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Comparative Virulence of Basidiospore and Urediospore Cultures of Three Pathogenic Races of Melampsora lini. G. D. Statler, Professor, Department of Plant Pathology, North Dakota State University, Fargo 58105; R. E. Gold, graduate assistant, Department of Plant Pathology, North Dakota State University, Fargo 58105. Phytopathology 70:555-557. Accepted for publication 15 November 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-555.

The virulence of monokaryotic basidiospore cultures was compared to that of dikaryotic urediospore cultures in three races of Melampsora lini on 29 isogenic lines of flax (Linum usitatissimum), each with a single gene for resistance. The three races previously had been selfed to determine heterozygosity on the 29 isogenic lines. In most cases, basidiospores were virulent only on host isogenic lines for which they carried the gene for virulence. Exceptions to this general observation included comparisons of race 1 on lines with L8, M2, M4, N, and P4; race 370 on lines L, L1, M2, N1, and P4; and race 218 on P4. Exceptions to the observation that basidiospores infect only host cultivars for which they carried the gene for virulence were of three types: (i) those with urediospore cultures homozygous avirulent and basidiospore cultures virulent on that host line; (ii) those with homozygous virulent urediospore cultures and basidiospores that produced only a few poorly developed pycnia; and (iii) those with urediospore cultures heterozygous for virulence but with avirulent basidiospore cultures. Cultures with urediospore cultures avirulent and basidiospores virulent on an isogenic line (case i) were selfed on that isogenic line; the resulting cultures resembled parental urediospore cultures which were avirulent on that isogenic line on which basidiospores were virulent.

Additional keywords: flax rust, fungal genetics, pycnial reaction, urediospore virulence.