Genetic interaction of adult plants and pathogens of wheat leaf rust: gen-na-gen or gen-on-the genes

In experiments with pathotype Puccinia triticina, a virulent to leaf rust resistance genes Lr 9, 19 and 24, there is evidence that that the pathogen to overcome resistance gene occurs in steps: first appear leaf rust pathogen genotypes, overcoming resistance of seedlings and then layering of different leaves of adult plants.