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New Genes for Rust Resistance in Flax. D. E. Zimmer, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Fargo, North Dakota 58102; V. E. Comstock, Research Agronomist, Agricultural Research Service, U.S. Department of Agriculture, Fargo, St. Paul Minnesota 55101. Phytopathology 63:777-780. Accepted for publication 7 January 1973. DOI: 10.1094/Phyto-63-777.

Two (and possibly three) genes in flax, Linum usitatissimum, were identified which condition resistance to all races of the rust pathogen, Melampsora lini (Ehrenb.) Lev., including the virulent South American races. Progenies from individual plant selections from accessions C.I. 1888, C.I. 1911, and C.I. 2008 were resistant to races of rust that collectively attack the 26 known genes for resistance. Segregation ratios obtained in the F2 and testcrosses indicated that resistance of each selection was monogenic and dominant. F2 segregations were observed from crosses between three new accessions and five monogenic tester lines, each having dominant alleles for one of the five known rust-conditioning loci. The resistance of C.I. 1888 and C.I. 1911 was found to be conditioned by a gene at the P locus and that of C.I. 2008 by a gene at the M locus. These genes were designated P4 and M6.

Additional keywords: disease resistance, breeding, multiple alleles.