Transfer of leaf rust and stripe rust resistance genes Lr62 and Yr42 from Aegilops neglecta Req. Ex Bertol. to common wheat

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Continued genetic control of the cereal rusts depends on the availability of effective resistance genes. The wild relatives of wheat (Triticum aestivum L.) constitute a source of such genes. Wheat leaf rust (Puccinia triticina Eriks.) resistant Aegilops neglecta accession 155 was crossed with ‘Chinese Spring’. Resistant progeny were initially backcrossed to Chinese Spring and later to Chinese Spring-Short (a short-strawed near-isogenic line) to develop an addition line. Advanced backcross progeny segregated for a resistance gene (designated Lr62) located on an addition chromosome, as well as a resistant phenotype apparently contributed by dominant complementary genes of the wheat genomes. On its own, Lr62 produced infection type (IT); however, in the presence of the two complementary genes its expression was modified to an intermediate response. The addition chromosome appeared to have homeology with group 3 chromosomes of wheat. While attempting to transfer the resistance through allosyndetic pairing induction to a group 3 wheat chromosome, a spontaneous translocation occurred. Aneuploid and microsatellite analyses showed that the translocation involved wheat chromosome 6A, suggesting that the addition chromosome may also have partial homeology to group 6. Microsatellite and meiotic pairing data suggested the presence of a large segment of foreign chromatin replacing the entire 6AS arm and a proximal part of 6AL. Lr62 was effective against a wide range of South African and western Canadian Puccinia triticina pathotypes. In addition to Lr62, the translocation line, 03M119-71A, carried a seedling stripe rust resistance gene (designated Yr42) effective against South African pathotypes of P. striiformis. The resistance genes can be of significant commercial value, however, it may be necessary to further tailor this fairly big translocation through allosyndetic pairing induction.

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