Disease resistance refers to the ability of a plant to prevent, tolerate, or overcome infection by a pathogenic organism such as a virus, bacteria, or fungus. There are two main types of disease resistance in plants:
- Passive resistance involves physical or chemical barriers that prevent the pathogen from successfully infecting the plant. Examples include waxy layers on leaves that block fungus entry, bark that resists insect attack, or antimicrobial compounds in plant tissues.
- Active resistance relies on the plant's immune system recognizing disease-causing microbes and mounting defense responses to stop infection. This can include signaling cascades that trigger local cell death to isolate the pathogen, production of reactive oxygen species or pathogenesis-related (PR) proteins with antimicrobial activity, and systemic acquired resistance (SAR) which protects the whole plant.
Some key points about disease resistance in plants:
- It is controlled by R genes which recognize molecular patterns associated with pathogens. Specific R genes provide resistance to specific pathogen strains.
- Resistant varieties are bred by plant breeders to introduce disease resistance traits from wild plant relatives into domesticated crop species.
- Using resistant varieties is a core principle of integrated pest management (IPM) programs which aim to first use genetic and biological control methods rather than chemical pesticides.
- There are tradeoffs to disease resistance. Strongly resistant varieties may invest more resources into defense which reduces yield potential. Weak resistance may succumb under high disease pressure. Breeders aim for durable, broad-spectrum resistance.
- Pathogens can evolve to overcome formerly resistant plant varieties. For example, new rust and blight races rendering wheat and potato varieties susceptible. This makes breeding for resistance an ongoing process.