Molecular mapping and validation of the microsatellite markers linked to the Secale cereale-derived leaf rust resistance gene Lr45 in wheat

The mode of inheritance of wheat leaf rust resistance gene Lr45 was studied at seedling stage under greenhouse conditions against leaf rust race 77-5 in two F₂populations derived from the crosses between Thatcher (Tc)+Lr45 and two susceptible cultivars Agra Local and NI5439. The genetic analysis in F₂:₃progeny validated the F₂results which unambiguously showed segregation for a single dominant gene. Genetic analysis in F₂and BC₁F₁generations against five other leaf rust races confirmed the single dominant gene inheritance of Lr45. Mapping was carried out with 92 microsatellite markers specific to chromosome 2A on the F₂population of the cross Agra Local × Tc+Lr45. Out of seven markers linked to the gene, four (gwm372, gwm275, gpw3167 and gwm122) were co-dominant and the other three (cfd168, cfd6 and gwm249) showed dominance, amplifying the allele only in the susceptible parent. The genetic map of 13.1 cM was constructed based on the results in 140 homozygous resistant and homozygous susceptible plants. cfd168 was the closest marker linked to Lr45, followed by gwm372. These markers were validated on the NI5439 × Tc+Lr45 F₂population, 12 different backcross lines carrying Lr45 and near-isogenic lines, mostly in Tc background isogenic for 46 different Lr genes belonging to both native and alien species. The marker gwm122 was found to be monomorphic. The closest co-dominant marker gwm372 showed reduced polymorphism. Two sequence-based primer pairs, G372 ₉₄ and G372 ₁₈₅ , were designed and validated. Hence, the markers G372 ₉₄ and G372 ₁₈₅ closely linked to the gene can serve as robust co-dominant markers for utilization of Lr45 in wheat improvement.