Gene-for-Gene Relationships in Host: Parasite Systems

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.

Studies of genes controlling specific host-parasite interactions in flax and its rust

“…Testcross refers to the procedure of crossing F1 progeny of these chosen parents with a variety homozygous for the recessive alleles of Mx and M, namely, Hoshangabad (see table 1), used in these studies as the so-called "universal susceptible" (Person, 1959). Assuming genes M' and M can recombine with a frequency p and maintain their specific action after recombination, the expected frequencies of the four testcross progeny phenotypes are set out in table 2.…”

“…Person (1959) suggested that, within the range of rust strains by which Abyssinian and Leona are classified by Flor (1956) to possess one gene each, 2 and P3 respectively, there are, in fact, two and three such genes respectively. However, Lawrence (1977) produced clear evidence inconsistent with such a hypothesis.…”

Virulence heterozygosity and gametic phase disequilibria in two populations of Puccinia recondita (wheat leaf rust fungus)

“…Host-parasite interactions in cereal rust diseases are governed by a complementary genetic relationship that has been referred to as a gene-for-gene relationship (Person, 1959;Flor, 1971). Although there are differing interpretations of this phenomenon (Person, 1959;Person & Mayo, 1974;Keen, 1982;Ellingboe, 1984), the essential element of a gene-for-gene system is that specific genes in the host and parasite interact to condition a compatible or incompatible relationship.…”

“…Although there are differing interpretations of this phenomenon (Person, 1959;Person & Mayo, 1974;Keen, 1982;Ellingboe, 1984), the essential element of a gene-for-gene system is that specific genes in the host and parasite interact to condition a compatible or incompatible relationship. A consequence of genetic specificity is that a host resistance gene is effective only when the corresponding virulence is not prevalent in the rust population.…”

“…In an ideal gene-for-gene system, the rust isolate must have the necessary virulence allele(s) at a specific locus in order to be virulent on a host line with one specific resistance gene. Although two-for-one relationships have been described (Dyck & Samborski, 1974), the total pattern of compatible and incompatible interactions in these cases is the same as in a one-to-one relationship (Person, 1959).…”