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Allelic and Linkage Relations among Genes for Stem Rust Resistance from Triticum turgidum, ‘Mindum,’ ‘Acme’ Selection, ‘Palestine,’ and ‘Khapli’¹

The objective was to determine allelic and linkage relations among genes for resistance to stem rust (Puccinia graminis Pers. f. sp. tritici Eriks. & E. Henn) in 13 lines of tetraploid wheat (Triticum turgidum L.) derived from crosses of susceptible ‘Marruecos 9623’ with resistant ‘Mindum’ (three lines), ‘Acme’ selection (three lines), ‘Khapli’ emmer (four lines), and ‘Palestine’ (three lines). Each of the 13 lines had a single gene for resistance to stem rust. A partial diallel cross was made among the lines, and F₂ seedlings were tested for reaction to cultures 111-SS2 and 56-1 of stem rust. Absence of segregation indicated that the parents had allelic or closely linked genes for resistance; segregation for resistance and susceptibility indicated nonallelism.

A uniformly resistant F₂ from a cross between lines Srda-2 (gene for resistance from Acme selection) and Srdm-1 (gene for resistance from Mindum) indicated that these lines had allelic (or closely linked) genes for resistance. Also, lines Srda-3, Srdm-2, and Plt-C (genes for resistance from Acme selection, Mindum, and Palestine, respectively) had allelic (or closely linked) genes for resistance. All other crosses segregated resistant and susceptible seedlings which indicated that the parental lines had different single genes for resistance.

Twenty-eight crosses appeared to segregate into three classes, one like the parent having the highest level of resistance, one like the parent having the lowest level of resistance, and one susceptible. Of the 28 crosses, segregation in 19 was a good fit to a 12:3:1 ratio. Genes conditioning high levels of resistance usually masked those conditioning low levels.

Segregants more resistant than either parent occurred in 11 crosses and indicated that genes for resistance from the two parents had cumulative effects. Genes for resistance in parental lines in each of five crosses conditioned similar levels of resistance, and most of these F₂s segregated in ratios of approximately 15 resistant:1 susceptible. Statistically significant deviations from tested ratios occurred in the F₂ from 16 crosses, but the direction of the deviations did not imply linkage. The F₂ data of seven crosses were not tested by chi-square because sample sizes were small or segregation ratios were irregular.

Key Words: Durum wheat • Puccinia graminis f. sp. tritici • Host plant resistance • Disease • Inheritance • Epistasis • Cumulative effects • Duplicate dominant genes

² Research geneticist and research plant pathologist, USDA-ARS, Dep. of Agronomy and Dep. of Plant Pathology, respectively, North Dakota State Univ., Fargo.

Received for publication January 11, 1982.

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