We formulate a spatially realistic population-genetic model for ascertaining the synergetic effect between genetic and spatial composition of the host population on the pathogen spread reinforced by evolutionary processes. We show that spatial arrangement of host genotypes is crucial to the efficacy of host genetic diversification. In particular, the reductive effect of multigenic resistance on the pathogen density can be produced by a random patterning of monogenic resistances. Random patterns can reduce both density and genetic diversity of the pathogen population and delay invasion promoted by sexual recombination. By contrast, patchy distributions diversify pathogen population and, hence, reduce the efficacy of resistance genes. The proposed approach provides theoretical support for studying fast emergence and spread of novel pathogen genotypes carrying multiple virulence genes. It has a practical applicability to design innovative strategies for the most appropriate deployment of plant resistance genes.