Several genes at different loci control resistance in the host. Several genes at different loci control pathogenicity in the pathogen. Genes for host resistance are dominant. Genes for a virulence are dominant in the rust. Genotypes and phenotypes of resistant flax cultivars and two races of flax rust.
Subscript numerals identify the locus.
Flor concluded that during their coevolution, the host and the pathogen developed complementary genetic systems. Note that that dominance is generally associated with the production of a functional gene product. Alleles that fail to make a functional product are recessive. The goal of the breeder in the race-specific resistance game is to produce cultivars that will recognize certain features of the pathogen so that the defense reaction will be triggered upon penetration. The countermove of the pathogen is to lose the genetic capacity to produce the recognized feature and thus be able to enter the host unrecognized and establish infection.