GENE-FOR-GENE RELATIONSHIPS IN HOST: PARASITE SYSTEMS

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Abstract
Theoretical consideration of the origin of gene-for-gene relationships led to the conclusion that such relationships, postulated by Flor for the Linum:Melampsora system, should occur as a general rule in host:parasite systems. An ideal gene-for-gene system, with five related host and parasite loci, was designed to illustrate the properties inherent in gene-for-gene systems, and to illustrate a new method of analyzing for these properties. Analyses of published data of the Solanum:Phytopthora and Linum:Melampsora systems proved that gene-for-gene relationships are in fact operative in these systems and that Flor's hypothesis—that for each specific locus in the host determining resistance and susceptibility there is a specific and related locus in the parasite which determines virulence and avirulence—is correct. Analysis of Flor's data showed, however, that most of his "single-gene" differential varieties actually possess two or more genes for resistance, and that resistance genes in these varieties need not fall into allelic or closely linked groups.