LINKAGE BETWEEN ENDOPEPTIDASE EP-D1D AND A GENE CONFERRING LEAF RUST RESISTANCE (LR19) IN WHEAT

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 re sistance in wheat (Triticum aestivum L.). Near isogenic lines have bee n developed in 'Thatcher' for a number of genes, Lr1 to Lr31, conferri ng resistance to leaf rust, caused by Puccinia recondita Rob. ex Desm. Fifteen of these Thatcher near isogenic lines were evaluated for the isozyme endopeptidase. Two of the near isogenic lines (Lr1 and Lr19) h ad endopeptidase phenotypes that differed from the Thatcher backcross parent. The endopeptidase phenotype observed in the near isogenic line possessing Lr19 was completely different from any other phenotype nor mally observed in wheat. The leaf rust resistant Thatcher near-isogeni c line possessing Lr19 was crossed with the leaf rust susceptible cult ivar 'GA 100' (PI538257). The 59 F-2 progeny were grown in the greenho use and evaluated for leaf rust resistance and endopeptidase phenotype . All F-2 progeny exhibiting the Lr19 endopeptidase phenotype were res istant to leaf rust. Maximum likelihood estimation, using the F-2 phen otypic data, indicated a very tight linkage with a recombination value of 0.01+/-0.009 map units for the Lr19 and Ep-D1d loci. In addition, no recombinant F-2 genotypes were found among the 30 F-2 plants for wh ich F-2 progeny were obtained. Thus, the gene Lr19, which confers resi stance to leaf rust, and the gene Ep-D1d which encodes endopeptidase p henotype EP-D1d, are linked. This linkage will enable rapid detection of seedlings possessing Lr19 in wheat improvement programs.