Inheritance of leaf rust resistance in the CIMMYT wheat Weebill 1

The CIMMYT spring wheat Weebill 1 has near-immune levels of adult plant resistance (APR) to leaf rust caused by Puccinia triticina Eriks. To determine the genetic basis of resistance in seedlings and adult plants Weebill 1 was crossed with two susceptible parents Jupateco 73S and 'Thatcher'. Advanced F_4:5, F_4:6, and F_5:7 recombinant inbred lines (RIL) populations from Jupateco 73S/Weebill 1 and BC₁F₂ populations from Thatcher/Weebill 1 were derived. The F_5:7 RILs and BC₁F₂ families were tested as seedlings with five races of P. triticina. The F₁ and F_4:5, F_4:6, and F_5:7 RILs of Jupateco 73S/Weebill 1 were evaluated in plots in Mexico and St. Paul. The Jupateco 73S/Weebill 1 RILs and Thatcher*2/Weebill 1 F₂ families segregated for Lr14b, an unknown seedling leaf rust resistance gene derived from Weebill 1 in both crosses, and Lr17a derived from Jupateco 73S in the RIL population. Lr17a was mapped to the distal end of chromosome 2AS and was linked to microsatellite maker Xgwm636 at a distance of 4.0 cM. The seedling genes did not condition effective resistance in the field plots with races used in the field trials. The segregation ratio in the RILs and F₂ families indicated the presence of three to four APR genes in Weebill 1. One of the APR genes was linked to the seedling gene Lr14b on chromosome 7BL and reduced leaf rust by 47% in St. Paul and 31% in Mexico. Based on the haplotypes of DNA markers, we do not believe that any of the APR genes is Lr34.