Mapping genes conferring and suppressing leaf rust resistance in wheat

Leaf rust, caused by Puccinia recondita Roberge ex Desmaz. f. sp. tritici Eriks. & E. Henn., is a serious disease of wheat (Triticum aestivum L.) worldwide. We evaluated leaf rust resistance in a RFLP-mapping population of wheat inbred lines developed from a synthetic [T. turgidum L. x T. tauschii (Coss.) Schmal.] x T. aestivum cross, using inoculation trials performed on seedlings and adult plants. Map locations were assigned for seedling resistance genes Lr10 (chromosome arm 1AS), Lr23 (2BS), Lr27 (3BS), and Lr31 (4BL), and the adult-plant resistance gene Lr34 (7DS). The previously reported interaction between Lr27 and Lr31, requiring the presence of both genes for resistance to avirulent rust pathotypes, was confirmed. Lr23, effective in the durum parent ('Altar 84') of the synthetic, was suppressed in the synthetic and in one fourth of the inbred lines by a T. tauschii gene on homoeologous chromosome arm 2DS. This suppressor, designated as SuLr23, appears to be specific for Lr23 and may be orthologous to the gene. DNA markers are useful in refining the characterization of resistance genes and their interactions, toward the goal of constructing durably resistant cultivars via marker-controlled accumulation of specific genes.