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Linkage Between Endopeptidase Ep-D1d and a Gene Conferring Leaf Rust Resistance (Lr19) in Wheat

Clark Atlanta Univ., Dep. of Biology, James P. Brawley Dr., Atlanta, GA 30314 and Sci. Res. Inst., 440 Westview Dr. S.W., Atlanta, GA 30310
Dep. of Agronomy, Georgia Station, Griffin GA 30223
USDA-ARS, Georgia Station, Griffin, GA 30223

^* Corresponding author.

Biochemical markers linked to pest resistance genes would be useful to plant breeders. This study was conducted to determine if biochemical markers could be found closely linked to genes conferring leaf rust resistance in wheat (Triticum aestivum L.). Near-isogenic lines have been developed in ‘Thatcher’ for a number of genes, Lrl to Lr31, conferring resistance to leaf rust, caused by Puccinia recondita Rob. ex Desm. Fifteen of these Thatcher near-isogenic lines were evaluated for the isozymendopeptidaseo Two of the near-isogenic lines (Lrl and Lrl9) had endopeptidase phenotypes that differed from the Thatcher backcross parent. The endopeptidase phenotype observed in the near isogenic line possessing Lrl9 was completely different from any other phenotype normally observed in wheat. The leaf rust resistant Thatcher near-isogenic line possessing Lrl9 was crossed with the leaf rust susceptible cultivar ‘GA 100’ (PI538257). The 59 F₂ progeny were grown in the greenhouse and evaluated for leaf rust resistance and endopeptidase phenotype. All F₂ progeny exhibiting the Lrl9 endopeptidase phenotype were resistant to leaf rust. Maximum likelihood estimation, using the F₂ phenotypic data, indicated a very tight linkage with a recombination value of 0.01 ± 0.009 map units for the Lrl9 and Ep-D1d loci. In addition, no recombinant F2 genotypes were found among the 30 F₂ plants for which F₃ progeny were obtained. Thus, the gene Lrl9, which confers resistance to leaf rust, and the gene Ep-Dld which encodes endopeptidase phenotype EP-Dld, are linked. This linkage will enable rapid detection of seedlings possessing Lrl9 in wheat improvement programs.

Received for publication August 17, 1992.