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Inheritance of Virulence of a Mutant Isolate of Melampsora lini. Glen D. Statler, Professor, Department of Plant Pathology, North Dakota State University, Fargo 58105-5012; Phytopathology 84:761-764. Accepted for publication 29 April 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-761.

The inheritance of virulence was studied in a cross between two isolates of Melampsora lini with widely different virulence patterns. The F1 of the cross (X82) was subjected to mutagenesis with nitrosoguanidine (MNNG). One mutant, isolate 33-27, had mutations to virulence on lines with host genes L8 and N2, and a mutation to avirulence on the line with M2 and was chosen to study the inheritance of virulence for a mutant isolate of M. lini. Although S1 progenies from isolate 33-27 fit the same segregation ratios previous to MNNG treatment on many near-isogenic lines, differences in segregation occurred at several loci after MNNG treatment. These changes included lines on which X82 was homozygous avirulent and 33-27 S1 progenies segregated 3:1, lines on which X82 progeny segregated 15:1 and 3:1 in the 33-27 S1 progenies, and lines on which S1 progenies from X82 segregated 3:1 and 13:3 in S1 progenies from 33-27. S1 progenies of isolate 33-27 segregated approximately 9:7, the same as the parental culture on lines with L8 and N2, even though this isolate was virulent to these loci after MNNG treatment. Isolate 33-27 had a mutation to avirulence at AM2. Progenies from selfing isolate X82 segregated approximately 3:1 on the line with M2, whereas S1 progenies of isolate 33-27 segregated approximately 7:9. Segregation of S1 progenies from X82 on several near-isogenic lines fit 3:1 ratios; however, 13:3 or 7:9 segregation ratios in progenies of 33-27 after treatment may suggest that expression of an additional recessive gene is affected by MNNG treatment.