The development of codominant PCR/RFLP based markers for the flax rust-resistance alleles at the L locus

The flax L locus exists as a single gene with at least 13 alleles with diff erent rust-resistance specificities. With regards to resistance to North Am erican races of flax rust the L-2, L-6, and L-11 alleles are of major impor tance. Molecular markers have been developed by screening primer sets, whos e sequences were based on the nucleotide sequence of L-6, for their ability to amplify segments of the L gene. One primer combination was found to amp lify only the L-6 or L-11 alleles and another primer set was found to ampli fy the 3' end of all important L alleles. The latter primer set yielded a 1 .3 kb fragment which upon digestion with the endonuclease MboI generated RF LP patterns unique to L-2, L-6, L-9, and L-11. The application of PCR marke rs to a set of 22 cultivars, comprised of deregistered, recent, and yet to be released cultivars verifies genetic studies done by previous workers and demonstrates the usefulness of the markers for following segregation of L alleles in crosses amongst wide or narrow selections of cultivars. Overall, the results confirmed that L-6 is present in many Canadian flax cultivars. However, in several recently-released flax cultivars that have rust resist ance conditioned by genes at other loci, the L-9 allele was detected. These molecular markers will be useful in marker-assisted selection and the intr oduction of new genes for rust resistance in the flax breeding programs.