IDENTIFICATION OF MOLECULAR MARKERS LINKED TO THE AGROPYRON ELONGATUM-DERIVED LEAF RUST RESISTANCE GENE LR24 IN WHEAT

The objective of this study was to identify molecular markers linked t o the wheat leaf rust resistance gene Lr24 derived from Agropyron elon gatum (3DL/3 Ag translocation). Two near isogenic lines (NILs), 'Arina ' and Lr24/7 ''Arina'', were screened for polymorphism at the DNA lev el with 115 RFLP probes. Twenty-one of these probes map to the homoeol ogous group 3. In addition, 360 RAPD primers were tested on the NILs. Six RFLP probes showed polymorphism between the NILs, and 11 RAPD prim ers detected one additional band in the resistant NIL. The genetic lin kage of the polymorphic markers with Lr24 was tested on a segregating F-2 population (150 plants) derived from a cross between the leaf rust resistant Lv24/7 ''Arina'' and the susceptible spelt (Triticum spelt a) variety 'Oberkulmer'. All 6 RFLP markers were completely linked to Lr24: one was inherited as a codominant marker (PSR1205), one was in c oupling phase (PSR1203) and 4 were in repulsion phase (PSR388, PSR904, PSR931, PSR1067) with Lr24. The localization of these probes on chrom osome 3D was confirmed by nulli-tetrasomic analysis. Distorted,genotyp ic segregation was found for the codominant RFLP marker PSR1205. This distortion can be explained by the occurrence of hemizygous plants. On e of the 11 RAPD markers (OPJ-09) also showed complete linkage to the Lr24 resistance gene. The polymorphic RAPD fragment was cloned and seq uenced. Specific primers were synthesized, and they produced an amplif ication product only in the resistant plants. This specific marker all ows a reliable and rapid screening of a large number of genotypes in p ractical breeding. Analysis of 6 additional lines containing Lr24 reve aled that 3 lines have a smaller chromosomal segment of A. elongatum t han lines derived from 'Agent', a commonly used gene donor for the Lr2 4 resistance gene.