GENETICS OF PATHOGENICITY IN THREE RACES OF LEAF RUST ON FOUR WHEAT VARIETIES

Abstract

Populations of self-fertilized cultures of races 9, 11 and 161, "backcross" selfed progeny of race 11, F₁ cultures of races 9 × 11 and 11 × 161, and F₂ cultures of races 9 × 161 were used to study the genetics of virulence on the wheat varieties Democrat, Sinvalocho, Bage and Klein Aniversario and backcross lines developed from them.Race 9 was homozygous avirulent on all the host varieties tested. Selfed populations of race 11 segregated for a recessive gene, p3, for virulence on Democrat × Thatcher⁶ (Lr3), Sinvalocho and Sinvalocho × Thatcher². Race 11 has an additional dominant gene for virulence on the latter two varieties. Race 11 appears to have p3 plus a second gene(s) for virulence or a modifier(s) of the dominant allele of p3 for virulence on Sinvalocho × Prelude⁶ (Lr3). This would correspond to a modifier or suppressor in the genetics of resistance of Sinvalocho × Prelude⁶. Race 11 was homozygous for avirulence on Bage, heterozygous for p3 and one other gene for virulence on Bage × Thatcher⁸. This race was heterozygous for two genes for virulence on Klein Aniversario and for one gene on backcross lines derived from this variety. These genes were independent of p3. The data of the "backcross" selfed progeny of race 11 agreed in general with the above. Race 161 was segregating for a dominant gene for virulence on Democrat, Democrat × Thatcher⁶ and Sinvalocho × Prelude⁶, and for a recessive gene on Bage and Klein Aniversario × Thatcher⁶. It was homozygous avirulent on Klein Aniversario and homozygous virulent on Bage × Thatcher⁸. The pathogenicity of the F₁ cultures of races 11 × 161 suggested that the two races have virulence genes at the same locus. These data and those from the F₂ populations of races 9 × 161 supported the results from the selfed populations.