1996 Volume 62 Issue 2 Pages 95-100
Using the simulation model for a four gene system on host-pathogen relationship, we studied the principles included in determination of types (cross- and noncross-types) of nonrandom associations between avirulence loci in a pathogen population. Analyses were carried out by giving some changes in host genotype frequencies which bring equilibrium conditions in frequencies of pathogen genotypes. Determination of types [cross-type (C) and noncross-type (N)] of nonrandom association was conducted by complicated but definite principles. When four avirulence genes (a, b, c and d) and four corresponding virulence ones (+a, +b, +c and +d) and 16 genotypes consisting of four avirulence loci were considered, definite characteristics on determination of types of nonrandom associations appeared depending on the number of susceptibility genes [S0, S1, S2, S3 and S4 (subscript is the number of susceptibility genes)]. When, for example, a part of a host genotype S0 (ABCD) was replaced by another host genotype S2 (for example, AB++), that is, (S0→S2), nonrandom association patterns, NCCCCC, CNCCCC, CCCNCC, CCNCCC, CCCCNC and CCCCCN, were observed for host genotypes AB++, A+C+, +BC+, A++D, +B+D and ++CD belonging to S2, respectively. NCCCCC is a nonrandom association type for interactions between avirulence loci, a-b, a-c, a-d, b-c, b-d, and c-d, respectively. For determination of the patterns, there were two cases; in some cases a new host genotype (genotype after the replacement; called receptor, for convenience, in the simulations) gave influence, and in other cases, it was the old host genotype (genotype before replacement; donor in the simulations). In the former cases, combinations of a resistance gene and a susceptibility gene induced a cross-type nonrandom association, and combinations between a resistance gene and another resistance gene and between a susceptibility gene and another susceptibility gene induced noncross-type nonrandom association. In contrast, when a host genotype (S2) was changed to S0, the pattern became to be reversed, that is, CNNNNN, NCNNNN, NNNCNN, NNCNNN, NNNNCN and NNNNNC, respectively, in the above example.
