistance against all races of a pathogen. Horizontal resistance triggers a weaker defense response than vertical resistance. But it is more durable over time.
Plants have various complex physical and biochemical mechanisms to defend themselves from disease-causing pathogens like fungi, bacteria, viruses, and nematodes. These disease resistance mechanisms may include:
- Structural barriers like thick cell walls, cuticles, bark that physically block pathogens
- Chemical barriers like antimicrobial compounds and proteins that inhibit or kill pathogens
- Hypersensitive response that quickly kills plant cells around an infection to stop further spread
- Systemic acquired resistance that protects the whole plant against a broad range of pathogens
Breeding crops for increased horizontal disease resistance aims to introgress multiple minor genes into elite cultivars to quantitatively improve their overall level of resistance. This can be done via several breeding methods such as:
- Hybridization between resistant and susceptible lines
- Backcross breeding to transfer resistance genes
- Genomic selection to accumulate many small-effect genes
- Genetic engineering to insert resistance genes
Improving crop disease resistance through breeding is crucial for developing high-yielding and sustainable agricultural systems. It reduces reliance on chemical pesticides and fungicides, decreases crop losses and waste, and increases food security. Continual breeding efforts are needed to keep up with the evolution of plant pathogens in the field.