Molecular Basis of Infection and Disease Resistance Defence

Plants face a multitude of attackers such as herbivorous insects and pathogenic microbes.
During the invasion process, plant pathogens degrade the cell wall by synthesizing and liberating cell wall-degrading enzymes.
Once pathogens penetrate the cell wall, the plant two-tiered innate immune system is activated to counter-attack pathogen invasion.
Whether the pathogen can infect a plant or not depends on:
the genes for pathogenicity and virulence present in the pathogen and
the genes for resistance or susceptibility present in the plant.
The estimated loss caused by pathogens is typically around 10 to 20%.
Plant disease resistance is generally divided into
Qualitative resistance (controlled by major R genes) and
quantitative resistance (conditioned by multiple genes)
R gene usually confers complete resistance to a specific pathogen or pathogen race.
Quantitative disease resistance (QDR) is controlled by multiple genes.
QDR leads to lower selection pressure against pathogen variants, thus tends to be more durable.
At the molecular level, defense systems often depend on:
the combination of a specific set of dominant R genes in the plant and
a corresponding set of dominant avirulence (Avr) genes in the pathogen
Expression of the Avr genes triggers plant defense responses governed by the product of the R gene.
This gene-for-gene resistance strategy underlies the molecular basis of defense systems in plants....

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