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Genetics

Inheritance of Virulence of Melampsora lini Race 218. Glen D. Statler, Professor, Department of Plant Pathology, North Dakota State University, Fargo, ND 58102; Phytopathology 69:257-259. Accepted for publication 31 August 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-257.

A culture of race 218, Melampsora lini was selfed and the progeny were tested for virulence on flax lines each of which contained a pair of genes conditioning rust resistance. Race 218 was crossed with race 22, but only a limited number of F₁ cultures were derived. Race 218 and all of the S₁ cultures resulting from selfing race 218 were virulent on near-isogenic flax lines containing L⁵, L⁶, L⁷, L⁹, L¹¹, M¹, M², M⁴, and P¹ indicating that the genes for virulence were homozygous. Race 218 also was virulent on the line with L¹⁰. Segregation for virulence on the line with L¹⁰ may have been due to a temperature-sensitive factor. Race 218 and all the S₁ progenies tested were avirulent on lines containing L², N, P⁴, and Kugine indicating that race 218 is homozygous avirulent on lines with these resistance genes. Segregation ratios fit theoretical monogenic recessive ratios on isogenic lines possessing host genes K, L¹, L³, L⁴, L⁸, M, M³, M⁵, M⁶, N¹, P, P², and P³. Virulence on the line with N² probably was conditioned by a single recessive gene since there were only a few more cultures in the virulent category than would fit expected ratios. Two independently inherited recessive genes apparently conditioned virulence on the line with L. Chi-square tests indicated that virulence on several lines with alleles at the L locus and the P locus was linked. Usually virulence on most other lines with alleles at different loci was inherited independently; the few exceptions included virulence on lines with L⁸ and M which was apparently closely linked. These linkage patterns indicate that a deletion of a small segment carrying A_L 8 and A_M could cause virulence on flax lines carrying the corresponding resistance genes.