Disease resistance refers to the ability of a plant to restrict, slow, or prevent the development of disease after exposure to a pathogen. There are several types of disease resistance in plants:
Horizontal resistance - provides resistance to all genetic variants (races or strains) of a pathogen but only to a limited extent. This type of resistance is generally governed by multiple genes and is less likely to be overcome by new pathogen races.
Vertical resistance - provides nearly complete resistance to some variants of a pathogen but almost no resistance at all to other variants. This type of resistance involves single R genes and is more easily overcome by pathogen mutation.
Complete resistance - the plant shows no disease symptoms after pathogen infection. This is generally governed by R genes.
Partial resistance - the plant shows reduced disease symptoms relative to a susceptible plant. This type of resistance slows but does not completely stop pathogen growth and reproduction.
Plants have innate immune systems that recognize general signals from many pathogens as well as specific signals from adapted pathogens. When a potential pathogen is detected, the plant initiates defense responses such as strengthening cell walls, producing antimicrobial compounds, and triggering localized cell death.
While all plants have general immune responses, some have additional R genes that recognize specific pathogen proteins and trigger stronger hypersensitive reactions. This resistance can be overcome when the pathogen mutates to avoid recognition.
Breeding for disease resistance involves identifying good source plants with R genes or partial field resistance and incorporating those resistance traits into elite crop lines through crosses. This allows crop varieties to be developed with strong specific resistance and good agronomic characteristics. Combining multiple types of resistance is key to durable disease control.
Some key practices for managing disease resistance include:
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