Genes for Resistance to Flax Rust in the Flax Cultivars Towner and Victory A and the Genetics of Pathogenicity in Flax Rust to theL8Gene for Resistance

Abstract

The flax (Linum usiatissimum) cultivars Towner and Victory A possess the L8 and M4 genes for resistance to flax rust (Melampsora lini), respectively. A previous hypothesis was that Towner also has M4. Putative L8 and M4 lines were derived from Towner by breeding, and these were tested with 18 different strains of flax rust, together with 29 differential cultivars. The putative M4 line reacted as expected, but the putative L8 line gave the same reactions as Bison, which carries L9. This suggested that the laboratory stock of Towner had L9 and M4 rather than L8 and M4. This was confirmed by testing two other cultivars. Bisbee and B13 .times. Towner, which were expected to posses L8, with the same 18 strains of flax rust. These gave the same reactions, with one exception, and different reactions to Towner or the putative L8 line. The exception was caused by P1, which was present in Bisbee in addition to L8 but absent from B13 .times. Towner. These results suggest that the cultivar used as Towner by some previous workers was not Towner, but an unknown cultivar carrying L9 and M4. Consequently, the true stock of Towner may be assumed to possess only L8. Progeny from three families of flax rust, previously tested only on the unknown cultivar used as Towner, were tested on B13 .times. Towner, which carries L8. These tests revealed that pathogenicity to L8 was controlled by an avirulence gene pair. I-L8/.alpha.-L8, and an inhibitor gene pair, I-L8 is linked to previously described inhibitor genes affecting the A-L1, A-L7, A-L10, and A-M1 avirulence genes.