Interactions Between Genes Controlling Pathogenicity in the Flax Rust Fungus

Abstract

Progeny obtained by self-fertilizing each of 2 strains of the flax [Linum usitatissimum] rust fungus (M. lini), and by intercrossing them, were individually tested for pathogenicity on 29 host-differential cultivars that possess 28 (or possibly 29) different resistance genes. The progeny segregated for pathogenicity on 19 of the differential cultivars. Pathogenicity on 14 of these cultivars was determined, in each case, by a single pair of allelic genes, with avirulence dominant to virulence. For each of the remaining 5 cultivars possessing resistance genes M1, L1, L7, L10 and LX, an avirulence/virulence gene pair (A/a) and an inhibitor gene pair (I/i) interact to determine pathogenicity, the only avirulent strains are those with genotypes iiAa and iiAA. The data are consistent with the assumption that a common inhibitor gene (or group of closely-linked inhibitor genes) is involved in determining pathogenicity on the L1, L7, L10 and Lx resistance genes and that this inhibitor gene (or genes) is closely linked to the inhibitor gene involved in determining pathogenicity on M1. The data also suggest that the avirulence genes AM1 and AM4 are linked (possibly very closely), that the differential cultivar Victory A possesses 2 genes conferring resistance (both of which belong to the M group [M1 and M4]) and that the differential cultivar Towner also possesses the M4 resistance gene in addition to the L8 gene.