Genetic linkage maps based on restriction fragment length polymorphisms are useful for many purposes; however, different populations are required to fulfill different objectives. Clones from the linkage map(s) are subsequently probed onto populations developed for special purposes such as gene tagging. Therefore, clones contained on the initial map(s) must be polymorphic on a wide range of genotypes to have maximum utility. The objectives of this research were to (i) calculate polymorphism information content values of 51 low-copy DNA clones and (ii) use the resulting values to choose potential mapping parents. Polymorphism information content was calculated using gene diversity by classifying restriction fragment patterns on a diverse set of 18 wheat genotypes. Combinations of potential parents were then compared by examining both the proportion of polymorphic clones and the likelihood that those mapped clones would give a polymorphism when used on other populations. Genotype pairs were identified that would map more highly informative DNA clones compared with a population derived from the most polymorphic potential parents. The methodologies used to characterize clones and rank potential parents should be applicable to other species and types of markers as well.

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. × T. touschii (Coss.) Schmal.] × 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.

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