Gene for Gene hypothesis was 1^st observed in

Gene for Gene hypothesis was 1^st observed in Linseed rust.
The gene-for-gene relationship was discovered by Harold Henry Flor who was working with rust (Melampsora lini) of flax (Linum usitatissimum).
The inheritance of both resistance in the host and parasite's ability to cause disease is controlled by pairs of matching genes. One is a plant gene called the resistance (R) gene. Gene-for-gene relationships are a widespread and very important aspect of plant disease resistance.