Plants have evolved both general and highly-specialized defense mechanisms that function to prevent diseases caused by the majority of microbial pathogens they encounter. Highly-specialized defense is governed by specific interactions between pathogen avr (avirulence) genes' loci and alleles of the corresponding plant disease resistance (R) loci. These defences can be very dynamic as microbes from the same species can act differently in their co-evolution with the specific host plant, which in turn has similarly evolved its response to external threats.

There have been major...