The gene-for-gene relationship was discovered by Harold Henry Flor[1][2][3][4] who was working with rust (Melampsora lini) of flax (Linum usitatissimum). Flor was the first scientist to study the genetics of both the host and parasite and to integrate them into one genetic system.[5] Gene-for-gene relationships are a widespread and very important aspect of plant disease resistance.