Disease resistance refers to the ability of a plant to prevent, limit, or overcome infection when exposed to a pathogen such as a virus, bacteria, or fungus. There are several types of disease resistance in plants:
- Passive resistance involves physical or chemical barriers that prevent pathogens from successfully infecting the plant. Examples include waxy layers on leaves, bark on stems, or antimicrobial compounds on the plant surface.
- Active resistance relies on the plant's immune system recognizing molecules from specific pathogens and mounting defense responses to stop infection. This can include signaling cascades that trigger hypersensitive cell death to isolate the infected area or production of antimicrobial proteins and chemicals.
- There are two main forms of active genetic resistance in plants:
- Race-specific resistance involves a gene-for-gene interaction between the products of an avirulence (Avr) gene in the pathogen and a matching resistance (R) gene in the plant. This leads to a strong defense response like programmed cell death in the infected area.
- Quantitative/polygenic resistance is conferred by multiple genes each contributing partial resistance. This leads to slower developing and less severe infections by pathogens as compared to susceptible plant varieties.
Breeding for disease resistance is an important goal for many crop breeding programs and for management of agricultural diseases. Identifying new sources of resistance genes from wild relatives and selectively breeding these traits into cultivated varieties
helps sustain crop health and productivity. Combining multiple genetic resistance factors also leads to more durable resistance that is less likely to be overcome by pathogen evolution over time.
Some key challenges with relying solely on host resistance include:
- Pathogens can evolve to defeat single gene resistance, especially when large areas are planted to varieties with the same resistance gene
- Tradeoffs may exist between disease resistance and other important agricultural traits like yield potential and quality
- Constant breeding efforts are needed to introgress new resistance traits into desirable crop backgrounds
Therefore, an
integrated approach combining genetic host resistance, cultural practices, biological controls, and judicious use of pesticides is required for effective and sustainable disease management in agriculture.