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Interactions Between Genes Controlling Pathogenicity in the Flax Rust Fungus. G. J. Lawrence, Graduate student, Department of Genetics, University of Adelaide, South Australia 5000, Present address: Department of Agronomy, Waite Agricultural Research Institute, Glen Osmond, South Australia 5064; G. M. E. Mayo(2), and K. W. Shepherd(3). (2)Senior lecturer, Department of Genetics, University of Adelaide, South Australia 5000; (3)Senior lecturer, Department of Agronomy, Waite Agricultural Research Institute, Glen Osmond, South Australia 5064. Phytopathology 71:12-19. Accepted for publication 17 July 1979. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-12.

Progeny obtained by self-fertilizing each of two strains of the flax rust fungus (Melampsora 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. It was concluded that 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 five cultivars possessing resistance genes M1, L1, L7, L10, and Lx, it was concluded that an avirulence / virulence gene pair (A/α) and an inhibitor gene pair (I/i) interact to determine pathogenicity and that the only avirulent strains are those with genotypes ii Aα and ii AA. 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 two 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.

Additional keywords: gene-for-gene relationship.